diff --git a/src/Event.cc b/src/Event.cc
index be7cd2c..e650809 100644
--- a/src/Event.cc
+++ b/src/Event.cc
@@ -1,1485 +1,1496 @@
 /**
  *  \authors   The HEJ collaboration (see AUTHORS for details)
  *  \date      2019-2023
  *  \copyright GPLv2 or later
  */
 #include "HEJ/Event.hh"
 
 #include <algorithm>
 #include <boost/rational.hpp>
 #include <cassert>
 #include <cstdlib>
 #include <iomanip>
 #include <iterator>
 #include <memory>
 #include <numeric>
 #include <optional>
 #include <ostream>
 #include <sstream>
 #include <string>
 #include <utility>
 
 #include "HEJ/event_types.hh"
 #include "fastjet/ClusterSequence.hh"
 #include "fastjet/JetDefinition.hh"
 #include "fastjet/PseudoJet.hh"
 
 #include "LHEF/LHEF.h"
 
 #include "HEJ/Constants.hh"
 #include "HEJ/EWConstants.hh"
 #include "HEJ/PDG_codes.hh"
 #include "HEJ/RNG.hh"
 #include "HEJ/exceptions.hh"
 #include "HEJ/LorentzVector.hh"
 #include "HEJ/utility.hh"
 
 namespace HEJ {
 
     /**
      * returns all EventTypes implemented in HEJ
      */
     size_t implemented_types(std::vector<Particle> const & bosons){
       using namespace event_type;
       // no bosons
       if(bosons.empty()) return FKL | UNO | QQBAR;
       // 1 boson
       if(bosons.size()== 1) {
       switch (bosons[0].type) {
         case ParticleID::Wp:
         case ParticleID::Wm:
+        case ParticleID::Z:
         case ParticleID::Z_photon_mix:
           return FKL | UNO | QQBAR;
         case ParticleID::h:
           return FKL | UNO;
         default:
           return non_resummable;
         }
       }
       // 2 bosons
       if(bosons.size() == 2) {
         // Resum only samesign W events
         if(bosons[0].type == ParticleID::Wp && bosons[1].type == ParticleID::Wp) {
           return FKL;
         }
         else if(bosons[0].type == ParticleID::Wm && bosons[1].type == ParticleID::Wm) {
           return FKL;
         }
       }
 
       return non_resummable;
     }
 
   namespace {
     using std::size_t;
 
     //! LHE status codes
     namespace lhe_status {
       enum Status: int {
         in = -1,
         decay = 2,
         out = 1,
       };
     }
     using LHE_Status = lhe_status::Status;
 
     //! true if leptonic W decay
     bool valid_W_decay( int const w_charge,
                         std::vector<Particle> const & decays
     ){
       assert(std::abs(w_charge) == 1);
       if(decays.size() != 2) // no 1->2 decay
         return false;
       const int pidsum = decays[0].type + decays[1].type;
       if( std::abs(pidsum) != 1 || pidsum != w_charge ) // correct charge
         return false;
       // leptonic decay (only check first, second follows from pidsum)
       if( w_charge == 1 ) // W+
         return is_charged_antilepton(decays[0]) || is_neutrino(decays[0]);
       // W-
       return is_charged_lepton(decays[0]) || is_antineutrino(decays[0]);
     }
 
-    //! true for Z decay to charged leptons
+    //! true for Z decay to leptons
     bool valid_Z_decay(std::vector<Particle> const & decays){
       if(decays.size() != 2) // no 1->2 decay
         return false;
       if(decays[0].type != anti(decays[1].type)) {
         return false;
       }
       // leptonic decay (only check first, second follows from above)
       return is_anylepton(decays[0]);
     }
 
+    bool valid_Z_decay_to_neutrinos(std::vector<Particle> const & decays){
+      return (decays.size() == 2)
+        && (decays[0].type == anti(decays[1].type))
+        && is_anyneutrino(decays[0]);
+    }
+
     //! true if supported decay
     bool valid_decay(std::vector<Particle> const & decays){
       return valid_W_decay(+1, decays) ||       // Wp
              valid_W_decay(-1, decays) ||       // Wm
              valid_Z_decay(    decays)          // Z/gamma
       ;
     }
 
     /// @name helper functions to determine event type
     //@{
 
     /**
      * \brief function which determines if type change is consistent with Wp emission.
      * @param in                      incoming Particle id
      * @param out                     outgoing Particle id
      * @param is_qqbar                Current both incoming/both outgoing?
      *
      * \see is_Wm_Change
      */
     bool is_Wp_Change(ParticleID in, ParticleID out, bool is_qqbar){
       using namespace pid;
       if(!is_qqbar && (in==d_bar || in==u || in==s_bar || in==c))
         return out ==  (in-1);
       if( is_qqbar && (in==d || in==u_bar || in==s || in==c_bar))
         return out == -(in+1);
       return false;
     }
 
     /**
      * \brief function which determines if type change is consistent with Wm emission.
      * @param in                      incoming Particle id
      * @param out                     outgoing Particle id
      * @param is_qqbar                Current both incoming/both outgoing?
      *
      * Ensures that change type of quark line is possible by a flavour changing
      * Wm emission. Allows checking of is_qqbar currents also.
      */
     bool is_Wm_Change(ParticleID in, ParticleID out, bool is_qqbar){
       using namespace pid;
       if(!is_qqbar && (in==d || in==u_bar || in==s || in==c_bar))
         return out ==  (in+1);
       if( is_qqbar && (in==d_bar || in==u || in==s_bar || in==c))
         return out == -(in-1);
       return false;
     }
 
     /**
      * \brief checks if particle type remains same from incoming to outgoing
      * @param in                      incoming Particle
      * @param out                     outgoing Particle
      * @param is_qqbar                Current both incoming/outgoing?
      */
     bool no_flavour_change(ParticleID in, ParticleID out, bool is_qqbar){
       const int qqbarCurrent = is_qqbar?-1:1;
       if(std::abs(in)<=pid::top || in==pid::gluon)
         return (in==out*qqbarCurrent);
       return false;
     }
 
     bool is_gluon_to_Higgs(const ParticleID in, const ParticleID out) {
       return in == pid::gluon && out == pid::Higgs;
     }
 
     /**
      * \brief check if we have a valid Impact factor
      * @param in                      incoming Particle
      * @param out                     outgoing Particle
      * @param is_qqbar                Current both incoming/outgoing?
      * @param W_change                returns +1 if Wp, -1 if Wm, else 0
      */
     bool is_valid_impact_factor(
       ParticleID in, ParticleID out, bool is_qqbar, int & W_change
     ){
       if( no_flavour_change(in, out, is_qqbar) || is_gluon_to_Higgs(in, out)) {
         return true;
       }
       if( is_Wp_Change(in, out, is_qqbar) ) {
         W_change+=1;
         return true;
       }
       if( is_Wm_Change(in, out, is_qqbar) ) {
         W_change-=1;
         return true;
       }
       return false;
     }
 
     bool is_extremal_higgs_off_quark(
       const ParticleID in,
       const ParticleID extremal_out,
       const ParticleID out
     ) {
       return in == out && extremal_out == pid::higgs && is_anyquark(in);
     }
 
     //! Returns all possible classifications from the impact factors
     // the beginning points are changed s.t. after the the classification they
     // point to the beginning of the (potential) FKL chain
     // sets W_change: + if Wp change
     //                0 if no change
     //                - if Wm change
     // This function can be used with forward & backwards iterators
     template<class OutIterator>
     size_t possible_impact_factors(
       ParticleID incoming_id,                                   // incoming
       OutIterator   & begin_out, OutIterator   const & end_out, // outgoing
       int & W_change, std::vector<Particle> const & boson,
       bool const backward                                       // backward?
     ){
       using namespace event_type;
 
 
       if(begin_out == end_out) return non_resummable;
       // keep track of all states that we don't test
       size_t not_tested = qqbar_mid;
       if(backward)
         not_tested |= unof | qqbar_exf;
       else
         not_tested |= unob | qqbar_exb;
 
       // Is this LL current?
       if( is_valid_impact_factor(incoming_id, begin_out->type, false, W_change) ){
         ++begin_out;
         return not_tested | FKL;
       }
       // q -> H q and qbar -> H qbar are technically not LL,
       // but we treat them as such anyway
       const auto next = std::next(begin_out);
       if(
         // first ensure that the next particle is not part of the *other* impact factor
         next != end_out
         && is_extremal_higgs_off_quark(incoming_id, begin_out->type, next->type)
       ) {
         std::advance(begin_out, 2);
         return not_tested | FKL;
       }
 
       // or NLL current?
       // -> needs two partons in two different jets
       if( std::distance(begin_out, end_out)>=2
       ){
         auto next = std::next(begin_out);
         // Is this unordered emisson?
         if( incoming_id!=pid::gluon && begin_out->type==pid::gluon ){
           if( is_valid_impact_factor(
                 incoming_id, next->type, false, W_change )
           ){
             // veto Higgs inside uno
             assert(next!=end_out);
             if( !boson.empty() && boson.front().type == ParticleID::h
             ){
               if(  (backward && boson.front().rapidity() < next->rapidity())
                 ||(!backward && boson.front().rapidity() > next->rapidity()))
               return non_resummable;
             }
             begin_out = std::next(next);
             return not_tested | (backward?unob:unof);
           }
         }
         // Is this QQbar?
         else if( incoming_id==pid::gluon ){
           if( is_valid_impact_factor(
                 begin_out->type, next->type, true, W_change )
           ){
             // veto Higgs inside qqbar
             assert(next!=end_out);
             if( !boson.empty() && boson.front().type == ParticleID::h
             ){
               if(  (backward && boson.front().rapidity() < next->rapidity())
                 ||(!backward && boson.front().rapidity() > next->rapidity()))
               return non_resummable;
             }
             begin_out = std::next(next);
             return not_tested | (backward?qqbar_exb:qqbar_exf);
           }
         }
       }
       return non_resummable;
     }
 
     //! Returns all possible classifications from central emissions
     // the beginning points are changed s.t. after the the classification they
     // point to the end of the emission chain
     // sets W_change: + if Wp change
     //               0 if no change
     //               - if Wm change
     template<class OutIterator>
     size_t possible_central(
       OutIterator & begin_out, OutIterator const & end_out,
       int & W_change, std::vector<Particle> const & boson
     ){
       using namespace event_type;
       // if we already passed the central chain,
       // then it is not a valid all-order state
       if(std::distance(begin_out, end_out) < 0) return non_resummable;
       // keep track of all states that we don't test
       size_t possible = UNO | EXTREMAL_QQBAR;
 
       // Find the first quark or antiquark emission
       begin_out = std::find_if(
         begin_out, end_out,
         [](Particle const & p) { return is_anyquark(p); }
       );
       // end of chain -> FKL
       if( begin_out==end_out ){
         return possible | FKL;
       }
 
       // is this a qqbar-pair?
       // needs two partons in two separate jets
       auto next = std::next(begin_out);
       if(
         next != end_out
         && is_valid_impact_factor(begin_out->type, next->type, true, W_change)
       ){
         // veto Higgs inside qqbar
         if( !boson.empty() && boson.front().type == ParticleID::h
             && boson.front().rapidity() > begin_out->rapidity()
             && boson.front().rapidity() < next->rapidity()
         ){
           return non_resummable;
         }
         begin_out = std::next(next);
         // remaining chain should be pure FKL (gluon or higgs)
         if(std::any_of(
              begin_out, end_out,
              [](Particle const & p) { return is_anyquark(p); }
            )) {
           return non_resummable;
         }
         return possible | qqbar_mid;
       }
       return non_resummable;
     }
 
     namespace {
       bool is_parton_or_higgs(Particle const & p) {
         return is_parton(p) || p.type == pid::higgs;
       }
 
       bool decay_conserves_charge(
         Particle const &parent,
         std::vector<Particle> const &products
       ) {
         auto charge_diff = charge(parent);
         for (auto const &p : products) {
           charge_diff -= charge(p);
         }
         return charge_diff == 0;
       }
 
       bool charge_conserved(Event const &ev) {
         boost::rational<int> charge_diff{0};
         for (auto const &in : ev.incoming()) {
           charge_diff += charge(in);
         }
         for (auto const &out : ev.outgoing()) {
           charge_diff -= charge(out);
         }
         if (charge_diff != 0) return false;
 
         return std::all_of(
           ev.decays().begin(), ev.decays().end(),
           [&ev](auto const &decay) {
             auto const &[parent, products] = decay;
             return decay_conserves_charge(ev.outgoing()[parent], products);
           });
       }
 
       bool decay_conserves_momentum(
         Particle const &parent,
         std::vector<Particle> const &products,
         const double tolerance
       ) {
         fastjet::PseudoJet total_p;
         for (auto const &p : products) total_p += p.p;
         return nearby_ep(parent.p, total_p, tolerance);
       }
 
       bool event_momentum_conserved(Event const &ev, const double tolerance) {
         return momentum_conserved(ev, tolerance)
           && std::all_of(
             ev.decays().begin(), ev.decays().end(),
             [&ev, tolerance](auto const &decay) {
               auto const &[parent, products] = decay;
               return decay_conserves_momentum(
                 ev.outgoing()[parent], products, tolerance);
             });
       }
 
       template <class Container>
       bool massless_particles_onshell(
         Container const &c,
         const double tolerance
       ) {
         return std::all_of(
           c.begin(), c.end(),
           [tolerance](Particle const & p) {
             return is_massive(p) || p.m() < tolerance * std::max(p.E(), 1.0);
           }
         );
       }
 
       bool all_massless_particles_onshell(
         Event const &ev,
         const double tolerance
       ) {
         return massless_particles_onshell(ev.incoming(), tolerance)
           && massless_particles_onshell(ev.outgoing(), tolerance)
           && std::all_of(
             ev.decays().begin(), ev.decays().end(),
             [tolerance](auto const &decay) {
               return massless_particles_onshell(decay.second, tolerance);
             });
       }
 
       bool no_incoming_pt(Event const &ev, const double tolerance) {
         return std::all_of(
           ev.incoming().cbegin(), ev.incoming().end(),
           [tolerance](Particle const &p) {
             return std::abs(p.px()) < tolerance && std::abs(p.py()) < tolerance;
           });
       }
 
       bool is_invalid(Event const &ev, const double tolerance) {
         return !(
           charge_conserved(ev)
           && event_momentum_conserved(ev, tolerance)
           && no_incoming_pt(ev, tolerance)
           && all_massless_particles_onshell(ev, tolerance)
         );
       }
 
       // TODO: choose reasonable value or make configurable
       constexpr double TOLERANCE = 1e-3;
 
       bool incoming_are_partons(Event const &ev) {
         return std::all_of(
           ev.incoming().begin(), ev.incoming().end(),
           [](Particle const &p) { return is_parton(p); }
         );
       }
 
       bool known_outgoing(Event const &ev) {
         return std::all_of(
           ev.outgoing().begin(), ev.outgoing().end(),
           [](Particle const &p) {
             return is_parton(p)
               || p.type == pid::Higgs
               || std::abs(p.type) == pid::Wp
-              || p.type == pid::Z_photon_mix;
+              || p.type == pid::Z_photon_mix
+              || p.type == pid::Z;
           });
       }
 
       bool is_same_sign_WW(std::vector<Particle> const &particles) {
         return particles.size() == 2
           && std::abs(particles.front().type) == pid::Wp
           && particles.front().type == particles.back().type;
       }
 
       bool all_W_Zphoton_decay(Event const &ev) {
         auto const &out = ev.outgoing();
         for (std::size_t i = 0; i < out.size(); ++i) {
-          if (
-            (std::abs(out[i].type) == pid::Wp || out[i].type == pid::Z_photon_mix)
-            && ev.decays().count(i) == 0
-          ) {
+          const bool is_weak_boson = std::abs(out[i].type) == pid::Wp
+            || out[i].type == pid::Z_photon_mix
+            || out[i].type == pid::Z;
+          if (is_weak_boson && ev.decays().count(i) == 0) {
             return false;
           }
         }
         return true;
       }
 
       bool decay_known(
         Particle const &parent,
         std::vector<Particle> const &products
       ) {
         if (parent.type == pid::Higgs) return true;
         if (parent.type == pid::Z_photon_mix) return valid_Z_decay(products);
+        // If there is a Z we only allow decay to neutrinos,
+        // otherwise we are missing the Z/photon interference!
+        if (parent.type == pid::Z) return valid_Z_decay_to_neutrinos(products);
         if (std::abs(parent.type) == pid::Wp) {
           assert(charge(parent).denominator() == 1);
           return valid_W_decay(charge(parent).numerator(), products);
         }
         return false;
       }
 
       bool all_decays_known(Event const &ev) {
         return std::all_of(
           ev.decays().begin(), ev.decays().end(),
           [&ev](auto const &decay) {
             auto const &[parent, products] = decay;
             return decay_known(ev.outgoing()[parent], products);
           });
       }
 
       bool is_known_process_type(Event const &ev) {
         if (!incoming_are_partons(ev)) return false;
         if (!known_outgoing(ev)) return false;
         if (!all_W_Zphoton_decay(ev)) return false;
         if (!all_decays_known(ev)) return false;
         auto const bosons = filter_AWZH_bosons(ev.outgoing());
         if (bosons.size() > 2) return false;
         if (bosons.size() == 2 && !is_same_sign_WW(bosons)) {
           return false;
         }
         if (bosons.size() == 1 && bosons.front().type == pid::Higgs) {
           return !ev.jets().empty();
         }
         return ev.jets().size() >= 2;
       }
     }
 
     /**
      * \brief Checks for all event types
      * @param ev          Event
      * @returns           Event Type
      *
      */
     event_type::EventType classify(Event const & ev){
       using namespace event_type;
       if(is_invalid(ev, TOLERANCE)) return invalid;
       if(! is_known_process_type(ev)) return unknown;
 
       // initialise variables
       auto const & in = ev.incoming();
 
       // range for current checks
       auto begin_out = boost::make_filter_iterator(
         is_parton_or_higgs, cbegin(ev.outgoing()), cend(ev.outgoing())
       );
       auto rbegin_out = std::make_reverse_iterator(
         boost::make_filter_iterator(
           is_parton_or_higgs, cend(ev.outgoing()), cend(ev.outgoing())
         )
       );
 
       assert(std::distance(begin(in), end(in)) == 2);
       assert(std::distance(begin_out, rbegin_out.base()) >= 2);
       assert(std::is_sorted(begin_out, rbegin_out.base(), rapidity_less{}));
 
       auto const bosons{ filter_AWZH_bosons(ev.outgoing()) };
 
       // keep track of potential W couplings, at the end the sum should be 0
       int remaining_Wp = 0;
       int remaining_Wm = 0;
       for(auto const & boson : bosons){
           if(boson.type == ParticleID::Wp) ++remaining_Wp;
           else if(boson.type == ParticleID::Wm) ++remaining_Wm;
       }
 
       size_t final_type = VALID;
 
       // check forward impact factor
       int W_change = 0;
       final_type &= possible_impact_factors(
         in.front().type,
         begin_out, rbegin_out.base(),
         W_change, bosons, true );
       if( final_type == non_resummable )
         return non_resummable;
       if(W_change>0) remaining_Wp-=W_change;
       else if(W_change<0) remaining_Wm+=W_change;
 
       // check backward impact factor
       W_change = 0;
       final_type &= possible_impact_factors(
         in.back().type,
         rbegin_out, std::make_reverse_iterator(begin_out),
         W_change, bosons, false );
       if( final_type == non_resummable )
         return non_resummable;
       if(W_change>0) remaining_Wp-=W_change;
       else if(W_change<0) remaining_Wm+=W_change;
 
       // check central emissions
       W_change = 0;
       final_type &= possible_central(
         begin_out, rbegin_out.base(), W_change, bosons );
       if( final_type == non_resummable )
         return non_resummable;
       if(W_change>0) remaining_Wp-=W_change;
       else if(W_change<0) remaining_Wm+=W_change;
 
       // Check whether the right number of Ws are present
       if( remaining_Wp != 0 || remaining_Wm != 0 ) return non_resummable;
 
       // result has to be unique
       if( (final_type & (final_type-1)) != 0) return non_resummable;
 
       // check that each sub processes is implemented
       // (has to be done at the end)
       if( (final_type & ~implemented_types(bosons)) != 0 )
         return non_resummable;
 
       return static_cast<EventType>(final_type);
     }
     //@}
 
     Particle extract_particle(LHEF::HEPEUP const & hepeup, size_t i){
       auto id = static_cast<ParticleID>(hepeup.IDUP[i]);
       auto colour = is_parton(id)?hepeup.ICOLUP[i]:std::optional<Colour>();
       return { id,
                { hepeup.PUP[i][0], hepeup.PUP[i][1],
                  hepeup.PUP[i][2], hepeup.PUP[i][3] },
                colour
              };
     }
 
     bool is_decay_product(std::pair<int, int> const & mothers){
       if(mothers.first == 0) return false;
       return mothers.second == 0 || mothers.first == mothers.second;
     }
 
   } // namespace
 
   Event::EventData::EventData(LHEF::HEPEUP const & hepeup){
     parameters.central = EventParameters{
       hepeup.scales.mur, hepeup.scales.muf, hepeup.XWGTUP
     };
     size_t in_idx = 0;
     for (int i = 0; i < hepeup.NUP; ++i) {
       // skip decay products
       // we will add them later on, but we have to ensure that
       // the decayed particle is added before
       if(is_decay_product(hepeup.MOTHUP[i])) continue;
 
       auto particle = extract_particle(hepeup, i);
       // needed to identify mother particles for decay products
       particle.p.set_user_index(i+1);
 
       if(hepeup.ISTUP[i] == LHE_Status::in){
         if(in_idx > incoming.size()) {
           throw std::invalid_argument{
             "Event has too many incoming particles"
           };
         }
         incoming[in_idx++] = std::move(particle);
       }
       else outgoing.emplace_back(std::move(particle));
     }
 
     // add decay products
     for (int i = 0; i < hepeup.NUP; ++i) {
       if(!is_decay_product(hepeup.MOTHUP[i])) continue;
       const int mother_id = hepeup.MOTHUP[i].first;
       const auto mother = std::find_if(
           begin(outgoing), end(outgoing),
           [mother_id](Particle const & particle){
             return particle.p.user_index() == mother_id;
           }
       );
       if(mother == end(outgoing)){
         throw std::invalid_argument{"invalid decay product parent"};
       }
       const int mother_idx = std::distance(begin(outgoing), mother);
       assert(mother_idx >= 0);
       decays[mother_idx].emplace_back(extract_particle(hepeup, i));
     }
   }
 
   void Event::EventData::sort(){
     // sort particles
     std::sort(
         begin(incoming), end(incoming),
         [](Particle const & o1, Particle const & o2){return o1.p.pz()<o2.p.pz();}
     );
 
     auto old_outgoing = std::move(outgoing);
     std::vector<size_t> idx(old_outgoing.size());
     std::iota(idx.begin(), idx.end(), 0);
     std::sort(idx.begin(), idx.end(), [&old_outgoing](size_t i, size_t j){
       return old_outgoing[i].rapidity() < old_outgoing[j].rapidity();
     });
     outgoing.clear();
     outgoing.reserve(old_outgoing.size());
     for(size_t i: idx) {
       outgoing.emplace_back(std::move(old_outgoing[i]));
     }
 
     // find decays again
     if(!decays.empty()){
       auto old_decays = std::move(decays);
       decays.clear();
       for(size_t i=0; i<idx.size(); ++i) {
         auto decay = old_decays.find(idx[i]);
         if(decay != old_decays.end())
           decays.emplace(i, std::move(decay->second));
       }
       assert(old_decays.size() == decays.size());
     }
   }
 
   namespace {
     // use valid_X_decay to determine boson type
     ParticleID reconstruct_type(std::vector<Particle> const & progeny) {
       if(valid_W_decay(+1, progeny)) { return ParticleID::Wp; }
       if(valid_W_decay(-1, progeny)) { return ParticleID::Wm; }
       if(valid_Z_decay(progeny)) { return ParticleID::Z_photon_mix; }
 
       throw not_implemented{
         "final state with decay X -> "
           + name(progeny[0].type)
           + " + "
           + name(progeny[1].type)
       };
     }
 
     // reconstruct particle with explicit ParticleID
     Particle reconstruct_boson(
       std::vector<Particle> const & progeny,
       ParticleID const & type
     ) {
       Particle progenitor;
       progenitor.p = progeny[0].p + progeny[1].p;
       progenitor.type = type;
       return progenitor;
     }
 
     // reconstruct via call to reconstruct_type
     Particle reconstruct_boson(std::vector<Particle> const & progeny) {
       Particle progenitor {reconstruct_boson(progeny, reconstruct_type(progeny))};
       assert(is_AWZH_boson(progenitor));
       return progenitor;
     }
 
     using GroupedParticles = std::vector<std::vector<Particle> >;
     using Decay = std::pair<Particle, std::vector<Particle> >;
     using Decays = std::vector<Decay>;
 
     // return groups of reconstructable progeny
     std::vector<GroupedParticles> group_progeny(std::vector<Particle> & leptons) {
       /**
       Warning: The partition in to charged/neutral leptons is valid ONLY for WW.
       **/
       assert(leptons.size() == 4);
       auto const begin_neutrino = std::partition(
           begin(leptons), end(leptons),
           [](Particle const & p) {return !is_anyneutrino(p);}
       );
 
       std::vector<Particle> neutrinos (begin_neutrino, end(leptons));
       leptons.erase(begin_neutrino, end(leptons));
 
       if(leptons.size() != 2 || neutrinos.size() != 2) { return {}; }
       assert(leptons.size() == 2 && neutrinos.size() == 2);
 
       std::vector<GroupedParticles> valid_groupings;
 
       GroupedParticles candidate_grouping{{leptons[0], neutrinos[0]}, {leptons[1], neutrinos[1]}};
       if(valid_decay(candidate_grouping.front()) && valid_decay(candidate_grouping.back())) {
         valid_groupings.emplace_back(std::move(candidate_grouping));
       }
 
       candidate_grouping = {{leptons[1], neutrinos[0]}, {leptons[0], neutrinos[1]}};
       if(valid_decay(candidate_grouping.front()) && valid_decay(candidate_grouping.back())) {
         valid_groupings.emplace_back(std::move(candidate_grouping));
       }
 
       return valid_groupings;
     }
 
     // 'best' decay ordering measure
     double decay_measure(const Particle& reconstructed, EWConstants const & params) {
         ParticleProperties ref = params.prop(reconstructed.type);
         return std::abs(reconstructed.p.m() - ref.mass);
     }
 
     // decay_measure accumulated over decays
     double decay_measure(Decays const & decays, EWConstants const & params) {
       return
       std::accumulate(
         cbegin(decays), cend(decays), 0.,
         [&params] (double dm, Decay const & decay) -> double {
           return dm + decay_measure(decay.first, params);
         }
       );
     }
 
     // select best combination of decays for the event
     Decays select_decays
     (
       std::vector<Particle> & leptons,
       EWConstants const & ew_parameters
     ) {
       std::vector<GroupedParticles> groupings = group_progeny(leptons);
 
       std::vector<Decays> valid_decays;
       valid_decays.reserve(groupings.size());
 
       // Reconstruct all groupings
       for(GroupedParticles const & group : groupings) {
         Decays decays;
         for(auto const & progeny : group) {
           decays.emplace_back(make_pair(reconstruct_boson(progeny), progeny));
         }
         valid_decays.emplace_back(decays);
       }
       if (valid_decays.empty()) {
         throw not_implemented{"No supported intermediate reconstruction available"};
       }
       if (valid_decays.size() == 1) {
         return valid_decays[0];
       }
       // select decay with smallest decay_measure
       auto selected = std::min_element(cbegin(valid_decays), cend(valid_decays),
         [&ew_parameters] (auto const & d1, auto const & d2) -> bool {
           return decay_measure(d1, ew_parameters) < decay_measure(d2, ew_parameters);
         }
       );
       return *selected;
     }
   } // namespace
 
   void Event::EventData::reconstruct_intermediate(EWConstants const & ew_parameters) {
     auto const begin_leptons = std::partition(
         begin(outgoing), end(outgoing),
         [](Particle const & p) {return !is_anylepton(p);}
     );
     std::vector<Particle> leptons(begin_leptons, end(outgoing));
     outgoing.erase(begin_leptons, end(outgoing));
     if(leptons.empty()) { return; }  // nothing to do
     if(leptons.size() == 2) {
       outgoing.emplace_back(reconstruct_boson(leptons));
       std::sort(begin(leptons), end(leptons), type_less{});
       decays.emplace(outgoing.size()-1, std::move(leptons));
     }
     else if(leptons.size() == 4) {
       Decays valid_decays = select_decays(leptons, ew_parameters);
       for(auto &decay : valid_decays) {
         outgoing.emplace_back(decay.first);
         std::sort(begin(decay.second), end(decay.second), type_less{});
         decays.emplace(outgoing.size()-1, std::move(decay.second));
       }
     }
     else {
       throw not_implemented {
         std::to_string(leptons.size())
         + " leptons in the final state"
       };
     }
   }
 
   namespace {
     void repair_momentum(fastjet::PseudoJet & p, const double tolerance) {
       if(p.e() > 0. && p.m2() != 0. && (p.m2() < tolerance * tolerance)) {
         const double rescale = std::sqrt(p.modp() / p.e());
         const double e = p.e() * rescale;
         const double px = p.px() / rescale;
         const double py = p.py() / rescale;
         const double pz = p.pz() / rescale;
         p.reset(px, py, pz, e);
       }
     }
   }
 
   void Event::EventData::repair_momenta(const double tolerance) {
     for(auto & in: incoming) {
       if(is_massless(in)) {
         const double px = (std::abs(in.px()) < tolerance)?0.:in.px();
         const double py = (std::abs(in.py()) < tolerance)?0.:in.py();
         in.p.reset(px, py, in.p.pz(), in.p.e());
         repair_momentum(in.p, tolerance);
       }
     }
     for(auto & out: outgoing) {
       if(is_massless(out)) repair_momentum(out.p, tolerance);
     }
     for(auto & decay: decays) {
       for(auto & out: decay.second) {
         if(is_massless(out)) repair_momentum(out.p, tolerance);
       }
     }
   }
 
   Event Event::EventData::cluster(
       fastjet::JetDefinition const & jet_def, double const min_jet_pt
   ){
     sort();
     return Event{ std::move(incoming), std::move(outgoing), std::move(decays),
       std::move(parameters),
       jet_def, min_jet_pt
     };
   }
 
   Event::Event(
       std::array<Particle, 2> && incoming,
       std::vector<Particle> && outgoing,
       std::unordered_map<size_t, std::vector<Particle>> && decays,
       Parameters<EventParameters> && parameters,
       fastjet::JetDefinition const & jet_def,
       double const min_jet_pt
     ): incoming_{std::move(incoming)},
        outgoing_{std::move(outgoing)},
        decays_{std::move(decays)},
        parameters_{std::move(parameters)},
        cs_{ to_PseudoJet( filter_partons(outgoing_) ), jet_def },
        min_jet_pt_{min_jet_pt}
     {
       jets_ = sorted_by_rapidity(cs_.inclusive_jets(min_jet_pt_));
       assert(std::is_sorted(begin(outgoing_), end(outgoing_),
         rapidity_less{}));
       type_ = classify(*this);
     }
 
   namespace {
     //! check that Particles have a reasonable colour
     bool correct_colour(Particle const & part){
       ParticleID id{ part.type };
       if(!is_parton(id))
         return !part.colour;
 
       if(!part.colour)
         return false;
 
       Colour const & col{ *part.colour };
       if(is_quark(id))
         return col.first != 0 && col.second == 0;
       if(is_antiquark(id))
         return col.first == 0 && col.second != 0;
       assert(id==ParticleID::gluon);
       return col.first != 0 && col.second != 0 && col.first != col.second;
     }
 
     //! Connect parton to t-channel colour line & update the line
     //! returns false if connection not possible
     template<class OutIterator>
     bool try_connect_t(OutIterator const & it_part, Colour & line_colour){
       if( line_colour.first == it_part->colour->second ){
         line_colour.first = it_part->colour->first;
         return true;
       }
       if( line_colour.second == it_part->colour->first ){
         line_colour.second = it_part->colour->second;
         return true;
       }
       return false;
     }
 
     //! Connect parton to u-channel colour line & update the line
     //! returns false if connection not possible
     template<class OutIterator>
     bool try_connect_u(OutIterator & it_part, Colour & line_colour){
       auto it_next = std::next(it_part);
       if( try_connect_t(it_next, line_colour)
           && try_connect_t(it_part, line_colour)
       ){
         it_part=it_next;
         return true;
       }
       return false;
     }
   } // namespace
 
   bool Event::is_leading_colour() const {
     if( !correct_colour(incoming()[0]) || !correct_colour(incoming()[1]) )
       return false;
 
     Colour line_colour = *incoming()[0].colour;
     std::swap(line_colour.first, line_colour.second);
 
     // reasonable colour
     if(!std::all_of(outgoing().cbegin(), outgoing().cend(), correct_colour))
       return false;
 
     for(auto it_part = cbegin_partons(); it_part!=cend_partons(); ++it_part){
 
       switch (type()) {
       case event_type::FKL:
         if( !try_connect_t(it_part, line_colour) )
           return false;
         break;
       case event_type::unob:
       case event_type::qqbar_exb: {
         if( !try_connect_t(it_part, line_colour)
             // u-channel only allowed at impact factor
             && (std::distance(cbegin_partons(), it_part)!=0
                 || !try_connect_u(it_part, line_colour)))
           return false;
         break;
       }
       case event_type::unof:
       case event_type::qqbar_exf: {
         if( !try_connect_t(it_part, line_colour)
             // u-channel only allowed at impact factor
             && (std::distance(it_part, cend_partons())!=2
                 || !try_connect_u(it_part, line_colour)))
           return false;
         break;
       }
       case event_type::qqbar_mid:{
         auto it_next = std::next(it_part);
         if( !try_connect_t(it_part, line_colour)
             // u-channel only allowed at q-qbar/qbar-q pair
             && ( (   !(is_quark(*it_part) && is_antiquark(*it_next))
                   && !(is_antiquark(*it_part) && is_quark(*it_next)))
                 || !try_connect_u(it_part, line_colour))
           )
           return false;
         break;
       }
       default:
         throw std::logic_error{"unreachable"};
       }
 
       // no colour singlet exchange/disconnected diagram
       if(line_colour.first == line_colour.second)
         return false;
     }
 
     return (incoming()[1].colour->first == line_colour.first)
         && (incoming()[1].colour->second == line_colour.second);
   }
 
   namespace {
     //! connect incoming Particle to colour flow
     void connect_incoming(Particle & in, int & colour, int & anti_colour){
       in.colour = std::make_pair(anti_colour, colour);
       // gluon
       if(in.type == pid::gluon)
         return;
       if(in.type > 0){
         // quark
         assert(is_quark(in));
         in.colour->second = 0;
         colour*=-1;
         return;
       }
       // anti-quark
       assert(is_antiquark(in));
       in.colour->first = 0;
       anti_colour*=-1;
    }
 
     //! connect outgoing Particle to t-channel colour flow
     template<class OutIterator>
     void connect_tchannel(
         OutIterator & it_part, int & colour, int & anti_colour, RNG & ran
     ){
       assert(colour>0 || anti_colour>0);
       if(it_part->type == ParticleID::gluon){
         // gluon
         if(colour>0 && anti_colour>0){
           // on g line => connect to colour OR anti-colour (random)
           if(ran.flat() < 0.5){
             it_part->colour = std::make_pair(colour+2,colour);
             colour+=2;
           } else {
             it_part->colour = std::make_pair(anti_colour, anti_colour+2);
             anti_colour+=2;
           }
         } else if(colour > 0){
           // on q line => connect to available colour
             it_part->colour = std::make_pair(colour+2, colour);
             colour+=2;
         } else {
           assert(colour<0 && anti_colour>0);
           // on qbar line => connect to available anti-colour
           it_part->colour = std::make_pair(anti_colour, anti_colour+2);
           anti_colour+=2;
         }
       } else if(is_quark(*it_part)) {
         // quark
         assert(anti_colour>0);
         if(colour>0){
           // on g line => connect and remove anti-colour
           it_part->colour = std::make_pair(anti_colour, 0);
           anti_colour+=2;
           anti_colour*=-1;
         } else {
           // on qbar line => new colour
           colour*=-1;
           it_part->colour = std::make_pair(colour, 0);
         }
       } else if(is_antiquark(*it_part)) {
         // anti-quark
         assert(colour>0);
         if(anti_colour>0){
           // on g line => connect and remove colour
           it_part->colour = std::make_pair(0, colour);
           colour+=2;
           colour*=-1;
         } else {
           // on q line => new anti-colour
           anti_colour*=-1;
           it_part->colour = std::make_pair(0, anti_colour);
         }
       } else { // not a parton
         assert(!is_parton(*it_part));
         it_part->colour = {};
       }
     }
 
     //! connect to t- or u-channel colour flow
     template<class OutIterator>
     void connect_utchannel(
         OutIterator & it_part, int & colour, int & anti_colour, RNG & ran
     ){
       OutIterator it_first = it_part++;
       if(ran.flat()<.5) {// t-channel
         connect_tchannel(it_first, colour, anti_colour, ran);
         connect_tchannel(it_part, colour, anti_colour, ran);
       }
       else { // u-channel
         connect_tchannel(it_part, colour, anti_colour, ran);
         connect_tchannel(it_first, colour, anti_colour, ran);
       }
     }
   } // namespace
 
   bool Event::generate_colours(RNG & ran){
     // generate only for HEJ events
     if(!event_type::is_resummable(type()))
       return false;
     assert(std::is_sorted(
       begin(outgoing()), end(outgoing()), rapidity_less{}));
     assert(incoming()[0].pz() < incoming()[1].pz());
 
     // positive (anti-)colour -> can connect
     // negative (anti-)colour -> not available/used up by (anti-)quark
     int colour = COLOUR_OFFSET;
     int anti_colour = colour+1;
     // initialise first
     connect_incoming(incoming_[0], colour, anti_colour);
 
     // reset outgoing colours
     std::for_each(outgoing_.begin(), outgoing_.end(),
       [](Particle & part){ part.colour = {};});
 
     for(auto it_part = begin_partons(); it_part!=end_partons(); ++it_part){
         switch (type()) {
         // subleading can connect to t- or u-channel
         case event_type::unob:
         case event_type::qqbar_exb: {
           if( std::distance(begin_partons(), it_part)==0)
             connect_utchannel(it_part, colour, anti_colour, ran);
           else
             connect_tchannel(it_part, colour, anti_colour, ran);
           break;
         }
         case event_type::unof:
         case event_type::qqbar_exf: {
           if( std::distance(it_part, end_partons())==2)
             connect_utchannel(it_part, colour, anti_colour, ran);
           else
             connect_tchannel(it_part, colour, anti_colour, ran);
           break;
         }
         case event_type::qqbar_mid:{
           auto it_next = std::next(it_part);
           if( std::distance(begin_partons(), it_part)>0
               && std::distance(it_part, end_partons())>2
               && ( (is_quark(*it_part) && is_antiquark(*it_next))
                 || (is_antiquark(*it_part) && is_quark(*it_next)) )
           )
             connect_utchannel(it_part, colour, anti_colour, ran);
           else
             connect_tchannel(it_part, colour, anti_colour, ran);
           break;
         }
         default: // rest has to be t-channel
           connect_tchannel(it_part, colour, anti_colour, ran);
         }
     }
     // Connect last
     connect_incoming(incoming_[1], anti_colour, colour);
     assert(is_leading_colour());
     return true;
   } // generate_colours
 
   namespace {
     bool valid_parton(
       std::vector<fastjet::PseudoJet> const & jets,
       Particle const & parton, int const idx,
       double const soft_pt_regulator
     ){
       // TODO code overlap with PhaseSpacePoint::pass_extremal_cuts
       if(idx<0) return false;
       assert(static_cast<int>(jets.size())>=idx);
       auto const & jet{ jets[idx] };
       return (parton.p - jet).pt()/jet.pt() <= soft_pt_regulator;
     }
 
   } // namespace
 
   bool Event::valid_hej_state(double const soft_pt_regulator) const {
     using namespace event_type;
     const auto is_valid_parton = [&](Particle const & parton, int const jet_idx) {
       return valid_parton(jets(), parton, jet_idx, soft_pt_regulator);
     };
     if(!is_resummable(type()))
       return false;
 
     auto const & jet_indices{ particle_jet_indices() };
     auto jet_idx_begin{ jet_indices.cbegin() };
     auto jet_idx_end{  jet_indices.crbegin() };
 
     auto part_begin{ cbegin_partons() };
     auto part_end{  crbegin_partons() };
 
     if(!is_backward_g_to_h(*this)) {
       const int first_jet_idx = *jet_idx_begin;
       if(! is_valid_parton(*part_begin, first_jet_idx)) {
         return false;
       }
       ++part_begin;
       ++jet_idx_begin;
       // unob -> second parton in own jet
       if( type() & (unob | qqbar_exb) ){
         if(
           (*jet_idx_begin == first_jet_idx)
           || !is_valid_parton(*part_begin, *jet_idx_begin)
         ) {
           return false;
         }
         ++part_begin;
         ++jet_idx_begin;
       }
     }
     if(!is_forward_g_to_h(*this)) {
       const int last_jet_idx = *jet_idx_end;
       if(!is_valid_parton(*part_end, last_jet_idx)) {
         return false;
       }
       ++part_end;
       ++jet_idx_end;
       if( type() & (unof | qqbar_exf) ){
         if(
           (*jet_idx_end == last_jet_idx)
           || !is_valid_parton(*part_end, *jet_idx_end)
         ) {
           return false;
         }
         ++part_end;
         // ++jet_idx_end; // last check, we don't need idx_end afterwards
       }
     }
 
     if( type() & qqbar_mid ){
       // find qqbar pair
       auto begin_qqbar{ std::find_if( part_begin, part_end.base(),
         [](Particle const & part) -> bool {
           return part.type != ParticleID::gluon;
         }
       )};
       assert(begin_qqbar != part_end.base());
       long int qqbar_pos{ std::distance(part_begin, begin_qqbar) };
       assert(qqbar_pos >= 0);
       jet_idx_begin += qqbar_pos;
       const int next_jet_idx = *std::next(jet_idx_begin);
       if(
          (*jet_idx_begin == next_jet_idx)
         || ! is_valid_parton(*begin_qqbar, *jet_idx_begin)
         || ! is_valid_parton(*std::next(begin_qqbar), next_jet_idx)
       ) {
         return false;
       }
     }
     return true;
   }
 
   bool Event::valid_incoming() const{
     for(std::size_t i=0; i < incoming_.size(); ++i){
       if(!(HEJ::nearby_ep(std::abs(incoming_[i].pz()), incoming_[i].E(), TOL*incoming_[i].E())
            && (incoming_[i].pt()==0.)))
         return false;
     }
     return true;
   }
 
   Event::ConstPartonIterator Event::begin_partons() const {
     return cbegin_partons();
   }
   Event::ConstPartonIterator Event::cbegin_partons() const {
     return {HEJ::is_parton, cbegin(outgoing()), cend(outgoing())};
   }
 
   Event::ConstPartonIterator Event::end_partons() const {
     return cend_partons();
   }
   Event::ConstPartonIterator Event::cend_partons() const {
     return {HEJ::is_parton, cend(outgoing()), cend(outgoing())};
   }
 
   Event::ConstReversePartonIterator Event::rbegin_partons() const {
     return crbegin_partons();
   }
   Event::ConstReversePartonIterator Event::crbegin_partons() const {
     return std::reverse_iterator<ConstPartonIterator>( cend_partons() );
   }
 
   Event::ConstReversePartonIterator Event::rend_partons() const {
     return crend_partons();
   }
   Event::ConstReversePartonIterator Event::crend_partons() const {
     return std::reverse_iterator<ConstPartonIterator>( cbegin_partons() );
   }
 
   Event::PartonIterator Event::begin_partons() {
     return {HEJ::is_parton, begin(outgoing_), end(outgoing_)};
   }
 
   Event::PartonIterator Event::end_partons() {
     return {HEJ::is_parton, end(outgoing_), end(outgoing_)};
   }
 
   Event::ReversePartonIterator Event::rbegin_partons() {
     return std::reverse_iterator<PartonIterator>( end_partons() );
   }
 
   Event::ReversePartonIterator Event::rend_partons() {
     return std::reverse_iterator<PartonIterator>( begin_partons() );
   }
 
   namespace {
     void print_momentum(std::ostream & os, fastjet::PseudoJet const & part){
       constexpr int prec = 6;
       const std::streamsize orig_prec = os.precision();
       os <<std::scientific<<std::setprecision(prec) << "["
         <<std::setw(2*prec+1)<<std::right<< part.px() << ", "
         <<std::setw(2*prec+1)<<std::right<< part.py() << ", "
         <<std::setw(2*prec+1)<<std::right<< part.pz() << ", "
         <<std::setw(2*prec+1)<<std::right<< part.E() << "]"<< std::fixed;
       os.precision(orig_prec);
     }
 
     void print_colour(std::ostream & os, std::optional<Colour> const & col){
       constexpr int width = 3;
       if(!col)
         os << "(no color)"; // American spelling for better alignment
       else
         os << "("  <<std::setw(width)<<std::right<< col->first
            << ", " <<std::setw(width)<<std::right<< col->second << ")";
     }
   } // namespace
 
   std::ostream& operator<<(std::ostream & os, Event const & ev){
     constexpr int prec = 4;
     constexpr int wtype = 3; // width for types
     const std::streamsize orig_prec = os.precision();
     os <<std::setprecision(prec)<<std::fixed;
     os << "########## " << name(ev.type()) << " ##########" << std::endl;
     os << "Incoming particles:\n";
     for(auto const & in: ev.incoming()){
       os <<std::setw(wtype)<< in.type << ": ";
       print_colour(os, in.colour);
       os << " ";
       print_momentum(os, in.p);
       os << std::endl;
     }
     os << "\nOutgoing particles: " << ev.outgoing().size() << "\n";
     for(auto const & out: ev.outgoing()){
       os <<std::setw(wtype)<< out.type << ": ";
       print_colour(os, out.colour);
       os << " ";
       print_momentum(os, out.p);
       os << " => rapidity="
         <<std::setw(2*prec-1)<<std::right<< out.rapidity() << std::endl;
     }
     os << "\nForming Jets: " << ev.jets().size() << "\n";
     for(auto const & jet: ev.jets()){
       print_momentum(os, jet);
       os << " => rapidity="
         <<std::setw(2*prec-1)<<std::right<< jet.rapidity() << std::endl;
     }
     if(!ev.decays().empty() ){
       os << "\nDecays: " << ev.decays().size() << "\n";
       for(auto const & decay: ev.decays()){
         os <<std::setw(wtype)<< ev.outgoing()[decay.first].type
           << " (" << decay.first << ") to:\n";
         for(auto const & out: decay.second){
           os <<"  "<<std::setw(wtype)<< out.type << ": ";
           print_momentum(os, out.p);
           os << " => rapidity="
             <<std::setw(2*prec-1)<<std::right<< out.rapidity() << std::endl;
         }
       }
 
     }
     os << std::defaultfloat;
     os.precision(orig_prec);
     return os;
   }
 
   std::string to_string(Event const & ev){
     std::stringstream ss;
     ss << ev;
     return ss.str();
   }
 
   double shat(Event const & ev){
     return (ev.incoming()[0].p + ev.incoming()[1].p).m2();
   }
 
   LHEF::HEPEUP to_HEPEUP(Event const & event, LHEF::HEPRUP * heprup){
     LHEF::HEPEUP result;
     result.heprup = heprup;
     result.weights = {{event.central().weight, nullptr}};
     for(auto const & var: event.variations()){
       result.weights.emplace_back(var.weight, nullptr);
     }
     size_t num_particles = event.incoming().size() + event.outgoing().size();
     for(auto const & decay: event.decays()) num_particles += decay.second.size();
     result.NUP = num_particles;
     // the following entries are pretty much meaningless
     result.IDPRUP = event.type();  // event type
     result.AQEDUP = 1./128.;  // alpha_EW
     //result.AQCDUP = 0.118 // alpha_QCD
     // end meaningless part
     result.XWGTUP = event.central().weight;
     result.SCALUP = event.central().muf;
     result.scales.muf = event.central().muf;
     result.scales.mur = event.central().mur;
     result.scales.SCALUP = event.central().muf;
     result.pdfinfo.p1 = event.incoming().front().type;
     result.pdfinfo.p2 = event.incoming().back().type;
     result.pdfinfo.scale = event.central().muf;
 
     result.IDUP.reserve(num_particles);   // PID
     result.ISTUP.reserve(num_particles);  // status (in, out, decay)
     result.PUP.reserve(num_particles);    // momentum
     result.MOTHUP.reserve(num_particles); // index mother particle
     result.ICOLUP.reserve(num_particles); // colour
     // incoming
     std::array<Particle, 2> incoming{ event.incoming() };
     // First incoming should be positive pz according to LHE standard
     // (or at least most (everyone?) do it this way, and Pythia assumes it)
     if(incoming[0].pz() < incoming[1].pz())
       std::swap(incoming[0], incoming[1]);
     for(Particle const & in: incoming){
       result.IDUP.emplace_back(in.type);
       result.ISTUP.emplace_back(LHE_Status::in);
       result.PUP.push_back({in.p[0], in.p[1], in.p[2], in.p[3], in.p.m()});
       result.MOTHUP.emplace_back(0, 0);
       assert(in.colour);
       result.ICOLUP.emplace_back(*in.colour);
     }
     // outgoing
     for(size_t i = 0; i < event.outgoing().size(); ++i){
       Particle const & out = event.outgoing()[i];
       result.IDUP.emplace_back(out.type);
       const int status = event.decays().count(i) != 0u
                           ?LHE_Status::decay
                           :LHE_Status::out;
       result.ISTUP.emplace_back(status);
       result.PUP.push_back({out.p[0], out.p[1], out.p[2], out.p[3], out.p.m()});
       result.MOTHUP.emplace_back(1, 2);
       if(out.colour)
         result.ICOLUP.emplace_back(*out.colour);
       else{
         result.ICOLUP.emplace_back(std::make_pair(0,0));
       }
     }
     // decays
     for(auto const & decay: event.decays()){
       for(auto const & out: decay.second){
         result.IDUP.emplace_back(out.type);
         result.ISTUP.emplace_back(LHE_Status::out);
         result.PUP.push_back({out.p[0], out.p[1], out.p[2], out.p[3], out.p.m()});
         const size_t mother_idx = 1 + event.incoming().size() + decay.first;
         result.MOTHUP.emplace_back(mother_idx, mother_idx);
         result.ICOLUP.emplace_back(0,0);
       }
     }
 
     assert(result.ICOLUP.size() == num_particles);
     static constexpr double unknown_spin = 9.;     //per Les Houches accord
     result.VTIMUP = std::vector<double>(num_particles, unknown_spin);
     result.SPINUP = result.VTIMUP;
     return result;
   }
 
 } // namespace HEJ
diff --git a/src/MatrixElement.cc b/src/MatrixElement.cc
index 1044a74..b291815 100644
--- a/src/MatrixElement.cc
+++ b/src/MatrixElement.cc
@@ -1,2954 +1,2954 @@
 /**
  *  \authors   The HEJ collaboration (see AUTHORS for details)
  *  \date      2019-2023
  *  \copyright GPLv2 or later
  */
 #include "HEJ/MatrixElement.hh"
 
 #include <algorithm>
 #include <cassert>
 #include <cmath>
 #include <cstddef>
 #include <cstdlib>
 #include <iterator>
 #include <limits>
 #include <unordered_map>
 #include <utility>
 
 #include "fastjet/PseudoJet.hh"
 
 #include "HEJ/ConfigFlags.hh"
 #include "HEJ/Constants.hh"
 #include "HEJ/EWConstants.hh"
 #include "HEJ/Event.hh"
 #include "HEJ/HiggsCouplingSettings.hh"
 #include "HEJ/Hjets.hh"
 #include "HEJ/LorentzVector.hh"
 #include "HEJ/PDG_codes.hh"
 #include "HEJ/Particle.hh"
 #include "HEJ/WWjets.hh"
 #include "HEJ/Wjets.hh"
 #include "HEJ/Zjets.hh"
 #include "HEJ/event_types.hh"
 #include "HEJ/exceptions.hh"
 #include "HEJ/jets.hh"
 #include "HEJ/utility.hh"
 
 namespace HEJ {
   namespace {
 
     // Colour acceleration multiplier for gluons
     // see eq:K_g in developer manual
     double K_g(double p1minus, double paminus) {
       return 1./2.*(p1minus/paminus + paminus/p1minus)*(C_A - 1./C_A) + 1./C_A;
     }
     double K_g(
       CLHEP::HepLorentzVector const & pout,
       CLHEP::HepLorentzVector const & pin
     ) {
       if(pin.z() > 0) return K_g(pout.plus(), pin.plus());
       return K_g(pout.minus(), pin.minus());
     }
 
     // Colour acceleration multiplier for quarks
     // see eq:K_q in developer manual
     constexpr double K_q = C_F;
 
     // Colour acceleration multipliers
     double K(
         ParticleID type,
         CLHEP::HepLorentzVector const & pout,
         CLHEP::HepLorentzVector const & pin
     ){
       if(type == pid::gluon) return K_g(pout, pin);
       return K_q;
     }
   } // namespace
 
   double MatrixElement::omega0(
       double alpha_s, double mur,
       fastjet::PseudoJet const & q_j
   ) const {
     const double lambda = param_.regulator_lambda;
     const double result = - alpha_s*N_C/M_PI*std::log(q_j.perp2()/(lambda*lambda));
     if(! param_.log_correction) return result;
     return (
         1. + alpha_s/(4.*M_PI)*BETA0*std::log(mur*mur/(q_j.perp()*lambda))
     )*result;
   }
 
   Weights MatrixElement::operator()(Event const & event) const {
     std::vector <double> tree_kin_part=tree_kin(event);
     std::vector <Weights> virtual_part=virtual_corrections(event);
     if(tree_kin_part.size() != virtual_part.size()) {
       throw std::logic_error("tree and virtuals have different sizes");
     }
     Weights sum = Weights{0., std::vector<double>(event.variations().size(), 0.)};
     for(size_t i=0; i<tree_kin_part.size(); ++i) {
       sum += tree_kin_part.at(i)*virtual_part.at(i);
     }
     return tree_param(event)*sum;
   }
 
   Weights MatrixElement::tree(Event const & event) const {
     std::vector <double> tree_kin_part=tree_kin(event);
     double sum = 0.;
     for(double i : tree_kin_part) {
       sum += i;
     }
     return tree_param(event)*sum;
   }
 
   Weights MatrixElement::tree_param(Event const & event) const {
     if(! is_resummable(event.type())) {
       return Weights{0., std::vector<double>(event.variations().size(), 0.)};
     }
     Weights result;
     // only compute once for each renormalisation scale
     std::unordered_map<double, double> known;
     result.central = tree_param(event, event.central().mur);
     known.emplace(event.central().mur, result.central);
     for(auto const & var: event.variations()) {
       const auto ME_it = known.find(var.mur);
       if(ME_it == end(known)) {
         const double wt = tree_param(event, var.mur);
         result.variations.emplace_back(wt);
         known.emplace(var.mur, wt);
       }
       else {
         result.variations.emplace_back(ME_it->second);
       }
     }
     return result;
   }
 
   std::vector<Weights> MatrixElement::virtual_corrections(Event const & event) const {
     if(!event.valid_hej_state(param_.soft_pt_regulator)) {
       return {Weights{0., std::vector<double>(event.variations().size(), 0.)}};
     }
     // only compute once for each renormalisation scale
     std::unordered_map<double, std::vector<double> > known_vec;
     std::vector<double> central_vec=virtual_corrections(event, event.central().mur);
     known_vec.emplace(event.central().mur, central_vec);
     for(auto const & var: event.variations()) {
       const auto ME_it = known_vec.find(var.mur);
       if(ME_it == end(known_vec)) {
         known_vec.emplace(var.mur, virtual_corrections(event, var.mur));
       }
     }
     // At this stage known_vec contains one vector of virtual corrections for each mur value
     // Now put this into a vector of Weights
     std::vector<Weights> result_vec;
     for(size_t i=0; i<central_vec.size(); ++i) {
       Weights result;
       result.central = central_vec.at(i);
       for(auto const & var: event.variations()) {
         const auto ME_it = known_vec.find(var.mur);
         result.variations.emplace_back(ME_it->second.at(i));
       }
       result_vec.emplace_back(result);
     }
     return result_vec;
   }
 
   template<class InputIterator>
   double MatrixElement::virtual_corrections_no_interference(
       InputIterator begin_parton, InputIterator end_parton,
       fastjet::PseudoJet & q,
       const double mur
   ) const{
     const double alpha_s = alpha_s_(mur);
 
     double exponent = 0.;
     for(auto parton_it = begin_parton; parton_it != end_parton; ++parton_it){
       exponent += omega0(alpha_s, mur, q)*(
           (parton_it+1)->rapidity() - parton_it->rapidity()
       );
       q -= (parton_it+1)->p;
     }
 
     return exponent;
   }
 
   template<class InputIterator>
   std::vector <double> MatrixElement::virtual_corrections_interference(
       InputIterator begin_parton, InputIterator end_parton,
       fastjet::PseudoJet & q_t,
       fastjet::PseudoJet & q_b,
       const double mur
   ) const{
     const double alpha_s = alpha_s_(mur);
 
     double sum_top = 0.;
     double sum_bot = 0.;
     double sum_mix = 0.;
     for(auto parton_it = begin_parton; parton_it != end_parton; ++parton_it){
       const double dy = (parton_it+1)->rapidity() - parton_it->rapidity();
       const double tmp_top = omega0(alpha_s, mur, q_t) * dy;
       const double tmp_bot = omega0(alpha_s, mur, q_b) * dy;
       sum_top += tmp_top;
       sum_bot += tmp_bot;
       sum_mix += (tmp_top + tmp_bot) / 2.;
       q_t -= (parton_it+1)->p;
       q_b -= (parton_it+1)->p;
     }
 
     return {sum_top, sum_bot, sum_mix};
   }
 
   double MatrixElement::virtual_corrections_W(
       Event const & event,
       const double mur,
       Particle const & WBoson
   ) const{
     auto const & in = event.incoming();
     const auto partons = filter_partons(event.outgoing());
     fastjet::PseudoJet const & pa = in.front().p;
 #ifndef NDEBUG
     fastjet::PseudoJet const & pb = in.back().p;
     double const norm = (in.front().p + in.back().p).E();
 #endif
 
     assert(std::is_sorted(partons.begin(), partons.end(), rapidity_less{}));
     assert(partons.size() >= 2);
     assert(pa.pz() < pb.pz());
 
     fastjet::PseudoJet q = pa - partons[0].p;
 
     auto first_idx = cbegin(partons);
     auto last_idx  = cend(partons) - 1;
 
 #ifndef NDEBUG
     bool wc = true;
 #endif
 
     // With extremal qqbar or unordered gluon outside the extremal
     // partons then it is not part of the FKL ladder and does not
     // contribute to the virtual corrections. W emitted from the
     // most backward leg must be taken into account in t-channel
     if (event.type() == event_type::unob) {
       q -= partons[1].p;
       ++first_idx;
       if (in[0].type != partons[1].type ){
         q -= WBoson.p;
 #ifndef NDEBUG
         wc=false;
 #endif
       }
     }
     else if (event.type() == event_type::qqbar_exb) {
       q -= partons[1].p;
       ++first_idx;
       if (std::abs(partons[0].type) != std::abs(partons[1].type)){
         q -= WBoson.p;
 #ifndef NDEBUG
         wc=false;
 #endif
       }
     }
     else {
       if(event.type() == event_type::unof
          || event.type() == event_type::qqbar_exf){
         --last_idx;
       }
       if (in[0].type != partons[0].type ){
         q -= WBoson.p;
 #ifndef NDEBUG
         wc=false;
 #endif
       }
     }
 
     auto first_idx_qqbar = last_idx;
     auto last_idx_qqbar  = last_idx;
 
     bool wqq = false;
 
     //if qqbarMid event, virtual correction do not occur between qqbar pair.
     if(event.type() == event_type::qqbar_mid){
       const auto backquark = std::find_if(
         begin(partons) + 1, end(partons) - 1 ,
         [](Particle const & s){ return (s.type != pid::gluon); }
       );
       assert(backquark!=end(partons)-1 && (backquark+1)->type!=pid::gluon);
       if(std::abs(backquark->type) != std::abs((backquark+1)->type)) {
         wqq=true;
 #ifndef NDEBUG
         wc=false;
 #endif
       }
       last_idx = backquark;
       first_idx_qqbar = last_idx+1;
     }
 
     double exponent = virtual_corrections_no_interference(first_idx, last_idx, q, mur);
 
     if(last_idx != first_idx_qqbar) {
       q -= (last_idx+1)->p;
       if(wqq) q -= WBoson.p;
       exponent += virtual_corrections_no_interference(first_idx_qqbar, last_idx_qqbar, q, mur);
     }
 
 #ifndef NDEBUG
     if (wc) q -= WBoson.p;
     assert(
         nearby(q, -1*pb, norm)
         || is_AWZH_boson(partons.back().type)
         || event.type() == event_type::unof
         || event.type() == event_type::qqbar_exf
     );
 #endif
 
     if(param_.nlo.enabled) {
       double nlo_virtual = 1.;
       // Only apply virtual corrections to a nlo order event.
       if(partons.size() == param_.nlo.nj) nlo_virtual += exponent;
       return nlo_virtual;
     }
 
     return std::exp(exponent);
   }
 
 
 
   std::vector <double> MatrixElement::virtual_corrections_WW(
       Event const & event,
       const double mur
   ) const{
     auto const & in = event.incoming();
     const auto partons = filter_partons(event.outgoing());
     fastjet::PseudoJet const & pa = in.front().p;
 #ifndef NDEBUG
     fastjet::PseudoJet const & pb = in.back().p;
 #endif
 
     assert(std::is_sorted(partons.begin(), partons.end(), rapidity_less{}));
     assert(partons.size() >= 2);
     assert(pa.pz() < pb.pz());
     assert(event.decays().size() == 2);
 
     std::vector<fastjet::PseudoJet> plbar;
     std::vector<fastjet::PseudoJet> pl;
 
     for(auto const & decay_pair : event.decays()) {
       auto const decay = decay_pair.second;
       if(decay.at(0).type < 0) {
         plbar.emplace_back(decay.at(0).p);
         pl   .emplace_back(decay.at(1).p);
       }
       else {
         pl   .emplace_back(decay.at(0).p);
         plbar.emplace_back(decay.at(1).p);
       }
     }
 
     fastjet::PseudoJet q_t = pa - partons[0].p - pl[0] - plbar[0];
     fastjet::PseudoJet q_b = pa - partons[0].p - pl[1] - plbar[1];
 
     auto const begin_parton = cbegin(partons);
     auto const end_parton = cend(partons) - 1;
 
     auto res = virtual_corrections_interference(begin_parton, end_parton, q_t, q_b, mur);
 
     if(param_.nlo.enabled) {
       if(partons.size() > param_.nlo.nj) return std::vector<double>(1., res.size());
       assert(partons.size() == param_.nlo.nj);
       for(double & virt: res) virt += 1.;
     } else {
       for(double & virt: res) virt = exp(virt);
     }
 
     return res;
   }
 
   // Virtual corrections for Z processes without interference (only one contribution)
   double MatrixElement::virtual_corrections_Z_single(
       Event const & event,
       const double mur,
       Particle const & ZBoson,
       const bool emit_fwd
   ) const{
     auto const & in = event.incoming();
     const auto partons = filter_partons(event.outgoing());
     fastjet::PseudoJet const & pa = in.front().p;
 #ifndef NDEBUG
     fastjet::PseudoJet const & pb = in.back().p;
 #endif
 
     assert(std::is_sorted(partons.begin(), partons.end(), rapidity_less{}));
     assert(partons.size() >= 2);
     assert(pa.pz() < pb.pz());
 
     // If the Z is emitted from forward leg or central qqbar, don't subtract the Z momentum from first q
     fastjet::PseudoJet q;
     if(emit_fwd || event.type()==event_type::central_qqbar) {
       q = pa - partons[0].p;
     } else {
       q = pa - partons[0].p - ZBoson.p;
     }
 
     auto first_idx = cbegin(partons);
     auto last_idx  = cend(partons) - 1;
 
     // for uno/exqqbar the two extremal partons do not contribute to the virtual corrections
     if (event.type() == event_type::unob
         || event.type() == event_type::qqbar_exb) {
       // unordered gluon or first quark is partons[0] and is already subtracted
       // partons[1] is the backward quark (uno case) or the second quark (exqqbar case)
       q -= partons[1].p;
       ++first_idx;
     } else if (event.type() == event_type::unof
                || event.type() == event_type::qqbar_exf) {
       // end sum at next to last parton
       --last_idx;
     }
 
     // if central qqbar event, virtual correction do not occur between qqbar pair
     auto first_idx_qqbar = last_idx;
     auto last_idx_qqbar  = last_idx;
     if(event.type() == event_type::central_qqbar){
       const auto backquark = std::find_if(
         begin(partons) + 1, end(partons) - 1 ,
         [](Particle const & s){ return (s.type != pid::gluon); }
       );
       assert(backquark!=end(partons)-1 && (backquark+1)->type!=pid::gluon);
       last_idx = backquark;
       first_idx_qqbar = last_idx+1;
     }
 
     double exponent = virtual_corrections_no_interference(first_idx, last_idx, q, mur);
 
     if(last_idx != first_idx_qqbar) {
       q -= (last_idx+1)->p;
       q -= ZBoson.p;
       exponent += virtual_corrections_no_interference(first_idx_qqbar, last_idx_qqbar, q, mur);
     }
 
     if(param_.nlo.enabled) {
       double nlo_virtual = 1.;
       // Only apply virtual corrections to a nlo order event.
       if(partons.size() == param_.nlo.nj) nlo_virtual += exponent;
       return nlo_virtual;
     }
 
     return exp(exponent);
   }
 
   // Virtual corrections for Z processes with 2 interfering contributions
   // Returns 3 values (2 squares + 1 interference term)
   std::vector<double> MatrixElement::virtual_corrections_Z_double(
       Event const & event,
       const double mur,
       Particle const & ZBoson
   ) const{
     auto const & in = event.incoming();
     const auto partons = filter_partons(event.outgoing());
     fastjet::PseudoJet const & pa = in.front().p;
 #ifndef NDEBUG
     fastjet::PseudoJet const & pb = in.back().p;
 #endif
 
     assert(std::is_sorted(partons.begin(), partons.end(), rapidity_less{}));
     assert(partons.size() >= 2);
     assert(pa.pz() < pb.pz());
 
     fastjet::PseudoJet q_t;
     if(event.type() == event_type::central_qqbar && is_gluon(in.front().type)) {
       // gq initiated central qqbar event -> "top" emission from qqbar
       q_t = pa - partons[0].p;
     } else {
       // top emission from top quark leg
       q_t = pa - partons[0].p - ZBoson.p;
     }
     fastjet::PseudoJet q_b = pa - partons[0].p;
 
     auto first_idx = cbegin(partons);
     auto last_idx = cend(partons) - 1;
 
     // for uno/exqqbar the two extremal partons do not contribute to the virtual corrections
     if (event.type() == event_type::unob
         || event.type() == event_type::qqbar_exb) {
       // unordered gluon or first quark is partons[0] and is already subtracted
       // partons[1] is the backward quark (uno case) or the second quark (exqqbar case)
       q_t -= partons[1].p;
       q_b -= partons[1].p;
       ++first_idx;
     } else if (event.type() == event_type::unof
                || event.type() == event_type::qqbar_exf) {
       // end sum at next to last parton
       --last_idx;
     }
 
     // if central qqbar event, virtual correction do not occur between qqbar pair
     auto first_idx_qqbar = last_idx;
     auto last_idx_qqbar  = last_idx;
     if(event.type() == event_type::central_qqbar){
       const auto backquark = std::find_if(
         begin(partons) + 1, end(partons) - 1 ,
         [](Particle const & s){ return (s.type != pid::gluon); }
       );
       assert(backquark!=end(partons)-1 && (backquark+1)->type!=pid::gluon);
       last_idx = backquark;
       first_idx_qqbar = last_idx+1;
     }
 
     auto res = virtual_corrections_interference(first_idx, last_idx, q_t, q_b, mur);
 
     if(last_idx != first_idx_qqbar) {
       q_t -= (last_idx+1)->p;
       q_b -= (last_idx+1)->p;
 
       if(is_gluon(in.front().type)) {
         // "top" emission from qqbar, "bot" emission from bottom quark leg
         q_t -= ZBoson.p;
       } else {
         // "top" emission from top quark leg, "bot" emission from qqbar
         q_b -= ZBoson.p;
       }
 
       auto res_2 = virtual_corrections_interference(first_idx_qqbar, last_idx_qqbar, q_t, q_b, mur);
 
       for(std::size_t i=0; i<res.size(); ++i){
         res[i] += res_2[i];
       }
     }
 
     if(param_.nlo.enabled) {
       if(partons.size() > param_.nlo.nj) return std::vector<double>(1., res.size());
       assert(partons.size() == param_.nlo.nj);
       for(double & virt: res) virt += 1.;
     } else {
       for(double & virt: res) virt = exp(virt);
     }
 
     return res;
   }
 
   // Virtual corrections for Z processes with 3 interfering contributions
   // Returns 6 values (3 squares + 3 interference terms)
   std::vector <double> MatrixElement::virtual_corrections_Z_triple(
       Event const & event,
       const double mur,
       Particle const & ZBoson
   ) const{
     assert(event.type() == event_type::central_qqbar);
 
     auto const & in = event.incoming();
     const auto partons = filter_partons(event.outgoing());
     fastjet::PseudoJet const & pa = in.front().p;
 #ifndef NDEBUG
     fastjet::PseudoJet const & pb = in.back().p;
 #endif
 
     assert(std::is_sorted(partons.begin(), partons.end(), rapidity_less{}));
     assert(partons.size() >= 2);
     assert(pa.pz() < pb.pz());
 
     enum emission_site {top, mid, bot};
 
     fastjet::PseudoJet q_t = pa - partons[0].p - ZBoson.p;
     fastjet::PseudoJet q_b = pa - partons[0].p;
 
     auto first_idx = cbegin(partons);
     auto last_idx = cend(partons) - 1;
 
     auto first_idx_qqbar = last_idx;
     auto last_idx_qqbar  = last_idx;
 
     const auto backquark = std::find_if(
       begin(partons) + 1, end(partons) - 1 ,
       [](Particle const & s){ return (s.type != pid::gluon); }
     );
     assert(backquark!=end(partons)-1 && (backquark+1)->type!=pid::gluon);
     last_idx = backquark;
     first_idx_qqbar = last_idx+1;
 
     // here q[bot] = q[mid], thus we only need to evaluate virtual_corrections_interference[top][mid]
     const auto res_1_top_mid = virtual_corrections_interference(first_idx, last_idx, q_t, q_b, mur);
 
     double res_tmp[3][3];
     res_tmp[top][top] = res_1_top_mid.at(0);
     res_tmp[mid][mid] = res_1_top_mid.at(1);
     res_tmp[bot][bot] = res_tmp[mid][mid];
 
     res_tmp[top][mid] = res_1_top_mid.at(2);
     res_tmp[top][bot] = res_tmp[top][mid];
     res_tmp[mid][bot] = res_tmp[mid][mid];
 
     if(last_idx != first_idx_qqbar) {
       q_t -= (last_idx+1)->p;
       q_b -= (last_idx+1)->p;
 
       // here q[mid] = q[top], thus we only need to evaluate virtual_corrections_interference[top][bot]
       const auto res_2_top_bot = virtual_corrections_interference(first_idx_qqbar, last_idx_qqbar,
                                                                   q_t, q_b, mur);
 
       res_tmp[top][top] += res_2_top_bot.at(0);
       res_tmp[mid][mid] += res_2_top_bot.at(0); // same as [top][top]
       res_tmp[bot][bot] += res_2_top_bot.at(1);
 
       res_tmp[top][mid] += res_2_top_bot.at(0); // same as [top][top]
       res_tmp[top][bot] += res_2_top_bot.at(2);
       res_tmp[mid][bot] += res_2_top_bot.at(2); // same as [top][bot]
     }
 
     std::vector<double> res = {res_tmp[top][top], res_tmp[mid][mid], res_tmp[bot][bot],
                                res_tmp[top][mid], res_tmp[top][bot], res_tmp[mid][bot]};
 
     if(param_.nlo.enabled) {
       if(partons.size() > param_.nlo.nj) return std::vector<double>(1., res.size());
       assert(partons.size() == param_.nlo.nj);
       for(double & virt: res) virt += 1.;
     } else {
       for(double & virt: res) virt = exp(virt);
     }
 
     return res;
   }
 
   std::vector<double> MatrixElement::virtual_corrections_Z(
       Event const & event,
       const double mur,
       Particle const & ZBoson
   ) const{
     using namespace event_type;
     auto const & in = event.incoming();
 
     if(event.type() == central_qqbar) {
       if(is_gluon(in.front().type)) {
         if(is_gluon(in.back().type)) {
           // gg event
           return {virtual_corrections_Z_single(event, mur, ZBoson, false)};
         } else {
           // gq event
           return virtual_corrections_Z_double(event, mur, ZBoson);
         }
       } else {
         if(is_gluon(in.back().type)) {
           // qg event
           return virtual_corrections_Z_double(event, mur, ZBoson);
         } else {
           // qq event
           return virtual_corrections_Z_triple(event, mur, ZBoson);
         }
       }
     }
 
     if(event.type() == qqbar_exb && is_gluon(in.back().type)) {
       // gg event, emission from backward leg
       return {virtual_corrections_Z_single(event, mur, ZBoson, false)};
     }
 
     if(event.type() == qqbar_exf && is_gluon(in.front().type)) {
       // gg event, emission from forward leg
       return {virtual_corrections_Z_single(event, mur, ZBoson, true)};
     }
 
     if(event.type() == FKL || event.type() == unob || event.type() == unof) {
       if(is_gluon(in.back().type)) {
         // qg event, emission from backward leg
         return {virtual_corrections_Z_single(event, mur, ZBoson, false)};
       }
       if(is_gluon(in.front().type)) {
         // gq event, emission from forward leg
         return {virtual_corrections_Z_single(event, mur, ZBoson, true)};
       }
     }
 
     // qq initiated FKL/uno or qg/gq initiated exqqbar
     return virtual_corrections_Z_double(event, mur, ZBoson);
   }
 
   std::vector<double> MatrixElement::virtual_corrections(
       Event const & event,
       const double mur
   ) const{
     auto const & in = event.incoming();
     auto const & out = event.outgoing();
     fastjet::PseudoJet const & pa = in.front().p;
 #ifndef NDEBUG
     fastjet::PseudoJet const & pb = in.back().p;
     double const norm = (in.front().p + in.back().p).E();
 #endif
 
     std::vector<Particle> bosons = filter_AWZH_bosons(out);
 
     if(event.jets().size() != param_.nlo.nj && param_.nlo.enabled) {
         throw std::logic_error{
           "Input event has number of jets different to stated NLO "
           "input in config file: " + std::to_string(event.jets().size())
           + " vs "  +std::to_string(param_.nlo.nj) + "\n"
         };
     }
     if(bosons.size() > 2) {
       throw not_implemented("Emission of >2 bosons is unsupported");
     }
 
     if(bosons.size() == 2) {
       if(bosons[0].type == pid::Wp && bosons[1].type == pid::Wp) {
         return virtual_corrections_WW(event, mur);
       }
       else if(bosons[0].type == pid::Wm && bosons[1].type == pid::Wm) {
         return virtual_corrections_WW(event, mur);
       }
       throw not_implemented("Emission of bosons of unsupported type");
     }
 
     if(bosons.size() == 1) {
       const auto AWZH_boson = bosons[0];
 
       if(std::abs(AWZH_boson.type) == pid::Wp){
         return {virtual_corrections_W(event, mur, AWZH_boson)};
       }
 
-      if(AWZH_boson.type == pid::Z_photon_mix){
+      if(AWZH_boson.type == pid::Z_photon_mix || AWZH_boson.type == pid::Z){
         return virtual_corrections_Z(event, mur, AWZH_boson);
       }
     }
 
     assert(std::is_sorted(out.begin(), out.end(), rapidity_less{}));
     assert(out.size() >= 2);
     assert(pa.pz() < pb.pz());
 
     fastjet::PseudoJet q = pa - out[0].p;
 
     auto first_idx = cbegin(out);
     auto last_idx  = cend(out) - 1;
 
     // if there is a Higgs boson _not_ emitted off an incoming gluon,
     // extremal qqbar or unordered gluon outside the extremal partons
     // then it is not part of the FKL ladder
     // and does not contribute to the virtual corrections
     if((out.front().type == pid::Higgs && in.front().type != pid::gluon)
        || event.type() == event_type::unob
        || event.type() == event_type::qqbar_exb){
       q -= out[1].p;
       ++first_idx;
     }
     if((out.back().type == pid::Higgs && in.back().type != pid::gluon)
        || event.type() == event_type::unof
        || event.type() == event_type::qqbar_exf){
       --last_idx;
     }
 
     auto first_idx_qqbar = last_idx;
     auto last_idx_qqbar  = last_idx;
 
     //if central qqbar event, virtual correction do not occur between q-qbar.
     if(event.type() == event_type::qqbar_mid){
       const auto backquark = std::find_if(
         begin(out) + 1, end(out) - 1 ,
         [](Particle const & s){ return (s.type != pid::gluon && is_parton(s.type)); }
       );
       assert(backquark!=end(out)-1 && (backquark+1)->type!=pid::gluon);
       last_idx = backquark;
       first_idx_qqbar = last_idx+1;
     }
 
     double exponent = virtual_corrections_no_interference(first_idx, last_idx, q, mur);
 
     if(last_idx != first_idx_qqbar) {
       q -= (last_idx+1)->p;
       exponent += virtual_corrections_no_interference(first_idx_qqbar, last_idx_qqbar, q, mur);
     }
 
     assert(
         nearby(q, -1*pb, norm)
         || (out.back().type == pid::Higgs && in.back().type != pid::gluon)
         || event.type() == event_type::unof
         || event.type() == event_type::qqbar_exf
     );
 
     if (param_.nlo.enabled){
       const auto partons = filter_partons(event.outgoing());
       double nlo_virtual = 1.;
       // Only apply virtual corrections to a nlo order event.
       if(partons.size() == param_.nlo.nj) nlo_virtual += exponent;
       return {nlo_virtual};
     }
 
     return {std::exp(exponent)};
   }
 
 namespace {
 
   //! Lipatov vertex for partons emitted into extremal jets
   CLHEP::HepLorentzVector CLipatov(
       CLHEP::HepLorentzVector const & qav, CLHEP::HepLorentzVector const & qbv,
       CLHEP::HepLorentzVector const & p1, CLHEP::HepLorentzVector const & p2
   ) {
     const CLHEP::HepLorentzVector p5 = qav-qbv;
     const CLHEP::HepLorentzVector CL = -(qav+qbv)
       + p1*(qav.m2()/p5.dot(p1) + 2.*p5.dot(p2)/p1.dot(p2))
       - p2*(qbv.m2()/p5.dot(p2) + 2.*p5.dot(p1)/p1.dot(p2));
     return CL;
   }
 
   double C2Lipatov(
       CLHEP::HepLorentzVector const & qav,
       CLHEP::HepLorentzVector const & qbv,
       CLHEP::HepLorentzVector const & p1,
       CLHEP::HepLorentzVector const & p2
   ){
     const CLHEP::HepLorentzVector CL = CLipatov(qav, qbv, p1, p2);
     return -CL.dot(CL);
   }
 
   //! Lipatov vertex with soft subtraction for partons emitted into extremal jets
   double C2Lipatovots(
       CLHEP::HepLorentzVector const & qav,
       CLHEP::HepLorentzVector const & qbv,
       CLHEP::HepLorentzVector const & p1,
       CLHEP::HepLorentzVector const & p2,
       const double lambda
   ) {
     const double Cls=(C2Lipatov(qav, qbv, p1, p2)/(qav.m2()*qbv.m2()));
 
     const double kperp=(qav-qbv).perp();
     if (kperp>lambda)
       return Cls;
 
     return Cls-4./(kperp*kperp);
   }
 
   double C2Lipatov_Mix(
       CLHEP::HepLorentzVector const & qav_t, CLHEP::HepLorentzVector const & qbv_t,
       CLHEP::HepLorentzVector const & qav_b, CLHEP::HepLorentzVector const & qbv_b,
       CLHEP::HepLorentzVector const & p1, CLHEP::HepLorentzVector const & p2
   ) {
     const CLHEP::HepLorentzVector CL_t = CLipatov(qav_t, qbv_t, p1, p2);
     const CLHEP::HepLorentzVector CL_b = CLipatov(qav_b, qbv_b, p1, p2);
     return -CL_t.dot(CL_b);
   }
 
   double C2Lipatovots_Mix(
       CLHEP::HepLorentzVector const & qav_t, CLHEP::HepLorentzVector const & qbv_t,
       CLHEP::HepLorentzVector const & qav_b, CLHEP::HepLorentzVector const & qbv_b,
       CLHEP::HepLorentzVector const & p1, CLHEP::HepLorentzVector const & p2,
       const double lambda
   ) {
     const double Cls = C2Lipatov_Mix(qav_t, qbv_t, qav_b, qbv_b, p1, p2)
                        / sqrt(qav_t.m2() * qbv_t.m2() * qav_b.m2() * qbv_b.m2());
     const double kperp = (qav_t - qbv_t).perp();
     if (kperp > lambda){
       return Cls;
     }
     return Cls - 4.0 / (kperp * kperp);
 
   }
 
   CLHEP::HepLorentzVector CLipatov(
       CLHEP::HepLorentzVector const & qav, CLHEP::HepLorentzVector const & qbv,
       CLHEP::HepLorentzVector const & pim, CLHEP::HepLorentzVector const & pip,
       CLHEP::HepLorentzVector const & pom, CLHEP::HepLorentzVector const & pop
   ){
     const CLHEP::HepLorentzVector p5 = qav-qbv;
     const CLHEP::HepLorentzVector CL = -(qav+qbv)
       + qav.m2()*(1./p5.dot(pip)*pip + 1./p5.dot(pop)*pop)/2.
       - qbv.m2()*(1./p5.dot(pim)*pim + 1./p5.dot(pom)*pom)/2.
       + ( pip*(p5.dot(pim)/pip.dot(pim) + p5.dot(pom)/pip.dot(pom))
           + pop*(p5.dot(pim)/pop.dot(pim) + p5.dot(pom)/pop.dot(pom))
           - pim*(p5.dot(pip)/pip.dot(pim) + p5.dot(pop)/pop.dot(pim))
           - pom*(p5.dot(pip)/pip.dot(pom) + p5.dot(pop)/pop.dot(pom)) )/2.;
     return CL;
   }
 
   //! Lipatov vertex
   double C2Lipatov( // B
       CLHEP::HepLorentzVector const & qav,
       CLHEP::HepLorentzVector const & qbv,
       CLHEP::HepLorentzVector const & pim,
       CLHEP::HepLorentzVector const & pip,
       CLHEP::HepLorentzVector const & pom,
       CLHEP::HepLorentzVector const & pop
   ){
     const CLHEP::HepLorentzVector CL = CLipatov(qav, qbv, pim, pip, pom, pop);
     return -CL.dot(CL);
   }
 
   //! Lipatov vertex with soft subtraction
   double C2Lipatovots(
       CLHEP::HepLorentzVector const & qav,
       CLHEP::HepLorentzVector const & qbv,
       CLHEP::HepLorentzVector const & pa,
       CLHEP::HepLorentzVector const & pb,
       CLHEP::HepLorentzVector const & p1,
       CLHEP::HepLorentzVector const & p2,
       const double lambda
   ) {
     const double Cls=(C2Lipatov(qav, qbv, pa, pb, p1, p2)/(qav.m2()*qbv.m2()));
 
     const double kperp=(qav-qbv).perp();
     if (kperp>lambda)
       return Cls;
     return Cls-4./(kperp*kperp);
   }
 
   double C2Lipatov_Mix(
       CLHEP::HepLorentzVector const & qav_t, CLHEP::HepLorentzVector const & qbv_t,
       CLHEP::HepLorentzVector const & qav_b, CLHEP::HepLorentzVector const & qbv_b,
       CLHEP::HepLorentzVector const & pim, CLHEP::HepLorentzVector const & pip,
       CLHEP::HepLorentzVector const & pom, CLHEP::HepLorentzVector const & pop
   ) {
     const CLHEP::HepLorentzVector CL_t = CLipatov(qav_t, qbv_t, pim, pip, pom, pop);
     const CLHEP::HepLorentzVector CL_b = CLipatov(qav_b, qbv_b, pim, pip, pom, pop);
     return -CL_t.dot(CL_b);
   }
 
   double C2Lipatovots_Mix(
       CLHEP::HepLorentzVector const & qav_t, CLHEP::HepLorentzVector const & qbv_t,
       CLHEP::HepLorentzVector const & qav_b, CLHEP::HepLorentzVector const & qbv_b,
       CLHEP::HepLorentzVector const & pa, CLHEP::HepLorentzVector const & pb,
       CLHEP::HepLorentzVector const & p1, CLHEP::HepLorentzVector const & p2,
       const double lambda
   ) {
     const double Cls = C2Lipatov_Mix(qav_t, qbv_t, qav_b, qbv_b, pa, pb, p1, p2)
                        / sqrt(qav_t.m2() * qbv_t.m2() * qav_b.m2() * qbv_b.m2());
     const double kperp = (qav_t - qbv_t).perp();
     if (kperp > lambda) {
       return Cls;
     }
     return Cls - 4.0 / (kperp * kperp);
 
   }
 
   /** Matrix element squared for tree-level current-current scattering
    *  @param aptype          Particle a PDG ID
    *  @param bptype          Particle b PDG ID
    *  @param pg              Unordered gluon momentum
    *  @param pn              Particle n Momentum
    *  @param pb              Particle b Momentum
    *  @param p1              Particle 1 Momentum
    *  @param pa              Particle a Momentum
    *  @returns               ME Squared for Tree-Level Current-Current Scattering
    *
    *  @note The unof contribution can be calculated by reversing the argument ordering.
    */
   double ME_uno_current(
       [[maybe_unused]] ParticleID aptype,
       ParticleID bptype,
       CLHEP::HepLorentzVector const & pg,
       CLHEP::HepLorentzVector const & pn,
       CLHEP::HepLorentzVector const & pb,
       CLHEP::HepLorentzVector const & p1,
       CLHEP::HepLorentzVector const & pa
   ){
     assert(aptype!=pid::gluon); // aptype cannot be gluon
 
     const double t1 = (pa - p1 - pg).m2();
     const double t2 = (pb - pn).m2();
 
     return K_q * K(bptype, pn, pb)*currents::ME_unob_qq(pg, p1, pa, pn, pb) / (t1 * t2);
   }
 
   /** Matrix element squared for tree-level current-current scattering
    *  @param bptype   Particle b PDG ID
    *  @param pgin     Incoming gluon momentum
    *  @param p1       More backward (anti-)quark from splitting Momentum
    *  @param p2       Less backward (anti-)quark from splitting Momentum
    *  @param pn       Particle n Momentum
    *  @param pb       Particle b Momentum
    *  @returns        ME Squared for Tree-Level Current-Current Scattering
    *
    *  @note The forward qqbar contribution can be calculated by reversing the
    *        argument ordering.
    */
   double ME_qqbar_current(
       ParticleID bptype,
       CLHEP::HepLorentzVector const & pgin,
       CLHEP::HepLorentzVector const & p1,
       CLHEP::HepLorentzVector const & p2,
       CLHEP::HepLorentzVector const & pn,
       CLHEP::HepLorentzVector const & pb
   ){
     const double t1 = (pgin - p1 - p2).m2();
     const double t2 = (pn - pb).m2();
 
     return K_q * K(bptype, pn, pb)*currents::ME_qqbar_qg(pgin, pb, p1, p2, pn) / (t1 * t2);
   }
 
   /*  \brief Matrix element squared for central qqbar tree-level current-current
    *         scattering
    *
    *  @param aptype          Particle a PDG ID
    *  @param bptype          Particle b PDG ID
    *  @param nabove          Number of gluons emitted before central qqbarpair
    *  @param nbelow          Number of gluons emitted after central qqbarpair
    *  @param pa              Initial state a Momentum
    *  @param pb              Initial state b Momentum
    *  @param partons         Vector of all outgoing partons
    *  @param qbar_first      Ordering of the qqbar pair (true: qbar-q, false: q-qbar)
    *  @returns               ME Squared for qqbar_mid Tree-Level Current-Current Scattering
    */
   double ME_qqbar_mid_current(
       ParticleID aptype, ParticleID bptype, int nabove,
       CLHEP::HepLorentzVector const & pa,
       CLHEP::HepLorentzVector const & pb,
       std::vector<CLHEP::HepLorentzVector> const & partons,
       bool const qbar_first
   ){
     using namespace currents;
 
     CLHEP::HepLorentzVector const & p1 = partons.front();
     CLHEP::HepLorentzVector const & pn = partons.back();
 
     const double t1 = (p1 - pa).m2();
     const double t2 = (pb - pn).m2();
 
     return K(aptype, p1, pa)
       *K(bptype, pn, pb)
       *ME_Cenqqbar_qq(
         pa, pb, partons,
         qbar_first, nabove
       ) / (t1 * t2 * (4.*(N_C*N_C - 1)));
   }
 
 
   /** Matrix element squared for tree-level current-current scattering
    *  @param aptype          Particle a PDG ID
    *  @param bptype          Particle b PDG ID
    *  @param pn              Particle n Momentum
    *  @param pb              Particle b Momentum
    *  @param p1              Particle 1 Momentum
    *  @param pa              Particle a Momentum
    *  @returns               ME Squared for Tree-Level Current-Current Scattering
    */
   double ME_current(
       ParticleID aptype, ParticleID bptype,
       CLHEP::HepLorentzVector const & pn,
       CLHEP::HepLorentzVector const & pb,
       CLHEP::HepLorentzVector const & p1,
       CLHEP::HepLorentzVector const & pa
   ){
     const double t1 = (p1 - pa).m2();
     const double t2 = (pb - pn).m2();
 
     return K(aptype, p1, pa)
       * K(bptype, pn, pb)
       * currents::ME_qq(p1, pa, pn, pb)/(t1 * t2);
   }
 
   /** Matrix element squared for tree-level current-current scattering With W+Jets
    *  @param aptype          Particle a PDG ID
    *  @param bptype          Particle b PDG ID
    *  @param pn              Particle n Momentum
    *  @param pb              Particle b Momentum
    *  @param p1              Particle 1 Momentum
    *  @param pa              Particle a Momentum
    *  @param wc              Boolean. True->W Emitted from b. Else; emitted from leg a
    *  @returns               ME Squared for Tree-Level Current-Current Scattering
    */
   double ME_W_current(
       ParticleID aptype, ParticleID bptype,
       CLHEP::HepLorentzVector const & pn,
       CLHEP::HepLorentzVector const & pb,
       CLHEP::HepLorentzVector const & p1,
       CLHEP::HepLorentzVector const & pa,
       CLHEP::HepLorentzVector const & plbar,
       CLHEP::HepLorentzVector const & pl,
       bool const wc, ParticleProperties const & Wprop
   ){
     using namespace currents;
     assert(!(aptype==pid::gluon && bptype==pid::gluon));
 
     if(aptype == pid::gluon || wc) {
       // swap currents to ensure that the W is emitted off the first one
       return ME_W_current(bptype, aptype, p1, pa, pn, pb, plbar, pl, false, Wprop);
     }
 
     // we assume that the W is emitted off a quark line
     // if this is not the case, we have to apply CP conjugation,
     // which is equivalent to swapping lepton and antilepton momenta
     const double current_contr = is_quark(aptype)?
       ME_W_qQ(p1,plbar,pl,pa,pn,pb,Wprop):
       ME_W_qQ(p1,pl,plbar,pa,pn,pb,Wprop);
 
     const double t1 = (pa - p1 - pl - plbar).m2();
     const double tn = (pn - pb).m2();
 
     return K(aptype, p1, pa)
       * K(bptype, pn, pb)
       * current_contr/(4.*(N_C*N_C - 1) * t1 * tn);
   }
 
   /** Matrix element squared for backwards uno tree-level current-current
    *  scattering With W+Jets
    *
    *  @param aptype          Particle a PDG ID
    *  @param bptype          Particle b PDG ID
    *  @param pn              Particle n Momentum
    *  @param pb              Particle b Momentum
    *  @param p1              Particle 1 Momentum
    *  @param pa              Particle a Momentum
    *  @param pg              Unordered gluon momentum
    *  @param wc              Boolean. True->W Emitted from b. Else; emitted from leg a
    *  @returns               ME Squared for unob Tree-Level Current-Current Scattering
    *
    *  @note The unof contribution can be calculated by reversing the argument ordering.
    */
   double ME_W_uno_current(
       ParticleID aptype, ParticleID bptype,
       CLHEP::HepLorentzVector const & pn,
       CLHEP::HepLorentzVector const & pb,
       CLHEP::HepLorentzVector const & p1,
       CLHEP::HepLorentzVector const & pa,
       CLHEP::HepLorentzVector const & pg,
       CLHEP::HepLorentzVector plbar,
       CLHEP::HepLorentzVector pl,
       bool const wc, ParticleProperties const & Wprop
   ){
     using namespace currents;
     assert(bptype != pid::gluon || aptype != pid::gluon);
 
     if(aptype == pid::gluon || wc) {
       // emission off pb -- pn line
       // we assume that the W is emitted off a quark line
       // if this is not the case, we have to apply CP conjugation,
       // which is equivalent to swapping lepton and antilepton momenta
       if(is_antiquark(bptype)) std::swap(plbar, pl);
       const double t1 = (pa - p1 - pg).m2();
       const double tn = (pb - pn - plbar - pl).m2();
 
       return K_q*K_q*ME_W_unob_qQ(p1,pa,pn,pb,pg,plbar,pl,Wprop)/(4.*(N_C*N_C - 1) * t1 * tn);
     }
 
     // emission off pa -- p1 line
     if(is_antiquark(aptype)) std::swap(plbar, pl);
     const double t1 = (pa - p1 - pg - plbar - pl).m2();
     const double tn = (pb - pn).m2();
     return K(bptype, pn, pb)/C_F*ME_Wuno_qQ(p1,pa,pn,pb,pg,plbar,pl,Wprop)/(t1 * tn);
   }
 
   /** \brief Matrix element squared for backward qqbar tree-level current-current
    *         scattering With W+Jets
    *
    *  @param bptype          Particle b PDG ID
    *  @param pa              Initial state a Momentum
    *  @param pb              Initial state b Momentum
    *  @param pq              Final state q Momentum
    *  @param pqbar           Final state qbar Momentum
    *  @param pn              Final state n Momentum
    *  @param plbar           Final state anti-lepton momentum
    *  @param pl              Final state lepton momentum
    *  @param wc              Boolean. True->W Emitted from b. Else; emitted from leg a
    *  @returns               ME Squared for qqbarb Tree-Level Current-Current Scattering
    *
    *  @note calculate forwards qqbar contribution by reversing argument ordering.
    */
   double ME_W_qqbar_current(
       ParticleID bptype,
       CLHEP::HepLorentzVector const & pa,
       CLHEP::HepLorentzVector const & pb,
       CLHEP::HepLorentzVector const & pq,
       CLHEP::HepLorentzVector const & pqbar,
       CLHEP::HepLorentzVector const & pn,
       CLHEP::HepLorentzVector const & plbar,
       CLHEP::HepLorentzVector const & pl,
       bool const wc,
       ParticleProperties const & Wprop
   ){
     using namespace currents;
     if(is_anyquark(bptype) && wc) {
       // W Must be emitted from forwards leg.
       const double t1 = (pa - pq - pqbar).m2();
       const double tn = (pb - pn - pl - plbar).m2();
 
       return K_q * K_q * ME_W_Exqqbar_QQq(
         pb, pa, pn, pq, pqbar, plbar, pl, is_antiquark(bptype), Wprop
       ) / (4.*(N_C*N_C - 1) * t1 * tn);
     }
 
     const double t1 = (pa - pl - plbar - pq - pqbar).m2();
     const double tn = (pb - pn).m2();
 
     return K(bptype, pn, pb)/C_F
       * ME_WExqqbar_qqbarQ(pa, pqbar, plbar, pl, pq, pn, pb, Wprop) / (t1 * tn);
   }
 
   /*  \brief Matrix element squared for central qqbar tree-level current-current
    *         scattering With W+Jets
    *
    *  @param aptype          Particle a PDG ID
    *  @param bptype          Particle b PDG ID
    *  @param nabove          Number of gluons emitted before central qqbarpair
    *  @param nbelow          Number of gluons emitted after central qqbarpair
    *  @param pa              Initial state a Momentum
    *  @param pb              Initial state b Momentum\
    *  @param partons         Vector of all outgoing partons
    *  @param plbar           Final state anti-lepton momentum
    *  @param pl              Final state lepton momentum
    *  @param qbar_first      Ordering of the qqbar pair (true: qbar-q, false: q-qbar)
    *  @param wqq             Boolean. True siginfies W boson is emitted from Central qqbar
    *  @param wc              Boolean. wc=true signifies w boson emitted from leg b; if wqq=false.
    *  @returns               ME Squared for qqbar_mid Tree-Level Current-Current Scattering
    */
   double ME_W_qqbar_mid_current(
       ParticleID aptype, ParticleID bptype,
       int nabove, int nbelow,
       CLHEP::HepLorentzVector const & pa,
       CLHEP::HepLorentzVector const & pb,
       std::vector<CLHEP::HepLorentzVector> const & partons,
       CLHEP::HepLorentzVector const & plbar,
       CLHEP::HepLorentzVector const & pl,
       bool const qbar_first, bool const wqq, bool const wc,
       ParticleProperties const & Wprop
   ){
     using namespace currents;
 
     const double wt = K(aptype, partons.front(), pa) * K(bptype, partons.back(), pb) / (4.*(N_C*N_C - 1));
 
     if(wqq)
       return wt*ME_WCenqqbar_qq(pa, pb, pl, plbar, partons,
                                 is_antiquark(aptype),is_antiquark(bptype),
                                 qbar_first, nabove, Wprop);
     return wt*ME_W_Cenqqbar_qq(pa, pb, pl, plbar, partons,
                                is_antiquark(aptype), is_antiquark(bptype),
                                qbar_first, nabove, nbelow, wc, Wprop);
   }
 
   /** Matrix element squared for tree-level current-current scattering With Z+Jets
    *  @param aptype          Particle a PDG ID
    *  @param bptype          Particle b PDG ID
    *  @param pn              Particle n Momentum
    *  @param pb              Particle b Momentum
    *  @param p1              Particle 1 Momentum
    *  @param pa              Particle a Momentum
    *  @param plbar           Final state positron momentum
    *  @param pl              Final state electron momentum
    *  @param Zprop           Z properties
    *  @param stw2            Value of sin(theta_w)^2
    *  @param ctw             Value of cos(theta_w)
    *  @returns               ME Squared for Tree-Level Current-Current Scattering
    */
   std::vector<double> ME_Z_current(
       const ParticleID aptype, const ParticleID bptype,
       CLHEP::HepLorentzVector const & pn,
       CLHEP::HepLorentzVector const & pb,
       CLHEP::HepLorentzVector const & p1,
       CLHEP::HepLorentzVector const & pa,
       const ParticleID ltype,
       CLHEP::HepLorentzVector const & plbar,
       CLHEP::HepLorentzVector const & pl,
       ParticleProperties const & Zprop,
       const double stw2, const double ctw
   ){
     using namespace currents;
 
     const auto pZ = pl + plbar;
 
     const double pref = K(aptype, p1, pa) * K(bptype, pn, pb)/(4.*(N_C*N_C-1));
 
     // we know they are not both gluons
     assert(!is_gluon(aptype) || !is_gluon(bptype));
 
     if(is_anyquark(aptype) && is_gluon(bptype)){
       // This is a qg event
       const double t1 = (pa-p1-pZ).m2();
       const double tn = (pb-pn   ).m2();
       return { pref*ME_Z_qg(pa,pb,p1,pn,plbar,pl,aptype,bptype,ltype,Zprop,stw2,ctw)/(t1 * tn) };
     }
 
     if(is_gluon(aptype) && is_anyquark(bptype)){
       // This is a gq event
       const double t1 = (pa-p1   ).m2();
       const double tn = (pb-pn-pZ).m2();
       return { pref*ME_Z_qg(pb,pa,pn,p1,plbar,pl,bptype,aptype,ltype,Zprop,stw2,ctw)/(t1 * tn) };
     }
 
     // This is a qq event
     assert(is_anyquark(aptype) && is_anyquark(bptype));
     const double t1_top = (pa-p1-pZ).m2();
     const double t2_top = (pb-pn   ).m2();
 
     const double t1_bot = (pa-p1   ).m2();
     const double t2_bot = (pb-pn-pZ).m2();
     std::vector<double> res = ME_Z_qQ(pa,pb,p1,pn,plbar,pl,aptype,bptype,ltype,Zprop,stw2,ctw);
     assert(res.size() == 3);
 
     res[0] *= pref/(t1_top * t2_top);
     res[1] *= pref/(t1_bot * t2_bot);
     res[2] *= pref/sqrt(t1_top * t2_top * t1_bot * t2_bot);
 
     return res;
   }
 
   /** Matrix element squared for backwards uno tree-level current-current
    *  scattering With Z+Jets
    *
    *  @param aptype          Particle a PDG ID
    *  @param bptype          Particle b PDG ID
    *  @param pn              Particle n Momentum
    *  @param pb              Particle b Momentum
    *  @param p1              Particle 1 Momentum
    *  @param pa              Particle a Momentum
    *  @param pg              Unordered gluon momentum
    *  @param plbar           Final state positron momentum
    *  @param pl              Final state electron momentum
    *  @param Zprop           Z properties
    *  @param stw2            Value of sin(theta_w)^2
    *  @param ctw             Value of cos(theta_w)
    *  @returns               ME Squared for unob Tree-Level Current-Current Scattering
    *
    *  @note The unof contribution can be calculated by reversing the argument ordering.
    */
 
   std::vector<double> ME_Z_uno_current(
       const ParticleID aptype, const ParticleID bptype,
       CLHEP::HepLorentzVector const & pn,
       CLHEP::HepLorentzVector const & pb,
       CLHEP::HepLorentzVector const & p1,
       CLHEP::HepLorentzVector const & pa,
       CLHEP::HepLorentzVector const & pg,
       const ParticleID ltype,
       CLHEP::HepLorentzVector const & plbar,
       CLHEP::HepLorentzVector const & pl,
       ParticleProperties const & Zprop,
       const double stw2, const double ctw
   ){
     using namespace currents;
 
     const auto pZ = pl + plbar;
 
     const double pref = K(aptype, p1, pa)/C_F * K(bptype, pn, pb)/C_F;
 
     // we only evaluate unordered backward -> first incoming particle must be a quark
     assert(is_anyquark(aptype));
 
     const double t1_top = (pa-pg-p1-pZ).m2();
     const double t2_top = (pb-pn      ).m2();
 
     if (is_gluon(bptype)) {
       // This is a qg event -> Z emission from top leg
       return { pref*ME_Zuno_qg(pa,pb,pg,p1,pn,plbar,pl,aptype,bptype,ltype,Zprop,stw2,ctw)/(t1_top * t2_top) };
     }
 
     // This is a qq event
     assert(is_anyquark(bptype));
 
     const double t1_bot = (pa-pg-p1).m2();
     const double t2_bot = (pb-pn-pZ).m2();
 
     std::vector<double> res = ME_Zuno_qQ(pa,pb,pg,p1,pn,plbar,pl,aptype,bptype,ltype,Zprop,stw2,ctw);
     assert(res.size() == 3);
 
     res[0] *= pref/(t1_top * t2_top);
     res[1] *= pref/(t1_bot * t2_bot);
     res[2] *= pref/sqrt(t1_top * t2_top * t1_bot * t2_bot);
 
     return res;
   }
 
   /** Matrix element squared for backwards extremal qqbar tree-level current-current
    *  scattering With Z+Jets
    *
    *  @param qptype          PDG ID of final state quark in qqbar pair
    *  @param bptype          Incoming particle b PDG ID
    *  @param pa              Incoming particle a momentum
    *  @param pb              Incoming particle b momentum
    *  @param pq              Final state quark momentum
    *  @param pqbar           Final state anti-quark momentum
    *  @param pn              Final state particle n momentum
    *  @param plbar           Final state positron momentum
    *  @param pl              Final state electron momentum
    *  @param Zprop           Z properties
    *  @param stw2            Value of sin(theta_w)^2
    *  @param ctw             Value of cos(theta_w)
    *  @returns               ME Squared for qqbar_exb Tree-Level Current-Current Scattering
    *
    *  @note The qqbar_exf contribution can be calculated by reversing the argument ordering.
    */
   std::vector<double> ME_Z_exqqbar_current(
       const ParticleID qptype, const ParticleID bptype,
       CLHEP::HepLorentzVector const & pa,
       CLHEP::HepLorentzVector const & pb,
       CLHEP::HepLorentzVector const & pq,
       CLHEP::HepLorentzVector const & pqbar,
       CLHEP::HepLorentzVector const & pn,
       const ParticleID ltype,
       CLHEP::HepLorentzVector const & plbar,
       CLHEP::HepLorentzVector const & pl,
       ParticleProperties const & Zprop,
       const double stw2, const double ctw
   ){
     using namespace currents;
 
     const auto pZ = pl + plbar;
 
     const double t1_top = (pa-pq-pqbar-pZ).m2();
     const double t2_top = (pb-pn).m2();
 
     if (is_gluon(bptype)) {
       // This is a gg event -> Z emission from top leg
       return { K(bptype, pn, pb)/C_F
                * ME_ZExqqbar_gg(pa,pb,pq,pqbar,pn,plbar,pl,qptype,ltype,Zprop,stw2,ctw)
                / (t1_top * t2_top) };
     }
 
     // This is a gq event
     assert(is_anyquark(bptype));
 
     const double t1_bot = (pa-pq-pqbar).m2();
     const double t2_bot = (pb-pn-pZ).m2();
 
     std::vector<double> res = ME_ZExqqbar_gq(pa,pb,pq,pqbar,pn,plbar,pl,qptype,bptype,ltype,Zprop,stw2,ctw);
     assert(res.size() == 3);
 
     res[0] /= (t1_top * t2_top);
     res[1] /= (t1_bot * t2_bot);
     res[2] /= sqrt(t1_top * t2_top * t1_bot * t2_bot);
 
     return res;
   }
 
   /** Matrix element squared for central qqbar tree-level current-current
    *  scattering With Z+Jets
    *
    *  @param aptype          Incoming particle a PDG ID
    *  @param bptype          Incoming particle b PDG ID
    *  @param qptype          PDG ID of final state quark in qqbar pair
    *  @param qbar_first      Ordering of the qqbar pair (true: qbar-q, false: q-qbar)
    *  @param nabove          Number of gluons emitted before central qqbarpair
    *  @param pa              Incoming particle a momentum
    *  @param pb              Incoming particle b momentum
    *  @param partons         Vector of all outgoing partons
    *  @param plbar           Final state positron momentum
    *  @param pl              Final state electron momentum
    *  @param Zprop           Z properties
    *  @param stw2            Value of sin(theta_w)^2
    *  @param ctw             Value of cos(theta_w)
    *  @returns               ME Squared for central qqbar Tree-Level Current-Current Scattering
    */
   std::vector<double> ME_Z_qqbar_mid_current(
       const ParticleID aptype, const ParticleID bptype,
       const ParticleID qptype,
       const bool qbar_first, const int nabove,
       CLHEP::HepLorentzVector const & pa,
       CLHEP::HepLorentzVector const & pb,
       std::vector<CLHEP::HepLorentzVector> const & partons,
       const ParticleID ltype,
       CLHEP::HepLorentzVector const & plbar,
       CLHEP::HepLorentzVector const & pl,
       ParticleProperties const & Zprop,
       const double stw2, const double ctw
   ){
     using namespace currents;
 
     std::vector<double> res;
     if(is_gluon(aptype)) {
       if(is_gluon(bptype)) {
         // gg event
         res = { ME_ZCenqqbar_gg(pa,pb,plbar,pl,partons,qbar_first,nabove,qptype,ltype,Zprop,stw2,ctw) };
       } else {
         // gq event
         res = ME_ZCenqqbar_gq(pa,pb,plbar,pl,partons,qbar_first,nabove,bptype,qptype,ltype,Zprop,stw2,ctw);
       }
     } else {
       assert(is_anyquark(bptype));
       // qq event
       res = ME_ZCenqqbar_qq(pa,pb,plbar,pl,partons,qbar_first,nabove,aptype,bptype,qptype,ltype,Zprop,stw2,ctw);
     }
 
     const double wt = K(aptype, partons.front(), pa) * K(bptype, partons.back(), pb) / (4.*(N_C*N_C - 1));
 
     for(double & me: res) me *= wt;
 
     return res;
   }
 
   /** \brief Matrix element squared for tree-level current-current scattering with Higgs
    *  @param aptype          Particle a PDG ID
    *  @param bptype          Particle b PDG ID
    *  @param pn              Particle n Momentum
    *  @param pb              Particle b Momentum
    *  @param p1              Particle 1 Momentum
    *  @param pa              Particle a Momentum
    *  @param qH              t-channel momentum before Higgs
    *  @param qHp1            t-channel momentum after Higgs
    *  @returns               ME Squared for Tree-Level Current-Current Scattering with Higgs
    */
   double ME_Higgs_current(
       ParticleID aptype, ParticleID bptype,
       CLHEP::HepLorentzVector const & pn,
       CLHEP::HepLorentzVector const & pb,
       CLHEP::HepLorentzVector const & p1,
       CLHEP::HepLorentzVector const & pa,
       CLHEP::HepLorentzVector const & qH,  // t-channel momentum before Higgs
       CLHEP::HepLorentzVector const & qHp1, // t-channel momentum after Higgs
       double mt, bool include_bottom, double mb, double vev
   ){
     const double t1 = (pa - p1).m2();
     const double tn = (pb - pn).m2();
 
     return
       K(aptype, p1, pa)
       *K(bptype, pn, pb)
       *currents::ME_H_qQ(
         pn,pb,p1,pa,-qHp1,-qH,mt,include_bottom,mb,vev
       ) / (t1 * tn * qH.m2() * qHp1.m2());
   }
 
   /** \brief Current matrix element squared with Higgs and unordered backward emission
    *  @param aptype          Particle A PDG ID
    *  @param bptype          Particle B PDG ID
    *  @param pn              Particle n Momentum
    *  @param pb              Particle b Momentum
    *  @param pg              Unordered back Particle Momentum
    *  @param p1              Particle 1 Momentum
    *  @param pa              Particle a Momentum
    *  @param qH              t-channel momentum before Higgs
    *  @param qHp1            t-channel momentum after Higgs
    *  @returns               ME Squared with Higgs and unordered backward emission
    *
    *  @note This function assumes unordered gluon backwards from pa-p1 current.
    *        For unof, reverse call order
    */
   double ME_Higgs_current_uno(
       ParticleID aptype, ParticleID bptype,
       CLHEP::HepLorentzVector const & pg,
       CLHEP::HepLorentzVector const & pn,
       CLHEP::HepLorentzVector const & pb,
       CLHEP::HepLorentzVector const & p1,
       CLHEP::HepLorentzVector const & pa,
       CLHEP::HepLorentzVector const & qH,  // t-channel momentum before Higgs
       CLHEP::HepLorentzVector const & qHp1, // t-channel momentum after Higgs
       double mt, bool include_bottom, double mb, double vev
   ){
     const double t1 = (pa - p1 - pg).m2();
     const double tn = (pn - pb).m2();
 
     return
       K(aptype, p1, pa)
       *K(bptype, pn, pb)
       *currents::ME_H_unob_qQ(
         pg,p1,pa,pn,pb,-qH,-qHp1,mt,include_bottom,mb,vev
       ) / (t1 * qH.m2() * qHp1.m2() * tn);
   }
 
   /** Matrix element squared for tree-level scattering with WW+Jets
    *  @param aptype          Particle a PDG ID
    *  @param bptype          Particle b PDG ID
    *  @param pn              Particle n Momentum
    *  @param pb              Particle b Momentum
    *  @param p1              Particle 1 Momentum
    *  @param pa              Particle a Momentum
    *  @param pl1bar          Particle l1bar Momentum
    *  @param pl1             Particle l1 Momentum
    *  @param pl2bar          Particle l2bar Momentum
    *  @param pl2             Particle l2 Momentum
    *  @returns               ME Squared for Tree-Level Current-Current Scattering
    */
   std::vector <double> ME_WW_current(
       ParticleID aptype, ParticleID bptype,
       CLHEP::HepLorentzVector const & pn,
       CLHEP::HepLorentzVector const & pb,
       CLHEP::HepLorentzVector const & p1,
       CLHEP::HepLorentzVector const & pa,
       CLHEP::HepLorentzVector const & pl1bar,
       CLHEP::HepLorentzVector const & pl1,
       CLHEP::HepLorentzVector const & pl2bar,
       CLHEP::HepLorentzVector const & pl2,
       ParticleProperties const & Wprop
   ){
     using namespace currents;
 
     if (aptype > 0 && bptype > 0)
       return ME_WW_qQ(p1, pl1bar, pl1, pa, pn, pl2bar, pl2, pb, Wprop);
     if (aptype < 0 && bptype > 0)
       return ME_WW_qbarQ(p1, pl1bar, pl1, pa, pn, pl2bar, pl2, pb, Wprop);
     if (aptype > 0 && bptype < 0)
       return ME_WW_qQbar(p1, pl1bar, pl1, pa, pn, pl2bar, pl2, pb, Wprop);
     if (aptype < 0 && bptype < 0)
       return ME_WW_qbarQbar(p1, pl1bar, pl1, pa, pn, pl2bar, pl2, pb, Wprop);
 
     throw std::logic_error("unreachable");
   }
 
   void validate(MatrixElementConfig const & config) {
 #ifndef HEJ_BUILD_WITH_QCDLOOP
     if(!config.Higgs_coupling.use_impact_factors) {
       throw std::invalid_argument{
         "Invalid Higgs coupling settings.\n"
         "HEJ without QCDloop support can only use impact factors.\n"
         "Set use_impact_factors to true or recompile HEJ.\n"
        };
     }
 #endif
     if(config.Higgs_coupling.use_impact_factors
       && config.Higgs_coupling.mt != std::numeric_limits<double>::infinity()) {
       throw std::invalid_argument{
         "Conflicting settings: "
           "impact factors may only be used in the infinite top mass limit"
       };
     }
   }
 } // namespace
 
   MatrixElement::MatrixElement(
       std::function<double (double)> alpha_s,
       MatrixElementConfig conf
   ):
     alpha_s_{std::move(alpha_s)},
     param_{std::move(conf)}
   {
     validate(param_);
   }
 
   std::vector<double> MatrixElement::tree_kin(
       Event const & ev
   ) const {
     if(!ev.valid_hej_state(param_.soft_pt_regulator)) return {0.};
 
     if(!ev.valid_incoming()){
       throw std::invalid_argument{
         "Invalid momentum for one or more incoming particles. "
         "Incoming momenta must have vanishing mass and transverse momentum."
       };
     }
 
     std::vector<Particle> bosons = filter_AWZH_bosons(ev.outgoing());
 
     if(bosons.empty()) {
       return {tree_kin_jets(ev)};
     }
 
     if(bosons.size() == 1) {
       switch(bosons[0].type){
       case pid::Higgs:
         return {tree_kin_Higgs(ev)};
       case pid::Wp:
       case pid::Wm:
         return {tree_kin_W(ev)};
+      case pid::Z:
       case pid::Z_photon_mix:
         return tree_kin_Z(ev);
       // TODO
       case pid::photon:
-      case pid::Z:
       default:
         throw not_implemented("Emission of boson of unsupported type");
       }
     }
 
     if(bosons.size() == 2) {
       if(bosons[0].type == pid::Wp && bosons[1].type == pid::Wp){
         return tree_kin_WW(ev);
       }
       else if(bosons[0].type == pid::Wm && bosons[1].type == pid::Wm){
         return tree_kin_WW(ev);
       }
 
       throw not_implemented("Emission of bosons of unsupported type");
     }
 
     throw not_implemented("Emission of >2 bosons is unsupported");
   }
 
   namespace {
     constexpr int EXTREMAL_JET_IDX = 1;
     constexpr int NO_EXTREMAL_JET_IDX = 0;
 
     bool treat_as_extremal(Particle const & parton){
       return parton.p.user_index() == EXTREMAL_JET_IDX;
     }
 
     template<class InputIterator>
     double FKL_ladder_weight(
         InputIterator begin_gluon, InputIterator end_gluon,
         CLHEP::HepLorentzVector const & q0,
         CLHEP::HepLorentzVector const & pa, CLHEP::HepLorentzVector const & pb,
         CLHEP::HepLorentzVector const & p1, CLHEP::HepLorentzVector const & pn,
         double lambda
     ){
       double wt = 1;
       auto qi = q0;
       for(auto gluon_it = begin_gluon; gluon_it != end_gluon; ++gluon_it){
         assert(gluon_it->type == pid::gluon);
         const auto g = to_HepLorentzVector(*gluon_it);
         const auto qip1 = qi - g;
 
         if(treat_as_extremal(*gluon_it)){
           wt *= C2Lipatovots(qip1, qi, pa, pb, lambda)*C_A;
         } else{
           wt *= C2Lipatovots(qip1, qi, pa, pb, p1, pn, lambda)*C_A;
         }
 
         qi = qip1;
       }
       return wt;
     }
 
     template<class InputIterator>
     std::vector <double> FKL_ladder_weight_mix(
         InputIterator begin_gluon, InputIterator end_gluon,
         CLHEP::HepLorentzVector const & q0_t, CLHEP::HepLorentzVector const & q0_b,
         CLHEP::HepLorentzVector const & pa, CLHEP::HepLorentzVector const & pb,
         CLHEP::HepLorentzVector const & p1, CLHEP::HepLorentzVector const & pn,
         const double lambda
     ){
       double wt_top = 1;
       double wt_bot = 1;
       double wt_mix = 1;
       auto qi_t = q0_t;
       auto qi_b = q0_b;
       for(auto gluon_it = begin_gluon; gluon_it != end_gluon; ++gluon_it){
         assert(gluon_it->type == pid::gluon);
         const auto g = to_HepLorentzVector(*gluon_it);
         const auto qip1_t = qi_t - g;
         const auto qip1_b = qi_b - g;
         if(treat_as_extremal(*gluon_it)){
           wt_top *= C2Lipatovots(qip1_t, qi_t, pa, pb, lambda)*C_A;
           wt_bot *= C2Lipatovots(qip1_b, qi_b, pa, pb, lambda)*C_A;
           wt_mix *= C2Lipatovots_Mix(qip1_t, qi_t, qip1_b, qi_b, pa, pb, lambda)*C_A;
         } else{
           wt_top *= C2Lipatovots(qip1_t, qi_t, pa, pb, p1, pn, lambda)*C_A;
           wt_bot *= C2Lipatovots(qip1_b, qi_b, pa, pb, p1, pn, lambda)*C_A;
           wt_mix *= C2Lipatovots_Mix(qip1_t, qi_t, qip1_b, qi_b, pa, pb, p1, pn, lambda)*C_A;
         }
         qi_t = qip1_t;
         qi_b = qip1_b;
       }
       return {wt_top, wt_bot, wt_mix};
     }
 
     std::vector<Particle> tag_extremal_jet_partons( Event const & ev ){
       auto out_partons = filter_partons(ev.outgoing());
       if(out_partons.size() == ev.jets().size()){
         // no additional emissions in extremal jets, don't need to tag anything
         for(auto & parton: out_partons){
           parton.p.set_user_index(NO_EXTREMAL_JET_IDX);
         }
         return out_partons;
       }
       auto const & jets = ev.jets();
       std::vector<fastjet::PseudoJet> extremal_jets;
       if(! is_backward_g_to_h(ev)) {
         auto most_backward = begin(jets);
         // skip jets caused by unordered emission or qqbar
         if(ev.type() == event_type::unob || ev.type() == event_type::qqbar_exb){
           assert(jets.size() >= 2);
           ++most_backward;
         }
         extremal_jets.emplace_back(*most_backward);
       }
       if(! is_forward_g_to_h(ev)) {
         auto most_forward = end(jets) - 1;
         if(ev.type() == event_type::unof || ev.type() == event_type::qqbar_exf){
           assert(jets.size() >= 2);
           --most_forward;
         }
         extremal_jets.emplace_back(*most_forward);
       }
       const auto extremal_jet_indices = ev.particle_jet_indices(
         extremal_jets
       );
       assert(extremal_jet_indices.size() == out_partons.size());
       for(std::size_t i = 0; i < out_partons.size(); ++i){
         assert(is_parton(out_partons[i]));
         const int idx = (extremal_jet_indices[i]>=0)?
           EXTREMAL_JET_IDX:
           NO_EXTREMAL_JET_IDX;
         out_partons[i].p.set_user_index(idx);
       }
       return out_partons;
     }
 
     double tree_kin_jets_qqbar_mid(
         ParticleID aptype, ParticleID bptype,
         CLHEP::HepLorentzVector const & pa, CLHEP::HepLorentzVector const & pb,
         std::vector<Particle> const & partons,
         double lambda
     ){
       const auto backmidquark = std::find_if(
           begin(partons)+1, end(partons)-1,
           [](Particle const & s){ return s.type != pid::gluon; }
       );
 
       assert(backmidquark!=end(partons)-1);
 
       const bool qbar_first = is_antiquark(backmidquark->type);
 
       const auto pq    = to_HepLorentzVector(*(backmidquark+(qbar_first?1:0)));
       const auto pqbar = to_HepLorentzVector(*(backmidquark+(qbar_first?0:1)));
 
       const auto p1 = to_HepLorentzVector(partons[0]);
       const auto pn = to_HepLorentzVector(partons[partons.size() - 1]);
 
       const auto begin_ladder_1 = cbegin(partons) + 1;
       const auto end_ladder_1   = (backmidquark);
       const auto begin_ladder_2 = (backmidquark+2);
       const auto end_ladder_2   = cend(partons) - 1;
 
       const int nabove = std::distance(begin_ladder_1, end_ladder_1);
 
       const auto q0 = pa - p1;
       // t-channel momentum after qqbar
       auto q3 = q0;
       for(auto parton_it = begin_ladder_1; parton_it != begin_ladder_2; ++parton_it){
         q3 -= to_HepLorentzVector(*parton_it);
       }
 
       std::vector<CLHEP::HepLorentzVector> partonsHLV;
       partonsHLV.reserve(partons.size());
       for(Particle const & parton: partons) {
         partonsHLV.push_back(to_HepLorentzVector(parton));
       }
 
       const double current_factor = ME_qqbar_mid_current(
           aptype, bptype, nabove, pa, pb,
           partonsHLV, qbar_first
       );
 
       const double ladder_factor = FKL_ladder_weight(
           begin_ladder_1, end_ladder_1,
           q0, pa, pb, p1, pn,
           lambda
       )*FKL_ladder_weight(
           begin_ladder_2, end_ladder_2,
           q3, pa, pb, p1, pn,
           lambda
         );
       return current_factor*ladder_factor;
     }
 
 
     template<class InIter, class partIter>
     double tree_kin_jets_qqbar(InIter begin_in, InIter end_in, partIter begin_part,
                                partIter end_part, double lambda){
       const auto pgin = to_HepLorentzVector(*begin_in);
       const auto pb   = to_HepLorentzVector(*(end_in-1));
       const auto p1   = to_HepLorentzVector(*begin_part);
       const auto p2   = to_HepLorentzVector(*(begin_part+1));
       const auto pn   = to_HepLorentzVector(*(end_part-1));
 
       assert((begin_in)->type==pid::gluon); // Incoming a must be gluon.
       const double current_factor = ME_qqbar_current(
         (end_in-1)->type, pgin, p1, p2, pn, pb
         )/(4.*(N_C*N_C - 1.));
       const double ladder_factor = FKL_ladder_weight(
           (begin_part+2), (end_part-1),
           pgin-p1-p2, pgin, pb, p1, pn, lambda
           );
 
       return current_factor*ladder_factor;
     }
 
     template<class InIter, class partIter>
     double tree_kin_jets_uno(InIter begin_in, InIter end_in, partIter begin_part,
                              partIter end_part, double lambda
     ){
 
       const auto pa = to_HepLorentzVector(*begin_in);
       const auto pb = to_HepLorentzVector(*(end_in-1));
 
       const auto pg = to_HepLorentzVector(*begin_part);
       const auto p1 = to_HepLorentzVector(*(begin_part+1));
       const auto pn = to_HepLorentzVector(*(end_part-1));
 
       const double current_factor = ME_uno_current(
         (begin_in)->type, (end_in-1)->type, pg, pn, pb, p1, pa
       )/(4.*(N_C*N_C - 1.));
       const double ladder_factor = FKL_ladder_weight(
           (begin_part+2), (end_part-1),
           pa-p1-pg, pa, pb, p1, pn, lambda
           );
 
       return current_factor*ladder_factor;
     }
   } // namespace
 
   double MatrixElement::tree_kin_jets(Event const & ev) const {
     auto const & incoming = ev.incoming();
     const auto partons = tag_extremal_jet_partons(ev);
 
     if (ev.type()==event_type::FKL){
       const auto pa = to_HepLorentzVector(incoming[0]);
       const auto pb = to_HepLorentzVector(incoming[1]);
 
       const auto p1 = to_HepLorentzVector(partons.front());
       const auto pn = to_HepLorentzVector(partons.back());
       return ME_current(
         incoming[0].type, incoming[1].type,
         pn, pb, p1, pa
         )/(4.*(N_C*N_C - 1.))*FKL_ladder_weight(
           begin(partons) + 1, end(partons) - 1,
           pa - p1, pa, pb, p1, pn,
           param_.regulator_lambda
         );
     }
     if (ev.type()==event_type::unordered_backward){
       return tree_kin_jets_uno(incoming.begin(), incoming.end(),
                                partons.begin(), partons.end(),
                                param_.regulator_lambda);
     }
     if (ev.type()==event_type::unordered_forward){
       return tree_kin_jets_uno(incoming.rbegin(), incoming.rend(),
                                partons.rbegin(), partons.rend(),
                                param_.regulator_lambda);
     }
     if (ev.type()==event_type::extremal_qqbar_backward){
       return tree_kin_jets_qqbar(incoming.begin(), incoming.end(),
                                  partons.begin(), partons.end(),
                                  param_.regulator_lambda);
     }
     if (ev.type()==event_type::extremal_qqbar_forward){
       return tree_kin_jets_qqbar(incoming.rbegin(), incoming.rend(),
                                  partons.rbegin(), partons.rend(),
                                  param_.regulator_lambda);
     }
     if (ev.type()==event_type::central_qqbar){
       return tree_kin_jets_qqbar_mid(incoming[0].type, incoming[1].type,
                                      to_HepLorentzVector(incoming[0]),
                                      to_HepLorentzVector(incoming[1]),
                                      partons, param_.regulator_lambda);
    }
     throw std::logic_error("Cannot reweight non-resummable processes in Pure Jets");
   }
 
   namespace {
     double tree_kin_W_FKL(
         ParticleID aptype, ParticleID bptype,
         CLHEP::HepLorentzVector const & pa, CLHEP::HepLorentzVector const & pb,
         std::vector<Particle> const & partons,
         CLHEP::HepLorentzVector const & plbar, CLHEP::HepLorentzVector const & pl,
         double lambda, ParticleProperties const & Wprop
     ){
       auto p1 = to_HepLorentzVector(partons[0]);
       auto pn = to_HepLorentzVector(partons[partons.size() - 1]);
 
       const auto begin_ladder = cbegin(partons) + 1;
       const auto end_ladder = cend(partons) - 1;
 
       bool wc = aptype==partons[0].type; //leg b emits w
       auto q0 = pa - p1;
       if(!wc)
         q0 -= pl + plbar;
 
       const double current_factor = ME_W_current(
           aptype, bptype, pn, pb,
           p1, pa, plbar, pl, wc, Wprop
       );
 
       const double ladder_factor = FKL_ladder_weight(
           begin_ladder, end_ladder,
           q0, pa, pb, p1, pn,
           lambda
       );
       return current_factor*ladder_factor;
     }
 
 
     template<class InIter, class partIter>
     double tree_kin_W_uno(InIter begin_in, partIter begin_part,
                           partIter end_part,
                           const CLHEP::HepLorentzVector & plbar,
                           const CLHEP::HepLorentzVector & pl,
                           double lambda, ParticleProperties const & Wprop
     ){
       const auto pa = to_HepLorentzVector(*begin_in);
       const auto pb = to_HepLorentzVector(*(begin_in+1));
 
       const auto pg = to_HepLorentzVector(*begin_part);
       const auto p1 = to_HepLorentzVector(*(begin_part+1));
       const auto pn = to_HepLorentzVector(*(end_part-1));
 
       bool wc = (begin_in)->type==(begin_part+1)->type; //leg b emits w
       auto q0 = pa - p1 - pg;
       if(!wc)
         q0 -= pl + plbar;
 
       const double current_factor = ME_W_uno_current(
           (begin_in)->type, (begin_in+1)->type, pn, pb,
           p1, pa, pg, plbar, pl, wc, Wprop
       );
 
       const double ladder_factor = FKL_ladder_weight(
           begin_part+2, end_part-1,
           q0, pa, pb, p1, pn,
           lambda
       );
       return current_factor*ladder_factor;
     }
 
     template<class InIter, class partIter>
     double tree_kin_W_qqbar(InIter begin_in, partIter begin_part,
                             partIter end_part,
                             const CLHEP::HepLorentzVector & plbar,
                             const CLHEP::HepLorentzVector & pl,
                             double lambda, ParticleProperties const & Wprop
     ){
       const bool qbar_first=is_quark(*begin_part);
       const auto pa = to_HepLorentzVector(*begin_in);
       const auto pb = to_HepLorentzVector(*(begin_in+1));
       const auto pq = to_HepLorentzVector(*(begin_part+(qbar_first?0:1)));
       const auto pqbar = to_HepLorentzVector(*(begin_part+(qbar_first?1:0)));
       const auto p1 = to_HepLorentzVector(*(begin_part));
       const auto pn = to_HepLorentzVector(*(end_part-1));
 
       const bool wc = (begin_in+1)->type!=(end_part-1)->type; //leg b emits w
       auto q0 = pa - pq - pqbar;
       if(!wc)
         q0 -= pl + plbar;
 
       const double current_factor = ME_W_qqbar_current(
         (begin_in+1)->type, pa, pb,
         pq, pqbar, pn, plbar, pl, wc, Wprop
       );
 
       const double ladder_factor = FKL_ladder_weight(
           begin_part+2, end_part-1,
           q0, pa, pb, p1, pn,
           lambda
       );
       return current_factor*ladder_factor;
     }
 
     double tree_kin_W_qqbar_mid(
         ParticleID aptype, ParticleID bptype,
         CLHEP::HepLorentzVector const & pa,
         CLHEP::HepLorentzVector const & pb,
         std::vector<Particle> const & partons,
         CLHEP::HepLorentzVector const & plbar, CLHEP::HepLorentzVector const & pl,
         double lambda, ParticleProperties const & Wprop
     ){
       const auto backmidquark = std::find_if(
           begin(partons)+1, end(partons)-1,
           [](Particle const & s){ return s.type != pid::gluon; }
       );
 
       assert(backmidquark!=end(partons)-1);
 
       const bool qbar_first = is_antiquark(backmidquark->type);
 
       const auto pq    = to_HepLorentzVector(*(backmidquark+(qbar_first?1:0)));
       const auto pqbar = to_HepLorentzVector(*(backmidquark+(qbar_first?0:1)));
 
       const auto p1 = to_HepLorentzVector(partons.front());
       const auto pn = to_HepLorentzVector(partons.back());
 
       const auto begin_ladder_1 = cbegin(partons) + 1;
       const auto end_ladder_1   = (backmidquark);
       const auto begin_ladder_2 = (backmidquark+2);
       const auto end_ladder_2   = cend(partons) - 1;
 
       const int nabove = std::distance(begin_ladder_1, end_ladder_1);
       const int nbelow = std::distance(begin_ladder_2, end_ladder_2);
 
       const bool wqq = backmidquark->type != -(backmidquark+1)->type; // qqbar emit W
       const bool wc = !wqq && (aptype==partons.front().type); //leg b emits w
       assert(!wqq || !wc);
 
       auto q0 = pa - p1;
       // t-channel momentum after qqbar
       auto q3 = q0;
       if(wqq){ // emission from qqbar
         q3 -= pl + plbar;
       } else if(!wc) { // emission from leg a
         q0 -= pl + plbar;
         q3 -= pl + plbar;
       }
 
       for(auto parton_it = begin_ladder_1; parton_it != begin_ladder_2; ++parton_it){
         q3 -= to_HepLorentzVector(*parton_it);
       }
 
       std::vector<CLHEP::HepLorentzVector> partonsHLV;
       partonsHLV.reserve(partons.size());
       for(Particle const & parton: partons) {
         partonsHLV.push_back(to_HepLorentzVector(parton));
       }
 
       const double current_factor = ME_W_qqbar_mid_current(
           aptype, bptype, nabove, nbelow, pa, pb, partonsHLV,
           plbar, pl, qbar_first, wqq, wc, Wprop
       );
 
       const double ladder_factor = FKL_ladder_weight(
           begin_ladder_1, end_ladder_1,
           q0, pa, pb, p1, pn,
           lambda
       )*FKL_ladder_weight(
           begin_ladder_2, end_ladder_2,
           q3, pa, pb, p1, pn,
           lambda
         );
       return current_factor*ladder_factor;
     }
   } // namespace
 
   double MatrixElement::tree_kin_W(Event const & ev) const {
     using namespace event_type;
     auto const & incoming(ev.incoming());
 
   #ifndef NDEBUG
     // assert that there is exactly one decay corresponding to the W
     assert(ev.decays().size() == 1);
     auto const & w_boson{
       std::find_if(ev.outgoing().cbegin(), ev.outgoing().cend(),
         [] (Particle const & p) -> bool {
           return std::abs(p.type) == ParticleID::Wp;
         }) };
     assert(w_boson != ev.outgoing().cend());
     assert( static_cast<long int>(ev.decays().cbegin()->first)
         == std::distance(ev.outgoing().cbegin(), w_boson) );
   #endif
 
     // find decay products of W
     auto const & decay{ ev.decays().cbegin()->second };
     assert(decay.size() == 2);
     assert( ( is_anylepton(decay.at(0)) && is_anyneutrino(decay.at(1)) )
         || ( is_anylepton(decay.at(1)) && is_anyneutrino(decay.at(0)) ) );
 
     // get lepton & neutrino
     CLHEP::HepLorentzVector plbar;
     CLHEP::HepLorentzVector pl;
     if (decay.at(0).type < 0){
       plbar = to_HepLorentzVector(decay.at(0));
       pl = to_HepLorentzVector(decay.at(1));
     }
     else{
       pl = to_HepLorentzVector(decay.at(0));
       plbar = to_HepLorentzVector(decay.at(1));
     }
 
     const auto pa = to_HepLorentzVector(incoming[0]);
     const auto pb = to_HepLorentzVector(incoming[1]);
 
     const auto partons = tag_extremal_jet_partons(ev);
 
     if(ev.type() == FKL){
       return tree_kin_W_FKL(incoming[0].type, incoming[1].type,
                             pa, pb, partons, plbar, pl,
                             param_.regulator_lambda,
                             param_.ew_parameters.Wprop());
     }
     if(ev.type() == unordered_backward){
       return tree_kin_W_uno(cbegin(incoming), cbegin(partons),
                             cend(partons), plbar, pl,
                             param_.regulator_lambda,
                             param_.ew_parameters.Wprop());
     }
     if(ev.type() == unordered_forward){
       return tree_kin_W_uno(crbegin(incoming), crbegin(partons),
                             crend(partons), plbar, pl,
                             param_.regulator_lambda,
                             param_.ew_parameters.Wprop());
     }
     if(ev.type() == extremal_qqbar_backward){
       return tree_kin_W_qqbar(cbegin(incoming), cbegin(partons),
                               cend(partons), plbar, pl,
                               param_.regulator_lambda,
                               param_.ew_parameters.Wprop());
     }
     if(ev.type() == extremal_qqbar_forward){
       return tree_kin_W_qqbar(crbegin(incoming), crbegin(partons),
                               crend(partons), plbar, pl,
                               param_.regulator_lambda,
                               param_.ew_parameters.Wprop());
     }
     assert(ev.type() == central_qqbar);
     return tree_kin_W_qqbar_mid(incoming[0].type, incoming[1].type,
                                 pa, pb, partons, plbar, pl,
                                 param_.regulator_lambda,
                                 param_.ew_parameters.Wprop());
   }
 
   namespace /* WW */ {
     std::vector <double> tree_kin_WW_FKL(
         ParticleID aptype, ParticleID bptype,
         CLHEP::HepLorentzVector const & pa, CLHEP::HepLorentzVector const & pb,
         std::vector<Particle> const & partons,
         CLHEP::HepLorentzVector const & pl1bar, CLHEP::HepLorentzVector const & pl1,
         CLHEP::HepLorentzVector const & pl2bar, CLHEP::HepLorentzVector const & pl2,
         double lambda, ParticleProperties const & Wprop
     ){
       assert(is_anyquark(aptype));
       assert(is_anyquark(bptype));
 
       auto p1 = to_HepLorentzVector(partons[0]);
       auto pn = to_HepLorentzVector(partons[partons.size() - 1]);
 
       const std::vector <double> current_factor = ME_WW_current(
           aptype, bptype, pn, pb, p1, pa,
           pl1bar, pl1, pl2bar, pl2,
           Wprop
       );
 
       auto const begin_ladder = cbegin(partons) + 1;
       auto const end_ladder = cend(partons) - 1;
 
       // pa -> W1 p1, pb -> W2 + pn
       const auto q0 = pa - p1 - (pl1 + pl1bar);
       // pa -> W2 p1, pb -> W1 + pn
       const auto q1 = pa - p1 - (pl2 + pl2bar);
 
       const std::vector <double> ladder_factor = FKL_ladder_weight_mix(
         begin_ladder, end_ladder,
         q0, q1, pa, pb, p1, pn,
         lambda
       );
 
       assert(current_factor.size() == 3);
       assert(current_factor.size() == ladder_factor.size());
       std::vector<double> result(current_factor.size());
       for(size_t i=0; i<current_factor.size(); ++i){
         result[i] = K_q*K_q/(4.*(N_C*N_C - 1.))
           *current_factor.at(i)
           *ladder_factor.at(i);
       }
 
       const double t1_top = q0.m2();
       const double t2_top = (pb-pn-pl2bar-pl2).m2();
 
       const double t1_bot = q1.m2();
       const double t2_bot = (pb-pn-pl1bar-pl1).m2();
 
       result[0] /= t1_top * t2_top;
       result[1] /= t1_bot * t2_bot;
       result[2] /= sqrt(t1_top * t2_top * t1_bot * t2_bot);
       return result;
     }
   } // namespace
 
   std::vector <double> MatrixElement::tree_kin_WW(Event const & ev) const {
     using namespace event_type;
     auto const & incoming(ev.incoming());
 
     auto const pa = to_HepLorentzVector(incoming[0]);
     auto const pb = to_HepLorentzVector(incoming[1]);
 
     auto const partons = tag_extremal_jet_partons(ev);
 
     // W1 & W2
     assert(ev.decays().size() == 2);
 
     std::vector<CLHEP::HepLorentzVector> plbar;
     std::vector<CLHEP::HepLorentzVector> pl;
 
     for(auto const & decay_pair : ev.decays()) {
       auto const decay = decay_pair.second;
       // TODO: how to label W1, W2
       if(decay.at(0).type < 0) {
         plbar.emplace_back(to_HepLorentzVector(decay.at(0)));
         pl   .emplace_back(to_HepLorentzVector(decay.at(1)));
       }
       else {
         pl   .emplace_back(to_HepLorentzVector(decay.at(0)));
         plbar.emplace_back(to_HepLorentzVector(decay.at(1)));
       }
     }
 
     if(ev.type() == FKL) {
 
       return tree_kin_WW_FKL(
           incoming[0].type, incoming[1].type,
           pa, pb, partons,
           plbar[0], pl[0], plbar[1], pl[1],
           param_.regulator_lambda,
           param_.ew_parameters.Wprop()
       );
 
     }
     throw std::logic_error("Can only reweight FKL events in WW");
   }
 
   namespace{
     std::vector <double> tree_kin_Z_FKL(
         const ParticleID aptype, const ParticleID bptype,
         CLHEP::HepLorentzVector const & pa, CLHEP::HepLorentzVector const & pb,
         std::vector<Particle> const & partons,
         const ParticleID ltype,
         CLHEP::HepLorentzVector const & plbar, CLHEP::HepLorentzVector const & pl,
         const double lambda, ParticleProperties const & Zprop,
         const double stw2, const double ctw
     ){
       const auto p1 = to_HepLorentzVector(partons[0]);
       const auto pn = to_HepLorentzVector(partons[partons.size() - 1]);
 
       const auto begin_ladder = cbegin(partons) + 1;
       const auto end_ladder = cend(partons) - 1;
 
       const std::vector <double> current_factor = ME_Z_current(
           aptype, bptype, pn, pb, p1, pa,
           ltype, plbar, pl, Zprop, stw2, ctw
       );
 
       std::vector <double> ladder_factor;
       if(is_gluon(bptype)){
         // This is a qg event
         const auto q0 = pa-p1-plbar-pl;
         ladder_factor.push_back(FKL_ladder_weight(begin_ladder, end_ladder,
                                                   q0, pa, pb, p1, pn, lambda));
       } else if(is_gluon(aptype)){
         // This is a gq event
         const auto q0 = pa-p1;
         ladder_factor.push_back(FKL_ladder_weight(begin_ladder, end_ladder,
                                                   q0, pa, pb, p1, pn, lambda));
       } else {
         // This is a qq event
         const auto q0 = pa-p1-plbar-pl;
         const auto q1 = pa-p1;
         ladder_factor=FKL_ladder_weight_mix(begin_ladder, end_ladder,
                                             q0, q1, pa, pb, p1, pn, lambda);
       }
 
       std::vector <double> result;
       for(size_t i=0; i<current_factor.size(); ++i){
         result.push_back(current_factor.at(i)*ladder_factor.at(i));
       }
       return result;
     }
 
     template<class InIter, class partIter>
     std::vector <double> tree_kin_Z_uno(
       InIter begin_in, partIter begin_part, partIter end_part,
       const ParticleID ltype,
       const CLHEP::HepLorentzVector & plbar,
       const CLHEP::HepLorentzVector & pl,
       const double lambda, ParticleProperties const & Zprop,
       const double stw2, const double ctw
     ){
       const auto pa = to_HepLorentzVector(*begin_in);
       const auto pb = to_HepLorentzVector(*(begin_in+1));
 
       const auto pg = to_HepLorentzVector(*begin_part);
       const auto p1 = to_HepLorentzVector(*(begin_part+1));
       const auto pn = to_HepLorentzVector(*(end_part-1));
 
       const ParticleID aptype = (begin_in)->type;
       const ParticleID bptype = (begin_in+1)->type;
 
       // we only evaluate unordered backward -> first incoming particle must be a quark
       assert(is_anyquark(aptype));
 
       const std::vector <double> current_factor = ME_Z_uno_current(
           aptype, bptype, pn, pb, p1, pa, pg,
           ltype, plbar, pl, Zprop, stw2, ctw
       );
 
       std::vector <double> ladder_factor;
       const auto q0 = pa-pg-p1-plbar-pl;
       if(is_gluon(bptype)){
         // This is a qg event
         ladder_factor.push_back(FKL_ladder_weight(begin_part+2, end_part-1,
                                                   q0, pa, pb, p1, pn, lambda));
       }else{
         // This is a qq event
         const auto q1 = pa-pg-p1;
         ladder_factor=FKL_ladder_weight_mix(begin_part+2, end_part-1,
                                             q0, q1, pa, pb, p1, pn, lambda);
       }
 
       std::vector <double> result;
       for(size_t i=0; i<current_factor.size(); ++i){
         result.push_back(current_factor.at(i)*ladder_factor.at(i));
       }
       return result;
     }
 
     template<class InIter, class partIter>
     std::vector <double> tree_kin_Z_qqbar(
       InIter begin_in, partIter begin_part, partIter end_part,
       const ParticleID ltype,
       const CLHEP::HepLorentzVector & plbar,
       const CLHEP::HepLorentzVector & pl,
       const double lambda, ParticleProperties const & Zprop,
       const double stw2, const double ctw
     ){
       const bool qbar_first = is_antiquark(*begin_part);
 
       const auto pa = to_HepLorentzVector(*begin_in);
       const auto pb = to_HepLorentzVector(*(begin_in+1));
 
       const auto pq    = to_HepLorentzVector(*(begin_part+(qbar_first?1:0)));
       const auto pqbar = to_HepLorentzVector(*(begin_part+(qbar_first?0:1)));
 
       const auto p1 = to_HepLorentzVector(*(begin_part));
       const auto pn = to_HepLorentzVector(*(end_part-1));
 
       const ParticleID qptype = (begin_part+(qbar_first?1:0))->type;
       const ParticleID bptype = (begin_in+1)->type;
 
       const std::vector <double> current_factor = ME_Z_exqqbar_current(
           qptype, bptype, pa, pb, pq, pqbar, pn,
           ltype, plbar, pl, Zprop, stw2, ctw
       );
 
       std::vector <double> ladder_factor;
       const auto q0 = pa-pq-pqbar-plbar-pl;
       if(is_gluon(bptype)){
         // This is a gg event
         ladder_factor.push_back(FKL_ladder_weight(begin_part+2, end_part-1,
                                                   q0, pa, pb, p1, pn, lambda));
       }else{
         // This is a gq event
         const auto q1 = pa-pq-pqbar;
         ladder_factor=FKL_ladder_weight_mix(begin_part+2, end_part-1,
                                             q0, q1, pa, pb, p1, pn, lambda);
       }
 
       std::vector <double> result;
       for(size_t i=0; i<current_factor.size(); ++i){
         result.push_back(current_factor.at(i)*ladder_factor.at(i));
       }
       return result;
     }
 
     template<class InIter, class partIter>
     std::vector<double> tree_kin_Z_qqbar_mid(
       InIter begin_in, partIter begin_part, partIter end_part,
       const ParticleID ltype,
       const CLHEP::HepLorentzVector & plbar,
       const CLHEP::HepLorentzVector & pl,
       const double lambda, ParticleProperties const & Zprop,
       const double stw2, const double ctw
     ){
       const ParticleID aptype = (begin_in)->type;
       const ParticleID bptype = (begin_in+1)->type;
 
       const auto pa = to_HepLorentzVector(*begin_in);
       const auto pb = to_HepLorentzVector(*(begin_in+1));
 
       const auto backmidquark = std::find_if(
           begin_part+1, end_part-1,
           [](Particle const & s){ return s.type != pid::gluon; }
       );
 
       assert(backmidquark!=end_part-1);
 
       const bool qbar_first = is_antiquark(backmidquark->type);
 
       const auto pq    = to_HepLorentzVector(*(backmidquark+(qbar_first?1:0)));
       const auto pqbar = to_HepLorentzVector(*(backmidquark+(qbar_first?0:1)));
 
       const ParticleID qptype = (backmidquark+(qbar_first?1:0))->type;
 
       const auto p1 = to_HepLorentzVector(*(begin_part));
       const auto pn = to_HepLorentzVector(*(end_part-1));
 
       const auto begin_ladder_1 = begin_part + 1;
       const auto end_ladder_1   = (backmidquark);
       const auto begin_ladder_2 = (backmidquark+2);
       const auto end_ladder_2   = end_part - 1;
 
       const int nabove = std::distance(begin_ladder_1, end_ladder_1);
 
       std::vector<CLHEP::HepLorentzVector> partonsHLV;
       partonsHLV.reserve(std::distance(begin_part, end_part));
       for(auto parton_it = begin_part; parton_it != end_part; ++parton_it){
         partonsHLV.push_back(to_HepLorentzVector(*parton_it));
       }
 
       const std::vector<double> current_factor = ME_Z_qqbar_mid_current(
           aptype, bptype, qptype, qbar_first, nabove, pa, pb,
           partonsHLV, ltype, plbar, pl, Zprop, stw2, ctw
       );
 
       std::vector<double> ladder_factor;
       if(is_gluon(aptype)) {
         if(is_gluon(bptype)) {
           // gg event -> Z emitted from central qqbar
 
           // first t-channel momentum
           const auto q0 = pa - p1;
 
           // t-channel momentum after qqbar
           auto q3 = q0 - pl - plbar;
           for(auto parton_it = begin_ladder_1; parton_it != begin_ladder_2; ++parton_it){
             q3 -= to_HepLorentzVector(*parton_it);
           }
 
           ladder_factor.push_back(
               FKL_ladder_weight(begin_ladder_1, end_ladder_1, q0, pa, pb, p1, pn, lambda)
               * FKL_ladder_weight(begin_ladder_2, end_ladder_2, q3, pa, pb, p1, pn, lambda)
           );
         } else {
           // gq event -> Z emitted from central qqbar or bottom leg
 
           auto q_bot = pa - p1;
 
           // q0_mid = q0_bot -> no need to evaluate FKL_ladder_weight_mix for the first ladder
           const double ladder_1 = FKL_ladder_weight(begin_ladder_1, end_ladder_1,
                                                     q_bot, pa, pb, p1, pn, lambda);
 
           for(auto parton_it = begin_ladder_1; parton_it != begin_ladder_2; ++parton_it) {
             q_bot -= to_HepLorentzVector(*parton_it);
           }
           auto q_mid = q_bot - pl - plbar;
 
           const auto ladder_2 = FKL_ladder_weight_mix(begin_ladder_2, end_ladder_2,
                                                       q_mid, q_bot, pa, pb, p1, pn, lambda);
 
           for(size_t i=0; i<ladder_2.size(); ++i){
             ladder_factor.push_back(ladder_1 * ladder_2.at(i));
           }
         }
       } else {
         assert(is_anyquark(bptype));
         // qq event -> 3 contributions
 
         auto q_t = pa - p1 - pl - plbar;
         auto q_b = pa - p1;
 
         // q0_bot = q0_mid -> only need to evaluate FKL_ladder_weight_mix[top][mid]
         const auto ladder_1_top_mid = FKL_ladder_weight_mix(begin_ladder_1, end_ladder_1,
                                                             q_t, q_b, pa, pb, p1, pn, lambda);
 
         enum emission_site {top, mid, bot};
 
         double ladder[3][3];
         ladder[top][top] = ladder_1_top_mid.at(0);
         ladder[mid][mid] = ladder_1_top_mid.at(1);
         ladder[bot][bot] = ladder[mid][mid];
 
         ladder[top][mid] = ladder_1_top_mid.at(2);
         ladder[top][bot] = ladder[top][mid];
         ladder[mid][bot] = ladder[mid][mid];
 
         for(auto parton_it = begin_ladder_1; parton_it != begin_ladder_2; ++parton_it) {
           q_b -= to_HepLorentzVector(*parton_it);
         }
         q_t = q_b - pl - plbar;
 
         // q3_mid = q3_top -> only need to evaluate FKL_ladder_weight_mix[top][bot]
         const auto ladder_2_top_bot = FKL_ladder_weight_mix(begin_ladder_2, end_ladder_2,
                                                             q_t, q_b, pa, pb, p1, pn, lambda);
 
         ladder[top][top] *= ladder_2_top_bot.at(0);
         ladder[mid][mid] *= ladder_2_top_bot.at(0); // same as [top][top]
         ladder[bot][bot] *= ladder_2_top_bot.at(1);
 
         ladder[top][mid] *= ladder_2_top_bot.at(0); // same as [top][top]
         ladder[top][bot] *= ladder_2_top_bot.at(2);
         ladder[mid][bot] *= ladder_2_top_bot.at(2); // same as [top][bot]
 
         ladder_factor = {ladder[top][top], ladder[mid][mid], ladder[bot][bot],
                          ladder[top][mid], ladder[top][bot], ladder[mid][bot]};
       }
       assert(current_factor.size() == ladder_factor.size());
 
       std::vector<double> res;
       for(size_t i=0; i<current_factor.size(); ++i) {
         res.push_back(current_factor.at(i)*ladder_factor.at(i));
       }
       return res;
     }
   } // namespace
 
   std::vector<double> MatrixElement::tree_kin_Z(Event const & ev) const {
     using namespace event_type;
     auto const & incoming(ev.incoming());
 
     // find decay products of Z
     auto const & decay{ ev.decays().cbegin()->second };
     assert(decay.size() == 2);
     assert(is_anylepton(decay.at(0)) && decay.at(0).type==-decay.at(1).type);
 
     // get leptons
     CLHEP::HepLorentzVector plbar;
     CLHEP::HepLorentzVector pl;
     ParticleID ltype;
     if (decay.at(0).type < 0){
       plbar = to_HepLorentzVector(decay.at(0));
       pl = to_HepLorentzVector(decay.at(1));
       ltype = decay.at(1).type;
     }
     else{
       pl = to_HepLorentzVector(decay.at(0));
       ltype = decay.at(0).type;
       plbar = to_HepLorentzVector(decay.at(1));
     }
 
     const auto pa = to_HepLorentzVector(incoming[0]);
     const auto pb = to_HepLorentzVector(incoming[1]);
 
     const auto partons = tag_extremal_jet_partons(ev);
 
     const double stw2 = param_.ew_parameters.sin2_tw();
     const double ctw  = param_.ew_parameters.cos_tw();
 
     if(ev.type() == FKL){
       return tree_kin_Z_FKL(incoming[0].type, incoming[1].type,
                             pa, pb, partons, ltype, plbar, pl,
                             param_.regulator_lambda,
                             param_.ew_parameters.Zprop(),
                             stw2, ctw);
     }
     if(ev.type() == unordered_backward){
       return tree_kin_Z_uno(cbegin(incoming), cbegin(partons),
                             cend(partons), ltype, plbar, pl,
                             param_.regulator_lambda,
                             param_.ew_parameters.Zprop(),
                             stw2, ctw);
     }
     if(ev.type() == unordered_forward){
       auto kin_rev = tree_kin_Z_uno(crbegin(incoming), crbegin(partons),
                                     crend(partons), ltype, plbar, pl,
                                     param_.regulator_lambda,
                                     param_.ew_parameters.Zprop(),
                                     stw2, ctw);
       if(!is_gluon(incoming[0].type)){
         // qq unordered forward: reorder contributions such that first/second
         // value corresponds to Z emission from top/bottom leg respectively
         std::swap(kin_rev[0], kin_rev[1]);
       }
       return kin_rev;
     }
     if(ev.type() == extremal_qqbar_backward){
       return tree_kin_Z_qqbar(cbegin(incoming), cbegin(partons),
                               cend(partons), ltype, plbar, pl,
                               param_.regulator_lambda,
                               param_.ew_parameters.Zprop(),
                               stw2, ctw);
     }
     if(ev.type() == extremal_qqbar_forward){
       auto kin_rev = tree_kin_Z_qqbar(crbegin(incoming), crbegin(partons),
                                       crend(partons), ltype, plbar, pl,
                                       param_.regulator_lambda,
                                       param_.ew_parameters.Zprop(),
                                       stw2, ctw);
       if(!is_gluon(incoming[0].type)){
         // qqbar forward with incoming qg: reorder contributions such that first/second
         // value corresponds to Z emission from top/bottom leg respectively
         std::swap(kin_rev[0], kin_rev[1]);
       }
       return kin_rev;
     }
     assert(ev.type() == central_qqbar);
     if(!is_gluon(incoming[0].type) && is_gluon(incoming[1].type)){
       // qg initiated central qqbar: reverse event to evaluate as gq
       auto kin_rev = tree_kin_Z_qqbar_mid(crbegin(incoming), crbegin(partons),
                                           crend(partons), ltype, plbar, pl,
                                           param_.regulator_lambda,
                                           param_.ew_parameters.Zprop(),
                                           stw2, ctw);
       std::swap(kin_rev[0], kin_rev[1]);
       return kin_rev;
     }
     return tree_kin_Z_qqbar_mid(cbegin(incoming), cbegin(partons),
                                 cend(partons), ltype, plbar, pl,
                                 param_.regulator_lambda,
                                 param_.ew_parameters.Zprop(),
                                 stw2, ctw);
   }
 
   double MatrixElement::tree_kin_Higgs(Event const & ev) const {
     if(ev.outgoing().front().type == pid::Higgs){
       return tree_kin_Higgs_first(ev);
     }
     if(ev.outgoing().back().type == pid::Higgs){
       return tree_kin_Higgs_last(ev);
     }
     return tree_kin_Higgs_between(ev);
   }
 
   // kinetic matrix element square for backward Higgs emission
   // cf. eq:ME_h_jets_peripheral in developer manual,
   // but without factors \alpha_s and the FKL ladder
   double MatrixElement::MH2_backwardH(
     const ParticleID type_forward,
     CLHEP::HepLorentzVector const & pa,
     CLHEP::HepLorentzVector const & pb,
     CLHEP::HepLorentzVector const & pH,
     CLHEP::HepLorentzVector const & pn
   ) const {
     using namespace currents;
     const double vev = param_.ew_parameters.vev();
     return K(type_forward, pn, pb)*ME_H_gq(
       pH, pa, pn, pb,
       param_.Higgs_coupling.mt, param_.Higgs_coupling.include_bottom,
       param_.Higgs_coupling.mb, vev
     )/(4.*(N_C*N_C - 1)*(pa-pH).m2()*(pb-pn).m2());
   }
 
   // kinetic matrix element square for backward unordered emission
   // and forward g -> Higgs
   double MatrixElement::MH2_unob_forwardH(
     CLHEP::HepLorentzVector const & pa,
     CLHEP::HepLorentzVector const & pb,
     CLHEP::HepLorentzVector const & pg,
     CLHEP::HepLorentzVector const & p1,
     CLHEP::HepLorentzVector const & pH
   ) const {
     using namespace currents;
     const double vev = param_.ew_parameters.vev();
 
     constexpr double K_f1 = K_q;
 
     constexpr double nhel = 4.;
 
     return K_f1*ME_juno_jgH(
       pg, p1, pa, pH, pb,
       param_.Higgs_coupling.mt, param_.Higgs_coupling.include_bottom,
       param_.Higgs_coupling.mb, vev
     )/(nhel*(N_C*N_C - 1)*(pa - p1 - pg).m2()*(pb - pH).m2());
   }
 
   double MatrixElement::tree_kin_Higgs_first(Event const & ev) const {
     auto const & incoming = ev.incoming();
     auto const & outgoing = ev.outgoing();
     assert(outgoing.front().type == pid::Higgs);
 
     if(is_anyquark(incoming.front())) {
       assert(incoming.front().type == outgoing[1].type);
       return tree_kin_Higgs_between(ev);
     }
 
     const auto partons = tag_extremal_jet_partons(ev);
 
     const auto pa = to_HepLorentzVector(incoming.front());
     const auto pb = to_HepLorentzVector(incoming.back());
 
     const auto pH = to_HepLorentzVector(outgoing.front());
 
     const auto end_ladder = end(partons) - ((ev.type() == event_type::unof)?2:1);
     const auto pn = to_HepLorentzVector(*end_ladder);
 
     const double ladder = FKL_ladder_weight(
         begin(partons), end_ladder,
         pa - pH, pa, pb, pa, pn,
         param_.regulator_lambda
     );
 
     if(ev.type() == event_type::unof) {
       const auto pg = to_HepLorentzVector(outgoing.back());
       return MH2_unob_forwardH(
         pb, pa, pg, pn, pH
       )*ladder;
     }
 
     return MH2_backwardH(
       incoming.back().type,
       pa, pb, pH, pn
     )*ladder;
   }
 
   double MatrixElement::tree_kin_Higgs_last(Event const & ev) const {
     auto const & incoming = ev.incoming();
     auto const & outgoing = ev.outgoing();
     assert(outgoing.back().type == pid::Higgs);
 
     if(is_anyquark(incoming.back())) {
       assert(incoming.back().type == outgoing[outgoing.size()-2].type);
       return tree_kin_Higgs_between(ev);
     }
 
     const auto partons = tag_extremal_jet_partons(ev);
 
     const auto pa = to_HepLorentzVector(incoming.front());
     const auto pb = to_HepLorentzVector(incoming.back());
 
     const auto pH = to_HepLorentzVector(outgoing.back());
 
     auto begin_ladder = begin(partons) + 1;
     auto q0 = pa - to_HepLorentzVector(partons.front());
     if(ev.type() == event_type::unob) {
       q0 -= to_HepLorentzVector(*begin_ladder);
       ++begin_ladder;
     }
     const auto p1 = to_HepLorentzVector(*(begin_ladder - 1));
 
     const double ladder = FKL_ladder_weight(
         begin_ladder, end(partons),
         q0, pa, pb, p1, pb,
         param_.regulator_lambda
     );
 
     if(ev.type() == event_type::unob) {
       const auto pg = to_HepLorentzVector(outgoing.front());
       return MH2_unob_forwardH(
         pa, pb, pg, p1, pH
       )*ladder;
     }
 
     return MH2_backwardH(
       incoming.front().type,
       pb, pa, pH, p1
     )*ladder;
   }
 
   namespace {
     template<class InIter, class partIter>
     double tree_kin_Higgs_uno(InIter begin_in, InIter end_in, partIter begin_part,
                               partIter end_part,
                               CLHEP::HepLorentzVector const & qH,
                               CLHEP::HepLorentzVector const & qHp1,
                               double mt, bool inc_bot, double mb, double vev
     ){
 
       const auto pa = to_HepLorentzVector(*begin_in);
       const auto pb = to_HepLorentzVector(*(end_in-1));
 
       const auto pg = to_HepLorentzVector(*begin_part);
       const auto p1 = to_HepLorentzVector(*(begin_part+1));
       const auto pn = to_HepLorentzVector(*(end_part-1));
 
       return ME_Higgs_current_uno(
         (begin_in)->type, (end_in-1)->type, pg, pn, pb, p1, pa,
         qH, qHp1, mt, inc_bot, mb, vev
         );
     }
   } // namespace
 
 
   double MatrixElement::tree_kin_Higgs_between(Event const & ev) const {
     using namespace event_type;
     auto const & incoming = ev.incoming();
     auto const & outgoing = ev.outgoing();
 
     const auto the_Higgs = std::find_if(
         begin(outgoing), end(outgoing),
         [](Particle const & s){ return s.type == pid::Higgs; }
     );
     assert(the_Higgs != end(outgoing));
     const auto pH = to_HepLorentzVector(*the_Higgs);
     const auto partons = tag_extremal_jet_partons(ev);
 
     const auto pa = to_HepLorentzVector(incoming[0]);
     const auto pb = to_HepLorentzVector(incoming[1]);
 
     auto p1 = to_HepLorentzVector(
         partons[(ev.type() == unob)?1:0]
     );
     auto pn = to_HepLorentzVector(
         partons[partons.size() - ((ev.type() == unof)?2:1)]
     );
 
     auto first_after_Higgs = begin(partons) + (the_Higgs-begin(outgoing));
     assert(
         (first_after_Higgs == end(partons) && (
             (ev.type() == unob)
             || partons.back().type != pid::gluon
         ))
         || first_after_Higgs->rapidity() >= the_Higgs->rapidity()
     );
     assert(
         (first_after_Higgs == begin(partons) && (
             (ev.type() == unof)
             || partons.front().type != pid::gluon
         ))
         || (first_after_Higgs-1)->rapidity() <= the_Higgs->rapidity()
     );
     // always treat the Higgs as if it were in between the extremal FKL partons
     if(first_after_Higgs == begin(partons)) ++first_after_Higgs;
     else if(first_after_Higgs == end(partons)) --first_after_Higgs;
 
     // t-channel momentum before Higgs
     auto qH = pa;
     for(auto parton_it = begin(partons); parton_it != first_after_Higgs; ++parton_it){
       qH -= to_HepLorentzVector(*parton_it);
     }
 
     auto q0 = pa - p1;
     auto begin_ladder = begin(partons) + 1;
     auto end_ladder = end(partons) - 1;
 
     double current_factor = NAN;
     if(ev.type() == FKL){
       current_factor = ME_Higgs_current(
           incoming[0].type, incoming[1].type,
           pn, pb, p1, pa, qH, qH - pH,
           param_.Higgs_coupling.mt,
           param_.Higgs_coupling.include_bottom, param_.Higgs_coupling.mb,
           param_.ew_parameters.vev()
       );
     }
     else if(ev.type() == unob){
       current_factor = tree_kin_Higgs_uno(
         begin(incoming), end(incoming), begin(partons),
         end(partons), qH, qH-pH, param_.Higgs_coupling.mt,
         param_.Higgs_coupling.include_bottom, param_.Higgs_coupling.mb,
         param_.ew_parameters.vev()
         );
       const auto p_unob = to_HepLorentzVector(partons.front());
       q0 -= p_unob;
       p1 += p_unob;
       ++begin_ladder;
     }
     else if(ev.type() == unof){
       current_factor = tree_kin_Higgs_uno(
         rbegin(incoming), rend(incoming), rbegin(partons),
         rend(partons), qH-pH, qH, param_.Higgs_coupling.mt,
         param_.Higgs_coupling.include_bottom, param_.Higgs_coupling.mb,
         param_.ew_parameters.vev()
         );
       pn += to_HepLorentzVector(partons.back());
       --end_ladder;
     }
     else{
       throw std::logic_error("Can only reweight FKL or uno processes in H+Jets");
     }
 
     const double ladder_factor = FKL_ladder_weight(
         begin_ladder, first_after_Higgs,
         q0, pa, pb, p1, pn,
         param_.regulator_lambda
     )*FKL_ladder_weight(
         first_after_Higgs, end_ladder,
         qH - pH, pa, pb, p1, pn,
         param_.regulator_lambda
     );
     return current_factor/(4.*(N_C*N_C-1.))*ladder_factor;
   }
 
   namespace {
     double get_AWZH_coupling(Event const & ev, double alpha_s, double alpha_w) {
       std::vector<Particle> bosons = filter_AWZH_bosons(ev.outgoing());
 
       if(bosons.empty()) {
         return 1.;
       }
 
       if(bosons.size() == 1) {
         switch(bosons[0].type){
         case pid::Higgs:
           return alpha_s*alpha_s;
         case pid::Wp:
         case pid::Wm:
           return alpha_w*alpha_w;
+        case pid::Z:
         case pid::Z_photon_mix:
           return alpha_w*alpha_w;
         // TODO
         case pid::photon:
-        case pid::Z:
         default:
           throw not_implemented("Emission of boson of unsupported type");
         }
       }
 
       if(bosons.size() == 2) {
         if(bosons[0].type == pid::Wp && bosons[1].type == pid::Wp) {
           return alpha_w*alpha_w*alpha_w*alpha_w;
         }
         else if(bosons[0].type == pid::Wm && bosons[1].type == pid::Wm) {
           return alpha_w*alpha_w*alpha_w*alpha_w;
         }
 
         throw not_implemented("Emission of bosons of unsupported type");
       }
 
 
       throw not_implemented("Emission of >2 bosons is unsupported");
     }
   } // namespace
 
   double MatrixElement::tree_param(Event const & ev, double mur) const {
     assert(is_resummable(ev.type()));
 
     const auto begin_partons = ev.begin_partons();
     const auto end_partons = ev.end_partons();
     const auto num_partons = std::distance(begin_partons, end_partons);
     const double alpha_s = alpha_s_(mur);
     const double gs2 = 4.*M_PI*alpha_s;
     double res = std::pow(gs2, num_partons);
     if(param_.log_correction){
       // use alpha_s(q_perp), evolved to mur
       assert(num_partons >= 2);
       const auto first_emission = std::next(begin_partons);
       const auto last_emission = std::prev(end_partons);
       for(auto parton = first_emission; parton != last_emission; ++parton){
         res *= 1. + alpha_s/(2.*M_PI)*BETA0*std::log(mur/parton->perp());
       }
     }
     return get_AWZH_coupling(ev, alpha_s, param_.ew_parameters.alpha_w())*res;
   }
 
 } // namespace HEJ
diff --git a/t/ME_data/ME_Z_neutrinos.dat b/t/ME_data/ME_Z_neutrinos.dat
index 421e467..a07a1d7 100644
--- a/t/ME_data/ME_Z_neutrinos.dat
+++ b/t/ME_data/ME_Z_neutrinos.dat
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:996c87f8837c224735955c624ab956fe9ba6d77c925d94f0f6157d593813bfba
+oid sha256:9bfce3b3ed8fc682317e5691615bc8c1735ab11e3a88016aa1246fdf21e64db8
 size 160000