diff --git a/FixedOrderGen/include/PhaseSpacePoint.hh b/FixedOrderGen/include/PhaseSpacePoint.hh index 4399492..01d3363 100644 --- a/FixedOrderGen/include/PhaseSpacePoint.hh +++ b/FixedOrderGen/include/PhaseSpacePoint.hh @@ -1,322 +1,329 @@ /** \file PhaseSpacePoint.hh * \brief Contains the PhaseSpacePoint Class * * \authors The HEJ collaboration (see AUTHORS for details) * \date 2019-2020 * \copyright GPLv2 or later */ #pragma once #include #include #include #include #include #include #include "boost/iterator/filter_iterator.hpp" #include "HEJ/Event.hh" #include "HEJ/PDG_codes.hh" #include "HEJ/Particle.hh" #include "fastjet/PseudoJet.hh" #include "Decay.hh" #include "Status.hh" #include "Subleading.hh" namespace HEJ { class EWConstants; class PDF; class RNG; } namespace HEJFOG { struct JetParameters; struct Process; //! A point in resummation phase space class PhaseSpacePoint{ public: //! Iterator over partons using ConstPartonIterator = boost::filter_iterator< bool (*)(HEJ::Particle const &), std::vector::const_iterator >; //! Reverse Iterator over partons using ConstReversePartonIterator = std::reverse_iterator< ConstPartonIterator>; //! Default PhaseSpacePoint Constructor PhaseSpacePoint() = delete; //! PhaseSpacePoint Constructor /** * @param proc The process to generate * @param jet_param Jet defintion & cuts * @param pdf The pdf set (used for sampling) * @param E_beam Energie of the beam * @param subl_chance Chance to turn a potentially unordered * emission into an actual one * @param subl_channels Possible subleading channels. * see HEJFOG::Subleading * @param particle_properties Properties of producted boson * * Initially, only FKL phase space points are generated. subl_chance gives * the chance of turning one emissions into a subleading configuration, * i.e. either unordered or central quark/anti-quark pair. Unordered * emissions require that the most extremal emission in any direction is * a quark or anti-quark and the next emission is a gluon. Quark/anti-quark * pairs are only generated for W processes. At most one subleading * emission will be generated in this way. */ PhaseSpacePoint( Process const & proc, JetParameters const & jet_param, HEJ::PDF & pdf, double E_beam, double subl_chance, Subleading subl_channels, ParticlesDecayMap const & particle_decays, HEJ::EWConstants const & ew_parameters, HEJ::RNG & ran ); //! Get Weight Function /** * @returns Weight of Event */ double weight() const{ return weight_; } Status status() const{ return status_; } //! Get Incoming Function /** * @returns Incoming Particles */ std::array const & incoming() const{ return incoming_; } //! Get Outgoing Function /** * @returns Outgoing Particles */ std::vector const & outgoing() const{ return outgoing_; } std::unordered_map> const & decays() const{ return decays_; } //! Iterator to the first outgoing parton ConstPartonIterator begin_partons() const; //! Iterator to the first outgoing parton ConstPartonIterator cbegin_partons() const; //! Iterator to the end of the outgoing partons ConstPartonIterator end_partons() const; //! Iterator to the end of the outgoing partons ConstPartonIterator cend_partons() const; //! Reverse Iterator to the first outgoing parton ConstReversePartonIterator rbegin_partons() const; //! Reverse Iterator to the first outgoing parton ConstReversePartonIterator crbegin_partons() const; //! Reverse Iterator to the first outgoing parton ConstReversePartonIterator rend_partons() const; //! Reverse Iterator to the first outgoing parton ConstReversePartonIterator crend_partons() const; private: static constexpr std::size_t NUM_PARTONS = 11; //!< Number of partons public: using part_mask = std::bitset; //!< Selection mask for partons private: friend HEJ::Event::EventData to_EventData(PhaseSpacePoint psp); /** * @internal * @brief Generate LO parton momentum * * @param np Number of partons to generate * @param is_pure_jets If true ensures momentum conservation in x and y * @param jet_param Jet properties to fulfil * @param max_pt max allowed pt for a parton (typically E_CMS) * @param ran Random Number Generator * * @returns Momentum of partons * * Ensures that each parton is in its own jet. * Generation is independent of parton flavour. Output is sorted in rapidity. */ std::vector gen_LO_partons( int np, bool is_pure_jets, JetParameters const & jet_param, double max_pt, HEJ::RNG & ran ); + void add_boson( + Process const & proc, + std::optional channel, + ParticlesDecayMap const & particle_decays, + HEJ::EWConstants const & ew_parameters, + HEJ::RNG & ran + ); HEJ::Particle gen_boson( HEJ::ParticleID bosonid, double mass, double width, Process const & proc, std::optional channel, HEJ::RNG & ran ); double gen_V_boson_rapidity(HEJ::RNG & ran); double gen_Higgs_rapidity( Process const & proc, std::optional channel, HEJ::RNG & ran ); template fastjet::PseudoJet gen_last_momentum( ParticleMomenta const & other_momenta, double mass_square, double y ) const; bool jets_ok( std::vector const & Born_jets, std::vector const & partons ) const; /** * @internal * @brief Generate incoming partons according to the PDF * * @param uf Scale used in the PDF */ void reconstruct_incoming( Process const & proc, std::optional channel, HEJ::PDF & pdf, double E_beam, double uf, HEJ::RNG & ran ); HEJ::ParticleID generate_incoming_id( std::size_t beam_idx, double x, double uf, HEJ::PDF & pdf, part_mask allowed_partons, HEJ::RNG & ran ); //! @brief Returns list of all allowed initial states partons std::array allowed_incoming( Process const & proc, std::optional channel, HEJ::RNG & ran ); //! Ensure that incoming state compatible with A/W/Z production //! Should not be called for final-state qqbar configurations, //! since A/W/Z emission doesn't constrain the initial state there std::array incoming_AWZ( Process const & proc, std::array allowed_partons, HEJ::RNG & ran ); //! Ensure that incoming state compatible with extremal qqbar std::array incoming_eqqbar( std::array allowed_partons, HEJ::RNG & ran); //! Ensure that incoming state compatible with unordered std::array incoming_uno( std::array allowed_partons, HEJ::RNG & ran); bool momentum_conserved(double ep) const; bool extremal_FKL_ok( std::vector const & partons ) const; double random_normal(double stddev, HEJ::RNG & ran); double random_normal_trunc( double stddev, HEJ::RNG & ran, double min, double max ); /** * @internal * @brief Turns a FKL configuration into a subleading one * * @param chance Chance to switch to subleading configuration * @param channels Allowed channels for subleading process * @param proc Process to decide which subleading * configurations are allowed * * With a chance of "chance" the FKL configuration is either turned into * a unordered configuration or, for A/W/Z bosons, a configuration with * a central quark/anti-quark pair. */ void turn_to_subl( subleading::Channels channel, Process const & proc, HEJ::RNG & ran ); void turn_to_subl( Subleading channels, bool can_be_uno_backward, bool can_be_uno_forward, bool allow_strange, HEJ::RNG & ran); void turn_to_uno(bool can_be_uno_backward, bool can_be_uno_forward, HEJ::RNG & ran); HEJ::ParticleID select_qqbar_flavour(bool allow_strange, HEJ::RNG & ran); void turn_to_cqqbar(bool allow_strange, HEJ::RNG & ran); void turn_to_eqqbar(bool allow_strange, HEJ::RNG & ran); //! decay where we select the decay channel std::vector decay_channel( HEJ::Particle const & parent, std::vector const & decays, HEJ::RNG & ran ); /// @brief setup outgoing partons to ensure correct coupling to boson void couple_boson(HEJ::ParticleID boson, HEJ::RNG & ran); Decay select_decay_channel( std::vector const & decays, HEJ::RNG & ran ); double gen_hard_pt( int np, double ptmin, double ptmax, double y, HEJ::RNG & ran ); double gen_soft_pt(int np, double max_pt, HEJ::RNG & ran); double gen_parton_pt( int count, JetParameters const & jet_param, double max_pt, double y, HEJ::RNG & ran ); //! Iterator over partons (non-const) using PartonIterator = boost::filter_iterator< bool (*)(HEJ::Particle const &), std::vector::iterator >; //! Reverse Iterator over partons (non-const) using ReversePartonIterator = std::reverse_iterator; //! Iterator to the first outgoing parton (non-const) PartonIterator begin_partons(); //! Iterator to the end of the outgoing partons (non-const) PartonIterator end_partons(); //! Reverse Iterator to the first outgoing parton (non-const) ReversePartonIterator rbegin_partons(); //! Reverse Iterator to the first outgoing parton (non-const) ReversePartonIterator rend_partons(); std::optional select_channel( Subleading subl_channels, double chance, HEJ::RNG & ran ); double weight_; Status status_; std::array incoming_; std::vector outgoing_; //! Particle decays in the format {outgoing index, decay products} std::unordered_map> decays_; }; //! Extract HEJ::Event::EventData from PhaseSpacePoint HEJ::Event::EventData to_EventData(PhaseSpacePoint psp); } // namespace HEJFOG diff --git a/FixedOrderGen/src/PhaseSpacePoint.cc b/FixedOrderGen/src/PhaseSpacePoint.cc index 7ba2e7b..b7af771 100644 --- a/FixedOrderGen/src/PhaseSpacePoint.cc +++ b/FixedOrderGen/src/PhaseSpacePoint.cc @@ -1,1032 +1,1042 @@ /** * \authors The HEJ collaboration (see AUTHORS for details) * \date 2019-2020 * \copyright GPLv2 or later */ #include "PhaseSpacePoint.hh" #include #include #include #include #include #include #include #include #include #include #include #include "Subleading.hh" #include "fastjet/ClusterSequence.hh" #include "HEJ/Constants.hh" #include "HEJ/EWConstants.hh" #include "HEJ/PDF.hh" #include "HEJ/PDG_codes.hh" #include "HEJ/Particle.hh" #include "HEJ/RNG.hh" #include "HEJ/exceptions.hh" #include "HEJ/kinematics.hh" #include "HEJ/utility.hh" #include "JetParameters.hh" #include "Process.hh" namespace HEJFOG { HEJ::Event::EventData to_EventData(PhaseSpacePoint psp){ //! @TODO Same function already in HEJ HEJ::Event::EventData result; result.incoming = std::move(psp).incoming_; // NOLINT(bugprone-use-after-move) result.outgoing = std::move(psp).outgoing_; // NOLINT(bugprone-use-after-move) // technically Event::EventData doesn't have to be sorted, // but PhaseSpacePoint should be anyway assert( std::is_sorted( begin(result.outgoing), end(result.outgoing), HEJ::rapidity_less{} ) ); assert(result.outgoing.size() >= 2); result.decays = std::move(psp).decays_; // NOLINT(bugprone-use-after-move) static_assert( std::numeric_limits::has_quiet_NaN, "no quiet NaN for double" ); constexpr double nan = std::numeric_limits::quiet_NaN(); result.parameters.central = {nan, nan, psp.weight()}; // NOLINT(bugprone-use-after-move) return result; } PhaseSpacePoint::ConstPartonIterator PhaseSpacePoint::begin_partons() const { return cbegin_partons(); } PhaseSpacePoint::ConstPartonIterator PhaseSpacePoint::cbegin_partons() const { return {HEJ::is_parton, cbegin(outgoing()), cend(outgoing())}; } PhaseSpacePoint::ConstPartonIterator PhaseSpacePoint::end_partons() const { return cend_partons(); } PhaseSpacePoint::ConstPartonIterator PhaseSpacePoint::cend_partons() const { return {HEJ::is_parton, cend(outgoing()), cend(outgoing())}; } PhaseSpacePoint::ConstReversePartonIterator PhaseSpacePoint::rbegin_partons() const { return crbegin_partons(); } PhaseSpacePoint::ConstReversePartonIterator PhaseSpacePoint::crbegin_partons() const { return std::reverse_iterator( cend_partons() ); } PhaseSpacePoint::ConstReversePartonIterator PhaseSpacePoint::rend_partons() const { return crend_partons(); } PhaseSpacePoint::ConstReversePartonIterator PhaseSpacePoint::crend_partons() const { return std::reverse_iterator( cbegin_partons() ); } PhaseSpacePoint::PartonIterator PhaseSpacePoint::begin_partons() { return {HEJ::is_parton, begin(outgoing_), end(outgoing_)}; } PhaseSpacePoint::PartonIterator PhaseSpacePoint::end_partons() { return {HEJ::is_parton, end(outgoing_), end(outgoing_)}; } PhaseSpacePoint::ReversePartonIterator PhaseSpacePoint::rbegin_partons() { return std::reverse_iterator( end_partons() ); } PhaseSpacePoint::ReversePartonIterator PhaseSpacePoint::rend_partons() { return std::reverse_iterator( begin_partons() ); } namespace { bool can_swap_to_uno( HEJ::Particle const & p1, HEJ::Particle const & p2 ){ assert(is_parton(p1) && is_parton(p2)); return p1.type != HEJ::pid::gluon && p2.type == HEJ::pid::gluon; } template bool uno_possible( PartonIt first_parton, OutIt first_out ){ using namespace HEJ; // Special case: Higgs can not be outside of uno if(first_out->type == pid::Higgs || std::next(first_out)->type==pid::Higgs){ return false; } // decide what kind of subleading process is allowed return can_swap_to_uno( *first_parton, *std::next(first_parton) ); } bool is_AWZ_proccess(Process const & proc){ return proc.boson && HEJ::is_AWZ_boson(*proc.boson); } bool is_up_type(HEJ::Particle const & part){ return is_anyquark(part) && ((std::abs(part.type)%2) == 0); } bool is_down_type(HEJ::Particle const & part){ return is_anyquark(part) && ((std::abs(part.type)%2) != 0); } bool can_couple_to_W( HEJ::Particle const & part, HEJ::pid::ParticleID const W_id ){ const int W_charge = W_id>0?1:-1; return std::abs(part.type) 0 && is_up_type(part)) || (W_charge*part.type < 0 && is_down_type(part)) ); } } // namespace namespace { template bool allow_strange( Iterator first_parton, Iterator last_parton, Process const & proc ) { const auto boson = proc.boson; return !( boson && std::abs(*boson)== HEJ::pid::Wp && std::none_of( first_parton, last_parton, [boson](HEJ::Particle const & p){ return can_couple_to_W(p, *boson); }) ); } } void PhaseSpacePoint::turn_to_subl( subleading::Channels const channel, Process const & proc, HEJ::RNG & ran ) { using namespace HEJ; assert(proc.njets > 2); switch(channel) { case subleading::unordered: { bool const can_be_uno_backward = uno_possible(cbegin_partons(), outgoing_.cbegin()); bool const can_be_uno_forward = uno_possible(crbegin_partons(), outgoing_.crbegin()); return turn_to_uno(can_be_uno_backward, can_be_uno_forward, ran); } case subleading::central_qqbar: { bool const strange_allowed = allow_strange( begin_partons(), end_partons(), proc ); return turn_to_cqqbar(strange_allowed, ran); } case subleading::extremal_qqbar: { bool const strange_allowed = allow_strange( begin_partons(), end_partons(), proc ); return turn_to_eqqbar(strange_allowed, ran); } default:; } throw std::logic_error{"enum value not covered"}; } void PhaseSpacePoint::turn_to_uno( const bool can_be_uno_backward, const bool can_be_uno_forward, HEJ::RNG & ran ){ if(can_be_uno_backward && can_be_uno_forward){ weight_ *= 2.; if(ran.flat() < 0.5){ return std::swap(begin_partons()->type, std::next(begin_partons())->type); } return std::swap(rbegin_partons()->type, std::next(rbegin_partons())->type); } if(can_be_uno_backward){ return std::swap(begin_partons()->type, std::next(begin_partons())->type); } assert(can_be_uno_forward); std::swap(rbegin_partons()->type, std::next(rbegin_partons())->type); } //! select flavour of quark HEJ::ParticleID PhaseSpacePoint::select_qqbar_flavour( const bool allow_strange, HEJ::RNG & ran ){ const double r1 = 2.*ran.flat()-1.; const double max_flavour = allow_strange?HEJ::N_F:HEJ::N_F-1; weight_ *= max_flavour*2; double const flavour = HEJ::pid::down + std::floor(std::abs(r1)*max_flavour); return static_cast(flavour*(r1<0.?-1:1)); } void PhaseSpacePoint::turn_to_cqqbar(const bool allow_strange, HEJ::RNG & ran){ // we assume all FKL partons to be gluons auto first = std::next(begin_partons()); auto last = std::next(rbegin_partons()); auto const ng = std::distance(first, last.base()); if(ng < 2) throw std::logic_error("not enough gluons to create qqbar"); auto flavour = select_qqbar_flavour(allow_strange, ran); // select gluon for switch if(ng!=2){ const double steps = 1./(ng-1.); weight_ /= steps; for(auto rnd = ran.flat(); rnd>steps; ++first){ rnd-=steps; } } first->type = flavour; std::next(first)->type = anti(flavour); } void PhaseSpacePoint::turn_to_eqqbar(const bool allow_strange, HEJ::RNG & ran){ /// find first and last gluon in FKL chain auto first = begin_partons(); const bool can_forward = !is_anyquark(*first); auto last = rbegin_partons(); const bool can_backward = !is_anyquark(*last); if(std::distance(first, last.base()) < 2) throw std::logic_error("not enough gluons to create qqbar"); auto flavour = select_qqbar_flavour(allow_strange, ran); // select gluon for switch if(can_forward && !can_backward){ first->type = flavour; std::next(first)->type = anti(flavour); return; } if(!can_forward && can_backward){ last->type = flavour; std::next(last)->type = anti(flavour); return; } assert(can_forward && can_backward); weight_*=2.; if(ran.flat()>0.5){ first->type = flavour; std::next(first)->type = anti(flavour); return; } last->type = flavour; std::next(last)->type = anti(flavour); } template fastjet::PseudoJet PhaseSpacePoint::gen_last_momentum( ParticleMomenta const & other_momenta, const double mass_square, const double y ) const { std::array pt{0.,0.}; for (auto const & p: other_momenta) { pt[0]-= p.px(); pt[1]-= p.py(); } const double mperp = std::sqrt(pt[0]*pt[0]+pt[1]*pt[1]+mass_square); const double pz=mperp*std::sinh(y); const double E=mperp*std::cosh(y); return {pt[0], pt[1], pz, E}; } Decay PhaseSpacePoint::select_decay_channel( std::vector const & decays, HEJ::RNG & ran ){ double br_total = 0.; for(auto const & decay: decays) br_total += decay.branching_ratio; // adjust weight // this is given by (channel branching ratio)/(chance to pick channel) // where (chance to pick channel) = // (channel branching ratio)/(total branching ratio) weight_ *= br_total; if(decays.size()==1) return decays.front(); const double r1 = br_total*ran.flat(); double br_sum = 0.; for(auto const & decay: decays){ br_sum += decay.branching_ratio; if(r1 < br_sum) return decay; } throw std::logic_error{"unreachable"}; } namespace { //! generate decay products of a boson std::vector decay_boson( HEJ::Particle const & parent, std::vector const & decays, HEJ::RNG & ran ){ if(decays.size() != 2){ throw HEJ::not_implemented{ "only decays into two particles are implemented" }; } std::vector decay_products(decays.size()); for(size_t i = 0; i < decays.size(); ++i){ decay_products[i].type = decays[i]; } // choose polar and azimuth angle in parent rest frame const double E = parent.m()/2; const double theta = 2.*M_PI*ran.flat(); const double cos_phi = 2.*ran.flat()-1.; // Jacobian Factors for W in line 418 const double sin_phi = std::sqrt(1. - cos_phi*cos_phi); // Know 0 < phi < pi const double px = E*std::cos(theta)*sin_phi; const double py = E*std::sin(theta)*sin_phi; const double pz = E*cos_phi; decay_products[0].p.reset(px, py, pz, E); decay_products[1].p.reset(-px, -py, -pz, E); for(auto & particle: decay_products) particle.p.boost(parent.p); return decay_products; } } // namespace std::vector PhaseSpacePoint::decay_channel( HEJ::Particle const & parent, std::vector const & decays, HEJ::RNG & ran ){ const auto channel = select_decay_channel(decays, ran); return decay_boson(parent, channel.products, ran); } namespace { //! adds a particle to target (in correct rapidity ordering) //! @returns positon of insertion auto insert_particle(std::vector & target, HEJ::Particle && particle ){ const auto pos = std::upper_bound( begin(target),end(target),particle,HEJ::rapidity_less{} ); target.insert(pos, std::move(particle)); return pos; } } // namespace PhaseSpacePoint::PhaseSpacePoint( Process const & proc, JetParameters const & jet_param, HEJ::PDF & pdf, double E_beam, double const subl_chance, Subleading const subl_channels, ParticlesDecayMap const & particle_decays, HEJ::EWConstants const & ew_parameters, HEJ::RNG & ran ){ assert(proc.njets >= 2); status_ = Status::good; weight_ = 1; // ensure that all setting are consistent // a more thorough check is in EventGenerator assert(subl_chance > 0. || subl_channels.none()); const std::size_t nout = proc.njets + (proc.boson?1:0) + proc.boson_decay.size(); outgoing_.reserve(nout); // generate parton momenta const bool is_pure_jets = (nout == proc.njets); auto partons = gen_LO_partons( proc.njets, is_pure_jets, jet_param, E_beam, ran ); if(status_ != Status::good) return; // pre fill flavour with gluons for(auto && parton: std::move(partons)){ outgoing_.emplace_back(HEJ::Particle{HEJ::pid::gluon, std::move(parton), {}}); } const std::optional channel = select_channel( subl_channels, subl_chance, ran ); - if(proc.boson){ // decay boson - auto const & boson_prop = (*proc.boson == HEJ::pid::Z_photon_mix - ? ew_parameters.prop(HEJ::pid::Z) - : ew_parameters.prop(*proc.boson)); - auto boson = gen_boson( - *proc.boson, boson_prop.mass, boson_prop.width, - proc, - channel, - ran - ); - const auto pos{insert_particle(outgoing_, std::move(boson))}; - const size_t boson_idx = std::distance(begin(outgoing_), pos); - auto const & boson_decay = particle_decays.find(*proc.boson); - if( !proc.boson_decay.empty() ){ // decay given in proc - decays_.emplace( - boson_idx, - decay_boson(outgoing_[boson_idx], proc.boson_decay, ran) - ); - } else if( boson_decay != particle_decays.end() - && !boson_decay->second.empty() ){ // decay given explicitly - decays_.emplace( - boson_idx, - decay_channel(outgoing_[boson_idx], boson_decay->second, ran) - ); - } + if(proc.boson) { + add_boson(proc, channel, particle_decays, ew_parameters, ran); } // normalisation of momentum-conserving delta function weight_ *= std::pow(2*M_PI, 4); /** @TODO * uf (jet_param.min_pt) doesn't correspond to our final scale choice. * The HEJ scale generators currently expect a full event as input, * so fixing this is not completely trivial */ reconstruct_incoming(proc, channel, pdf, E_beam, jet_param.min_pt, ran); if(status_ != Status::good) return; // set outgoing states begin_partons()->type = incoming_[0].type; rbegin_partons()->type = incoming_[1].type; if(channel) turn_to_subl(*channel, proc, ran); if(proc.boson) couple_boson(*proc.boson, ran); } + void PhaseSpacePoint::add_boson( + Process const & proc, + std::optional const channel, + ParticlesDecayMap const & particle_decays, + HEJ::EWConstants const & ew_parameters, + HEJ::RNG & ran + ) { + auto const & boson_prop = (*proc.boson == HEJ::pid::Z_photon_mix + ? ew_parameters.prop(HEJ::pid::Z) + : ew_parameters.prop(*proc.boson)); + auto boson = gen_boson( + *proc.boson, boson_prop.mass, boson_prop.width, + proc, + channel, + ran + ); + const auto pos{insert_particle(outgoing_, std::move(boson))}; + const size_t boson_idx = std::distance(begin(outgoing_), pos); + auto const & boson_decay = particle_decays.find(*proc.boson); + if( !proc.boson_decay.empty() ){ // decay given in proc + decays_.emplace( + boson_idx, + decay_boson(outgoing_[boson_idx], proc.boson_decay, ran) + ); + } else if( boson_decay != particle_decays.end() + && !boson_decay->second.empty() ){ // decay given explicitly + decays_.emplace( + boson_idx, + decay_channel(outgoing_[boson_idx], boson_decay->second, ran) + ); + } + } + // pt generation, see eq:pt_sampling in developer manual double PhaseSpacePoint::gen_hard_pt( const int np , const double ptmin, const double ptmax, const double /* y */, HEJ::RNG & ran ){ // heuristic parameter for pt sampling, see eq:pt_par in developer manual const double ptpar = ptmin + np/5.; const double arctan = std::atan((ptmax - ptmin)/ptpar); const double xpt = ran.flat(); const double pt = ptmin + ptpar*std::tan(xpt*arctan); const double cosine = std::cos(xpt*arctan); weight_ *= pt*ptpar*arctan/(cosine*cosine); return pt; } double PhaseSpacePoint::gen_soft_pt(int np, double max_pt, HEJ::RNG & ran) { constexpr double ptpar = 4.; const double r = ran.flat(); const double pt = max_pt + ptpar/np*std::log(r); weight_ *= pt*ptpar/(np*r); return pt; } double PhaseSpacePoint::gen_parton_pt( int count, JetParameters const & jet_param, double max_pt, double y, HEJ::RNG & ran ) { constexpr double p_small_pt = 0.02; if(! jet_param.peak_pt) { return gen_hard_pt(count, jet_param.min_pt, max_pt, y, ran); } const double r = ran.flat(); if(r > p_small_pt) { weight_ /= 1. - p_small_pt; return gen_hard_pt(count, *jet_param.peak_pt, max_pt, y, ran); } weight_ /= p_small_pt; const double pt = gen_soft_pt(count, *jet_param.peak_pt, ran); if(pt < jet_param.min_pt) { weight_=0.0; status_ = Status::not_enough_jets; return jet_param.min_pt; } return pt; } std::vector PhaseSpacePoint::gen_LO_partons( int np, bool is_pure_jets, JetParameters const & jet_param, double max_pt, HEJ::RNG & ran ){ if (np<2) throw std::invalid_argument{"Not enough partons in gen_LO_partons"}; weight_ /= std::pow(16.*std::pow(M_PI,3),np); weight_ /= std::tgamma(np+1); //remove rapidity ordering std::vector partons; partons.reserve(np); for(int i = 0; i < np; ++i){ const double y = -jet_param.max_y + 2*jet_param.max_y*ran.flat(); weight_ *= 2*jet_param.max_y; const bool is_last_parton = i+1 == np; if(is_pure_jets && is_last_parton) { constexpr double parton_mass_sq = 0.; partons.emplace_back(gen_last_momentum(partons, parton_mass_sq, y)); break; } const double phi = 2*M_PI*ran.flat(); weight_ *= 2.0*M_PI; const double pt = gen_parton_pt(np, jet_param, max_pt, y, ran); if(weight_ == 0.0) return {}; partons.emplace_back(fastjet::PtYPhiM(pt, y, phi)); assert(jet_param.min_pt <= partons[i].pt()); assert(partons[i].pt() <= max_pt+1e-5); } // Need to check that at LO, the number of jets = number of partons; fastjet::ClusterSequence cs(partons, jet_param.def); auto cluster_jets=cs.inclusive_jets(jet_param.min_pt); if (cluster_jets.size()!=unsigned(np)){ weight_=0.0; status_ = Status::not_enough_jets; return {}; } std::sort(begin(partons), end(partons), HEJ::rapidity_less{}); return partons; } HEJ::Particle PhaseSpacePoint::gen_boson( HEJ::ParticleID bosonid, double mass, double width, Process const & proc, std::optional const channel, HEJ::RNG & ran ){ // Usual phase space measure for single particle, // see eq:single_particle_phase_space in developer manual weight_ /= 16.*std::pow(M_PI, 3); const double y = (bosonid == HEJ::pid::Higgs)? gen_Higgs_rapidity(proc, channel, ran): gen_V_boson_rapidity(ran); // off-shell sampling, see eq:breit-wigner-sampling in developer manual const double r1 = ran.flat(); const double s_boson = mass*( mass + width*std::tan(M_PI/2.*r1 + (r1-1.)*std::atan(mass/width)) ); if(bosonid != HEJ::pid::Higgs){ // two-particle phase space, // compare eq:two_particle_phase_space and eq:one_particle_phase_space // in developer manual weight_/=M_PI*M_PI*16.; // Jacobian, see eq:breit-wigner-sampling_jacobian in developer manual weight_*= mass*width*( M_PI+2.*std::atan(mass/width) ) / ( 1. + std::cos( M_PI*r1 + 2.*(r1-1.)*std::atan(mass/width) ) ); } return { bosonid, gen_last_momentum(outgoing_, s_boson, y), {} }; } double PhaseSpacePoint::gen_Higgs_rapidity( Process const & proc, std::optional const channel, HEJ::RNG & ran ) { constexpr double STDDEV_Y_H = 1.6; if(channel && *channel == subleading::uno) { assert(outgoing().size() >= 3); if(proc.incoming[0] == HEJ::pid::gluon) { // backward uno not possible // Higgs has to be before the second most forward parton assert(proc.incoming[1] != HEJ::pid::gluon); return random_normal_trunc( STDDEV_Y_H, ran, std::numeric_limits::lowest(), outgoing_[outgoing().size() - 2].rapidity() ); } if(proc.incoming[1] == HEJ::pid::gluon) { // forward uno not possible // Higgs has to be after the second most backward parton assert(proc.incoming[0] != HEJ::pid::gluon); return random_normal_trunc( STDDEV_Y_H, ran, outgoing_[1].rapidity(), std::numeric_limits::max() ); } } return random_normal(STDDEV_Y_H, ran); } double PhaseSpacePoint::gen_V_boson_rapidity( HEJ::RNG & ran ){ // two Gaussians around (+/-)2.6 of std width ~1.8 const int backward = int (2*ran.flat()); //0:forward 1:backward // This is not an integral over two distributions, but a random choice of // which option to take, each one representing the full integral. // So the weight of the integral should not be multiplied by 2 constexpr double STDDEV_Y_V = 1.8; const double y = random_normal(STDDEV_Y_V, ran); return y + (1.-2.*backward)*2.6; // add or subtract 2.6 } namespace { /// partons are ordered: even = anti, 0 = gluon constexpr HEJ::ParticleID index_to_pid(size_t i){ if(!i) return HEJ::pid::gluon; return static_cast( i%2 ? (i+1)/2 : -i/2 ); } /// partons are ordered: even = anti, 0 = gluon constexpr size_t pid_to_index(HEJ::ParticleID id){ if(id==HEJ::pid::gluon) return 0; return id>0 ? id*2-1 : std::abs(id)*2; } constexpr PhaseSpacePoint::part_mask GLUON = 1u << pid_to_index(HEJ::pid::gluon); constexpr PhaseSpacePoint::part_mask ALL = ~0; PhaseSpacePoint::part_mask init_allowed(HEJ::ParticleID const id){ if(std::abs(id) == HEJ::pid::proton) return ALL; PhaseSpacePoint::part_mask out{0}; if(HEJ::is_parton(id)) out[pid_to_index(id)] = true; return out; } /// decides which "index" (see index_to_pid) are allowed for process PhaseSpacePoint::part_mask allowed_quarks(HEJ::ParticleID const boson){ if(std::abs(boson) != HEJ::pid::Wp){ return ~GLUON; } // special case W: // Wp: anti-down or up-type quark, no b/t // Wm: down or anti-up-type quark, no b/t return boson>0?0b00011001100 // NOLINT(readability-magic-numbers) :0b00100110010; // NOLINT(readability-magic-numbers) } } // namespace std::array PhaseSpacePoint::incoming_AWZ( Process const & proc, std::array allowed_partons, HEJ::RNG & ran ){ assert(proc.boson); auto couple_parton = allowed_quarks(*proc.boson); if( // coupling possible through input allowed_partons[0] == (couple_parton&allowed_partons[0]) || allowed_partons[1] == (couple_parton&allowed_partons[1]) ){ return allowed_partons; } // only first can couple if( (allowed_partons[0]&couple_parton).any() &&(allowed_partons[1]&couple_parton).none() ){ return {allowed_partons[0]&couple_parton, allowed_partons[1]}; } // only second can couple if( (allowed_partons[0]&couple_parton).none() && (allowed_partons[1]&couple_parton).any() ){ return {allowed_partons[0], allowed_partons[1]&couple_parton}; } // both can couple if( (allowed_partons[0]&couple_parton).any() && (allowed_partons[1]&couple_parton).any() ){ double rnd = ran.flat(); weight_*=3.; if(rnd<1./3.){ return { allowed_partons[0] & couple_parton, allowed_partons[1] & ~couple_parton }; } if(rnd<2./3.){ return { allowed_partons[0] & ~couple_parton, allowed_partons[1] & couple_parton }; } return { allowed_partons[0] & couple_parton, allowed_partons[1] & couple_parton }; } throw std::invalid_argument{"Incoming state not allowed."}; } std::array PhaseSpacePoint::incoming_eqqbar( std::array allowed_partons, HEJ::RNG & ran ){ auto const gluon_idx = pid_to_index(HEJ::pid::gluon); auto & first_beam = allowed_partons[0]; auto & second_beam = allowed_partons[1]; if(first_beam[gluon_idx] && !second_beam[gluon_idx]){ first_beam.reset(); first_beam.set(gluon_idx); return allowed_partons; } if(!first_beam[gluon_idx] && second_beam[gluon_idx]) { second_beam.reset(); second_beam.set(gluon_idx); return allowed_partons; } if(first_beam[gluon_idx] && second_beam[gluon_idx]) { // both beams can be gluons // if one can't be a quark everything is good auto first_quarks = first_beam; first_quarks.reset(gluon_idx); auto second_quarks = second_beam; second_quarks.reset(gluon_idx); if(first_quarks.none() || second_quarks.none()){ return allowed_partons; } // else choose one to be a gluon double rnd = ran.flat(); weight_*=3.; if(rnd<1./3.){ allowed_partons[0].reset(); allowed_partons[0].set(gluon_idx); allowed_partons[1].reset(gluon_idx); } else if(rnd<2./3.){ allowed_partons[1].reset(); allowed_partons[1].set(gluon_idx); allowed_partons[0].reset(gluon_idx); } else { allowed_partons[0].reset(); allowed_partons[0].set(gluon_idx); allowed_partons[1].reset(); allowed_partons[1].set(gluon_idx); } return allowed_partons; } throw std::invalid_argument{ "Incoming state not allowed for pure extremal qqbar."}; } std::array PhaseSpacePoint::incoming_uno( std::array allowed_partons, HEJ::RNG & ran ){ auto const gluon_idx = pid_to_index(HEJ::pid::gluon); auto & first_beam = allowed_partons[0]; auto & second_beam = allowed_partons[1]; // cannot have Higgs on same side as uno if(outgoing_[0].type == HEJ::pid::Higgs || outgoing_[1].type == HEJ::pid::Higgs) { assert(outgoing().size() >= 4); second_beam.reset(gluon_idx); assert(second_beam.any()); } else if( outgoing_.back().type == HEJ::pid::Higgs || outgoing_[outgoing_.size() - 2].type == HEJ::pid::Higgs ) { assert(outgoing().size() >= 4); first_beam.reset(gluon_idx); assert(first_beam.any()); } auto first_quarks = first_beam; first_quarks.reset(gluon_idx); auto second_quarks = second_beam; second_quarks.reset(gluon_idx); if(first_quarks.any() && second_quarks.none()){ first_beam.reset(gluon_idx); return allowed_partons; } if(first_quarks.none() && second_quarks.any()) { second_beam.reset(gluon_idx); return allowed_partons; } if(first_quarks.any() && second_quarks.any()) { // both beams can be quarks // if one can't be gluon everything is good if(!first_beam[gluon_idx] || !second_beam[gluon_idx]){ return allowed_partons; } // else choose one to be a quark double rnd = ran.flat(); weight_*=3.; if(rnd<1./3.){ allowed_partons[0].reset(gluon_idx); allowed_partons[1].reset(); allowed_partons[1].set(gluon_idx); } else if(rnd<2./3.){ allowed_partons[1].reset(gluon_idx); allowed_partons[0].reset(); allowed_partons[0].set(gluon_idx); } else { allowed_partons[0].reset(gluon_idx); allowed_partons[1].reset(gluon_idx); } return allowed_partons; } throw std::invalid_argument{ "Incoming state not allowed for pure unordered."}; } /** * @brief Returns list of all allowed initial states partons * * checks which partons are allowed as initial state: * 1. only allow what is given in the Runcard (p -> all) * 2. A/W/Z require something to couple to * a) no qqbar => no incoming gluon * b) 2j => no incoming gluon * c) >3j => can couple OR is gluon => 2 gluons become qqbar later * 3. pure eqqbar requires at least one gluon * 4. pure uno requires at least one quark */ std::array PhaseSpacePoint::allowed_incoming( Process const & proc, std::optional channel, HEJ::RNG & ran ){ // all possible incoming states std::array allowed_partons{ init_allowed(proc.incoming[0]), init_allowed(proc.incoming[1]) }; // special case: A/W/Z without qqbar if( is_AWZ_proccess(proc) && (!channel || *channel == subleading::unordered) ) { return incoming_AWZ(proc, allowed_partons, ran); } if(!channel) return allowed_partons; switch(*channel) { case subleading::central_qqbar: return allowed_partons; case subleading::extremal_qqbar: return incoming_eqqbar(allowed_partons, ran); case subleading::unordered: return incoming_uno(allowed_partons, ran); default:; }; throw std::logic_error{"enum value not covered"}; } void PhaseSpacePoint::reconstruct_incoming( Process const & proc, std::optional const channel, HEJ::PDF & pdf, double E_beam, double uf, HEJ::RNG & ran ){ std::tie(incoming_[0].p, incoming_[1].p) = incoming_momenta(outgoing_); // calculate xa, xb const double sqrts=2*E_beam; const double xa=(incoming_[0].E()-incoming_[0].pz())/sqrts; const double xb=(incoming_[1].E()+incoming_[1].pz())/sqrts; // abort if phase space point is outside of collider energy reach if (xa>1. || xb>1.){ weight_=0; status_ = Status::too_much_energy; return; } auto const & ids = proc.incoming; std::array allowed_partons = allowed_incoming(proc, channel, ran); for(size_t i = 0; i < 2; ++i){ if(ids[i] == HEJ::pid::proton || ids[i] == HEJ::pid::p_bar){ // pick ids according to pdfs incoming_[i].type = generate_incoming_id(i, i?xb:xa, uf, pdf, allowed_partons[i], ran); } else { assert(allowed_partons[i][pid_to_index(ids[i])]); incoming_[i].type = ids[i]; } } assert(momentum_conserved(1e-7)); } HEJ::ParticleID PhaseSpacePoint::generate_incoming_id( size_t const beam_idx, double const x, double const uf, HEJ::PDF & pdf, part_mask allowed_partons, HEJ::RNG & ran ){ std::array pdf_wt{}; pdf_wt[0] = allowed_partons[0]? std::fabs(pdf.pdfpt(beam_idx,x,uf,HEJ::pid::gluon)):0.; double pdftot = pdf_wt[0]; for(size_t i = 1; i < pdf_wt.size(); ++i){ pdf_wt[i] = allowed_partons[i]? 4./9.*std::fabs(pdf.pdfpt(beam_idx,x,uf,index_to_pid(i))):0; pdftot += pdf_wt[i]; } const double r1 = pdftot * ran.flat(); double sum = 0; for(size_t i=0; i < pdf_wt.size(); ++i){ if (r1 < (sum+=pdf_wt[i])){ weight_*= pdftot/pdf_wt[i]; return index_to_pid(i); } } std::cerr << "Error in choosing incoming parton: "< allowed_parts; for(auto part_it=begin_partons(); part_it!=end_partons(); ++part_it){ // Wp -> up OR anti-down, Wm -> anti-up OR down, no bottom if ( can_couple_to_W(*part_it, boson) ) allowed_parts.push_back(part_it); } if(allowed_parts.empty()){ throw std::logic_error{"Found no parton for coupling with boson"}; } // select one and flip it size_t idx = 0; if(allowed_parts.size() > 1){ /// @TODO more efficient sampling /// old code: probability[i] = exp(parton[i].y - W.y) idx = std::floor(ran.flat()*allowed_parts.size()); weight_ *= allowed_parts.size(); } const int W_charge = boson>0?1:-1; allowed_parts[idx]->type = static_cast( allowed_parts[idx]->type - W_charge ); } double PhaseSpacePoint::random_normal( double stddev, HEJ::RNG & ran ){ const double r1 = ran.flat(); const double r2 = ran.flat(); const double lninvr1 = -std::log(r1); const double result = stddev*std::sqrt(2.*lninvr1)*std::cos(2.*M_PI*r2); weight_ *= exp(result*result/(2*stddev*stddev))*std::sqrt(2.*M_PI)*stddev; return result; } double PhaseSpacePoint::random_normal_trunc( const double stddev, HEJ::RNG & ran, const double min, const double max ) { double result; std::uint64_t trials = 0; do { ++trials; const double r1 = ran.flat(); const double r2 = ran.flat(); const double lninvr1 = -std::log(r1); result = stddev*std::sqrt(2.*lninvr1)*std::cos(2.*M_PI*r2); } while(result < min || result > max); weight_ *= exp(result*result/(2*stddev*stddev))*std::sqrt(2.*M_PI)*stddev / trials; return result; } bool PhaseSpacePoint::momentum_conserved(double ep) const{ fastjet::PseudoJet diff; for(auto const & in: incoming()) diff += in.p; for(auto const & out: outgoing()) diff -= out.p; return HEJ::nearby_ep(diff, fastjet::PseudoJet{}, ep); } std::optional PhaseSpacePoint::select_channel( Subleading const subl_channels, double const chance, HEJ::RNG & ran ) { const double r = ran.flat(); if(r > chance) { weight_ /= 1 - chance; return {}; } // pick a random subleading channel (flat) const std::size_t num_channels = subl_channels.count(); weight_ *= num_channels / chance; std::size_t channel_idx = r / chance * num_channels; for( unsigned channel = subleading::first; channel <= subleading::last; ++channel ) { if(subl_channels.test(channel)) { if(channel_idx == 0) { return {static_cast(channel)}; } else { --channel_idx; } } } throw std::logic_error{"unreachable"}; } } // namespace HEJFOG