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diff --git a/FixedOrderGen/include/PhaseSpacePoint.hh b/FixedOrderGen/include/PhaseSpacePoint.hh
index 066e592..fe0266f 100644
--- a/FixedOrderGen/include/PhaseSpacePoint.hh
+++ b/FixedOrderGen/include/PhaseSpacePoint.hh
@@ -1,239 +1,231 @@
/** \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 <array>
#include <bitset>
#include <cstddef>
#include <unordered_map>
#include <vector>
#include "HEJ/Event.hh"
#include "HEJ/Particle.hh"
#include "HEJ/PDG_codes.hh"
#include "fastjet/PseudoJet.hh"
#include "Decay.hh"
#include "Status.hh"
#include "Subleading.hh"
namespace HEJ {
class EWConstants;
class PDF;
class RNG;
}
namespace HEJFOG {
class JetParameters;
class Process;
//! A point in resummation phase space
class PhaseSpacePoint{
public:
//! Default PhaseSpacePoint Constructor
PhaseSpacePoint() = delete;
//! PhaseSpacePoint Constructor
/**
* @param proc The process to generate
* @param jet_properties 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 change 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_properties,
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<HEJ::Particle, 2> const & incoming() const{
return incoming_;
}
//! Get Outgoing Function
/**
* @returns Outgoing Particles
*/
std::vector<HEJ::Particle> const & outgoing() const{
return outgoing_;
}
std::unordered_map<std::size_t, std::vector<HEJ::Particle>> const & decays() const{
return decays_;
}
private:
friend HEJ::Event::EventData to_EventData(PhaseSpacePoint psp);
/**
* @internal
* @brief Generate LO parton momentum
*
* @param count 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<fastjet::PseudoJet> gen_LO_partons(
int count, bool is_pure_jets,
JetParameters const & jet_param,
double max_pt,
HEJ::RNG & ran
);
HEJ::Particle gen_boson(
HEJ::ParticleID bosonid, double mass, double width,
HEJ::RNG & ran
);
template<class ParticleMomenta>
fastjet::PseudoJet gen_last_momentum(
ParticleMomenta const & other_momenta,
double mass_square, double y
) const;
bool jets_ok(
std::vector<fastjet::PseudoJet> const & Born_jets,
std::vector<fastjet::PseudoJet> 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, Subleading subl_channels,
HEJ::PDF & pdf, double E_beam,
double uf,
HEJ::RNG & ran
);
- /**
- * @internal
- * @brief Returns list of all allowed initial states partons
- */
- std::array<std::bitset<11>,2> filter_partons(
- Process const & proc, Subleading subl_channels,
- HEJ::RNG & ran
- );
HEJ::ParticleID generate_incoming_id(
std::size_t beam_idx, double x, double uf, HEJ::PDF & pdf,
std::bitset<11> allowed_partons, HEJ::RNG & ran
);
bool momentum_conserved(double ep) const;
HEJ::Particle const & most_backward_FKL(
std::vector<HEJ::Particle> const & partons
) const;
HEJ::Particle const & most_forward_FKL(
std::vector<HEJ::Particle> const & partons
) const;
HEJ::Particle & most_backward_FKL(std::vector<HEJ::Particle> & partons) const;
HEJ::Particle & most_forward_FKL(std::vector<HEJ::Particle> & partons) const;
bool extremal_FKL_ok(
std::vector<fastjet::PseudoJet> const & partons
) const;
double random_normal(double stddev, HEJ::RNG & ran);
/**
* @internal
* @brief Turns a FKL configuration into a subleading one
*
* @param chance Change 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 maybe_turn_to_subl(double chance, Subleading channels,
Process const & proc, HEJ::RNG & ran);
void turn_to_uno(bool can_be_uno_backward, bool can_be_uno_forward,
HEJ::RNG & ran);
void turn_to_qqx(bool allow_strange, HEJ::RNG & ran);
//! decay where we select the decay channel
std::vector<HEJ::Particle> decay_boson(
HEJ::Particle const & parent,
std::vector<Decay> const & decays,
HEJ::RNG & ran
);
//! generate decay products of a boson
std::vector<HEJ::Particle> decay_boson(
HEJ::Particle const & parent,
std::vector<HEJ::ParticleID> 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<Decay> 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 ptmax, HEJ::RNG & ran);
double gen_parton_pt(
int count, JetParameters const & jet_param, double ptmax, double y,
HEJ::RNG & ran
);
double weight_;
Status status_;
std::array<HEJ::Particle, 2> incoming_;
std::vector<HEJ::Particle> outgoing_;
//! Particle decays in the format {outgoing index, decay products}
std::unordered_map<std::size_t, std::vector<HEJ::Particle>> decays_;
};
//! Extract HEJ::Event::EventData from PhaseSpacePoint
HEJ::Event::EventData to_EventData(PhaseSpacePoint psp);
}
diff --git a/FixedOrderGen/src/PhaseSpacePoint.cc b/FixedOrderGen/src/PhaseSpacePoint.cc
index 4ef36e8..38831f1 100644
--- a/FixedOrderGen/src/PhaseSpacePoint.cc
+++ b/FixedOrderGen/src/PhaseSpacePoint.cc
@@ -1,730 +1,735 @@
/**
* \authors The HEJ collaboration (see AUTHORS for details)
* \date 2019-2020
* \copyright GPLv2 or later
*/
#include "PhaseSpacePoint.hh"
#include <algorithm>
#include <cassert>
#include <cmath>
#include <cstdlib>
#include <iostream>
#include <iterator>
#include <limits>
#include <tuple>
#include <type_traits>
#include <utility>
#include "fastjet/ClusterSequence.hh"
#include "HEJ/Constants.hh"
#include "HEJ/EWConstants.hh"
#include "HEJ/exceptions.hh"
#include "HEJ/kinematics.hh"
#include "HEJ/Particle.hh"
#include "HEJ/PDF.hh"
#include "HEJ/RNG.hh"
#include "HEJ/utility.hh"
#include "JetParameters.hh"
#include "Process.hh"
namespace {
using namespace HEJ;
static_assert(
std::numeric_limits<double>::has_quiet_NaN,
"no quiet NaN for double"
);
constexpr double NaN = std::numeric_limits<double>::quiet_NaN();
} // namespace anonymous
namespace HEJFOG {
Event::EventData to_EventData(PhaseSpacePoint psp){
//! @TODO Same function already in HEJ
Event::EventData result;
result.incoming = std::move(psp).incoming_;
assert(result.incoming.size() == 2);
result.outgoing = std::move(psp).outgoing_;
// technically Event::EventData doesn't have to be sorted,
// but PhaseSpacePoint should be anyway
assert(
std::is_sorted(
begin(result.outgoing), end(result.outgoing),
rapidity_less{}
)
);
assert(result.outgoing.size() >= 2);
result.decays = std::move(psp).decays_;
result.parameters.central = {NaN, NaN, psp.weight()};
return result;
}
namespace {
bool can_swap_to_uno(
Particle const & p1, Particle const & p2
){
return is_parton(p1)
&& p1.type != pid::gluon
&& p2.type == pid::gluon;
}
size_t count_gluons(std::vector<Particle>::const_iterator first,
std::vector<Particle>::const_iterator last
){
return std::count_if(first, last, [](Particle const & p)
{return p.type == pid::gluon;});
}
/** assumes FKL configurations between first and last,
* else there can be a quark in a non-extreme position
* e.g. uno configuration gqg would pass
*/
Subleading possible_qqx(
std::vector<Particle>::const_iterator first,
std::vector<Particle>::const_iterator last
){
using namespace subleading;
Subleading channels(~0l);
channels.reset(qqx);
channels.reset(eqqx);
channels.reset(cqqx);
auto const ngluon = count_gluons(first,last);
if(ngluon < 2) return channels;
return channels.set(qqx);
//! @TODO stub
if(ngluon == 2 && first->type==pid::gluon){
//! backwards qqx?
return channels.set(eqqx);
}
channels.set(cqqx);
return channels.set(eqqx);
}
bool is_AWZ_proccess(Process const & proc){
return proc.boson && is_AWZ_boson(*proc.boson);
}
bool is_up_type(Particle const & part){
return is_anyquark(part) && !(std::abs(part.type)%2);
}
bool is_down_type(Particle const & part){
return is_anyquark(part) && std::abs(part.type)%2;
}
bool can_couple_to_W(Particle const & part, pid::ParticleID const W_id){
const int W_charge = W_id>0?1:-1;
return std::abs(part.type)<5
&& ( (W_charge*part.type > 0 && is_up_type(part))
|| (W_charge*part.type < 0 && is_down_type(part)) );
}
}
void PhaseSpacePoint::maybe_turn_to_subl(
double chance,
Subleading channels,
Process const & proc,
RNG & ran
){
if(proc.njets <= 2) return;
assert(outgoing_.size() >= 2);
// decide what kind of subleading process is allowed
const size_t nout = outgoing_.size();
const bool can_be_uno_backward = can_swap_to_uno(outgoing_[0], outgoing_[1]);
const bool can_be_uno_forward = can_swap_to_uno(outgoing_[nout-1], outgoing_[nout-2]);
if(channels[subleading::uno]){
channels.set(subleading::uno, can_be_uno_backward || can_be_uno_forward);
}
channels &= possible_qqx(outgoing_.cbegin(), outgoing_.cend());
bool allow_strange = true;
if(is_AWZ_proccess(proc)) {
if(std::none_of(outgoing_.cbegin(), outgoing_.cend(),
[&proc](Particle const & p){
return can_couple_to_W(p, *proc.boson);})) {
// enforce qqx if A/W/Z can't couple somewhere else
// this is ensured to work through filter_partons in reconstruct_incoming
channels.reset(subleading::uno);
assert(channels.any());
chance = 1.;
// strange not allowed for W
if(std::abs(*proc.boson)== pid::Wp) allow_strange = false;
}
}
// no subleading
std::size_t const nchannels = channels.count();
if(nchannels==0) return;
if(ran.flat() >= chance){
weight_ /= 1 - chance;
return;
}
// select channel
weight_ /= chance;
double const step = 1./nchannels;
weight_*=nchannels;
unsigned selected = subleading::first;
double rnd = nchannels>1?ran.flat():0.;
for(; selected<=subleading::last; ++selected){
assert(rnd>=0);
if(channels[selected]){
if(rnd<step) break;
rnd-=step;
}
}
switch(selected){
case subleading::uno:
return turn_to_uno(can_be_uno_backward, can_be_uno_forward, ran);
case subleading::qqx:
case subleading::cqqx:
case subleading::eqqx:
return turn_to_qqx(allow_strange, ran);
default:
throw std::logic_error{"unreachable"};
}
}
void PhaseSpacePoint::turn_to_uno(
const bool can_be_uno_backward, const bool can_be_uno_forward,
RNG & ran
){
if(!can_be_uno_backward && !can_be_uno_forward) return;
const size_t nout = outgoing_.size();
if(can_be_uno_backward && can_be_uno_forward){
if(ran.flat() < 0.5){
std::swap(outgoing_[0].type, outgoing_[1].type);
} else {
std::swap(outgoing_[nout-1].type, outgoing_[nout-2].type);
}
weight_ *= 2.;
} else if(can_be_uno_backward){
std::swap(outgoing_[0].type, outgoing_[1].type);
} else {
assert(can_be_uno_forward);
std::swap(outgoing_[nout-1].type, outgoing_[nout-2].type);
}
}
void PhaseSpacePoint::turn_to_qqx(const bool allow_strange, RNG & ran){
/// find first and last gluon in FKL chain
auto first = std::find_if(outgoing_.begin(), outgoing_.end(),
[](Particle const & p){return p.type == pid::gluon;});
std::vector<Particle*> FKL_gluons;
for(auto p = first; p!=outgoing_.end(); ++p){
if(p->type == pid::gluon) FKL_gluons.push_back(&*p);
else if(is_anyquark(*p)) break;
}
const size_t ng = FKL_gluons.size();
if(ng < 2)
throw std::logic_error("not enough gluons to create qqx");
// select flavour of quark
const double r1 = 2.*ran.flat()-1.;
const double max_flavour = allow_strange?N_F:N_F-1;
weight_ *= max_flavour*2;
int flavour = pid::down + std::floor(std::abs(r1)*max_flavour);
flavour*=r1<0.?-1:1;
// select gluon for switch
const size_t idx = std::floor((ng-1) * ran.flat());
weight_ *= (ng-1);
FKL_gluons[idx]->type = ParticleID(flavour);
FKL_gluons[idx+1]->type = ParticleID(-flavour);
}
template<class ParticleMomenta>
fastjet::PseudoJet PhaseSpacePoint::gen_last_momentum(
ParticleMomenta const & other_momenta,
const double mass_square, const double y
) const {
std::array<double,2> 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};
}
namespace {
//! adds a particle to target (in correct rapidity ordering)
//! @returns positon of insertion
auto insert_particle(std::vector<Particle> & target,
Particle && particle
){
const auto pos = std::upper_bound(
begin(target),end(target),particle,rapidity_less{}
);
target.insert(pos, std::move(particle));
return pos;
}
}
PhaseSpacePoint::PhaseSpacePoint(
Process const & proc,
JetParameters const & jet_param,
PDF & pdf, double E_beam,
double const subl_chance,
Subleading const subl_channels,
ParticlesDecayMap const & particle_decays,
EWConstants const & ew_parameters,
RNG & ran
){
assert(proc.njets >= 2);
status_ = good;
weight_ = 1;
const int 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
);
// pre fill flavour with gluons
for(auto&& p_out: partons) {
outgoing_.emplace_back(Particle{pid::gluon, std::move(p_out), {}});
}
if(status_ != good) return;
if(proc.boson){ // decay boson
auto const & boson_prop = ew_parameters.prop(*proc.boson) ;
auto boson{ gen_boson(*proc.boson, boson_prop.mass, boson_prop.width, 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_boson(outgoing_[boson_idx], boson_decay->second, 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, subl_channels, pdf, E_beam, jet_param.min_pt, ran);
if(status_ != good) return;
// set outgoing states
most_backward_FKL(outgoing_).type = incoming_[0].type;
most_forward_FKL(outgoing_).type = incoming_[1].type;
maybe_turn_to_subl(subl_chance, subl_channels, proc, ran);
if(proc.boson) couple_boson(*proc.boson, 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 */,
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, 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,
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_ = not_enough_jets;
return jet_param.min_pt;
}
return pt;
}
std::vector<fastjet::PseudoJet> PhaseSpacePoint::gen_LO_partons(
int np, bool is_pure_jets,
JetParameters const & jet_param,
double max_pt,
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<fastjet::PseudoJet> 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_ = not_enough_jets;
return {};
}
std::sort(begin(partons), end(partons), rapidity_less{});
return partons;
}
Particle PhaseSpacePoint::gen_boson(
ParticleID bosonid, double mass, double width,
RNG & ran
){
// Usual phase space measure
weight_ /= 16.*std::pow(M_PI, 3);
// Generate a y Gaussian distributed around 0
/// @TODO check magic numbers for different boson Higgs
/// @TODO better sampling for W
const double stddev_y = 1.6;
const double y = random_normal(stddev_y, ran);
const double r1 = ran.flat();
const double s_boson = mass*(
mass + width*std::tan(M_PI/2.*r1 + (r1-1.)*std::atan(mass/width))
);
// off-shell s_boson sampling, compensates for Breit-Wigner
/// @TODO use a flag instead
if(std::abs(bosonid) == pid::Wp){
weight_/=M_PI*M_PI*16.; //Corrects B-W factors, see git issue 132
weight_*= mass*width*( M_PI+2.*std::atan(mass/width) )
/ ( 1. + std::cos( M_PI*r1 + 2.*(r1-1.)*std::atan(mass/width) ) );
}
auto p = gen_last_momentum(outgoing_, s_boson, y);
return Particle{bosonid, std::move(p), {}};
}
Particle const & PhaseSpacePoint::most_backward_FKL(
std::vector<Particle> const & partons
) const{
if(!is_parton(partons[0])) return partons[1];
return partons[0];
}
Particle const & PhaseSpacePoint::most_forward_FKL(
std::vector<Particle> const & partons
) const{
const size_t last_idx = partons.size() - 1;
if(!is_parton(partons[last_idx])) return partons[last_idx-1];
return partons[last_idx];
}
Particle & PhaseSpacePoint::most_backward_FKL(
std::vector<Particle> & partons
) const{
if(!is_parton(partons[0])) return partons[1];
return partons[0];
}
Particle & PhaseSpacePoint::most_forward_FKL(
std::vector<Particle> & partons
) const{
const size_t last_idx = partons.size() - 1;
if(!is_parton(partons[last_idx])) return partons[last_idx-1];
return partons[last_idx];
}
namespace {
/// partons are ordered: even = anti, 0 = gluon
ParticleID index_to_pid(size_t i){
if(!i) return pid::gluon;
return static_cast<ParticleID>( i%2 ? (i+1)/2 : -i/2 );
}
/// partons are ordered: even = anti, 0 = gluon
size_t pid_to_index(ParticleID id){
if(id==pid::gluon) return 0;
return id>0 ? id*2-1 : std::abs(id)*2;
}
- std::bitset<11> init_allowed(ParticleID const id){
+ using part_mask = std::bitset<11>; //!< Selection mask for partons
+
+ part_mask init_allowed(ParticleID const id){
if(std::abs(id) == pid::proton)
return ~0;
- std::bitset<11> out{0};
+ part_mask out{0};
if(is_parton(id))
out[pid_to_index(id)] = 1;
return out;
}
/// decides which "index" (see index_to_pid) are allowed for process
- std::bitset<11> allowed_quarks(ParticleID const boson){
- std::bitset<11> allowed = ~0;
+ part_mask allowed_quarks(ParticleID const boson){
+ part_mask allowed = ~0;
if(std::abs(boson) == pid::Wp){
// special case W:
// Wp: anti-down or up-type quark, no b/t
// Wm: down or anti-up-type quark, no b/t
allowed = boson>0? 0b00011001101
:0b00100110011;
}
return allowed;
}
- }
- /**
- * 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 qqx => no incoming gluon
- * b) 2j => no incoming gluon
- * c) 3j => can couple OR is gluon => 2 gluons become qqx later
- */
- std::array<std::bitset<11>,2> PhaseSpacePoint::filter_partons(
- Process const & proc, Subleading const subl_channels, RNG & ran
- ){
- std::array<std::bitset<11>,2> allowed_partons{
- init_allowed(proc.incoming[0]),
- init_allowed(proc.incoming[1])
- };
- bool const allow_qqx = subl_channels[subleading::qqx];
- // special case A/W/Z
- if(is_AWZ_proccess(proc) && ((proc.njets < 4) || !allow_qqx)){
- // all possible incoming states
- auto allowed = allowed_quarks(*proc.boson);
- if(proc.njets == 2 || !allow_qqx) allowed[0]=0;
-
- // possible states per leg
- std::array<std::bitset<11>,2> const maybe_partons{
- allowed_partons[0]&allowed, allowed_partons[1]&allowed};
-
- if(maybe_partons[0].any() && maybe_partons[1].any()){
- // two options to get allowed initial state => choose one at random
- const size_t idx = ran.flat() < 0.5;
- allowed_partons[idx] = maybe_partons[idx];
- // else choose the possible
- } else if(maybe_partons[0].any()) {
- allowed_partons[0] = maybe_partons[0];
- } else if(maybe_partons[1].any()) {
- allowed_partons[1] = maybe_partons[1];
- } else{
- throw std::invalid_argument{"Incoming state not allowed."};
+ /**
+ * @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 qqx => no incoming gluon
+ * b) 2j => no incoming gluon
+ * c) 3j => can couple OR is gluon => 2 gluons become qqx later
+ */
+ std::array<part_mask,2> filter_partons(
+ Process const & proc, Subleading const subl_channels, RNG & ran
+ ){
+ std::array<part_mask,2> allowed_partons{
+ init_allowed(proc.incoming[0]),
+ init_allowed(proc.incoming[1])
+ };
+ bool const allow_qqx = subl_channels[subleading::qqx];
+ // special case A/W/Z
+ if(is_AWZ_proccess(proc) && ((proc.njets < 4) || !allow_qqx)){
+ // all possible incoming states
+ auto allowed = allowed_quarks(*proc.boson);
+ if(proc.njets == 2 || !allow_qqx) allowed.reset(0);
+
+ // possible states per leg
+ std::array<part_mask,2> const maybe_partons{
+ allowed_partons[0]&allowed, allowed_partons[1]&allowed};
+
+ if(maybe_partons[0].any() && maybe_partons[1].any()){
+ // two options to get allowed initial state => choose one at random
+ const size_t idx = ran.flat() < 0.5;
+ allowed_partons[idx] = maybe_partons[idx];
+ // else choose the possible
+ } else if(maybe_partons[0].any()) {
+ allowed_partons[0] = maybe_partons[0];
+ } else if(maybe_partons[1].any()) {
+ allowed_partons[1] = maybe_partons[1];
+ } else{
+ throw std::invalid_argument{"Incoming state not allowed."};
+ }
}
+ return allowed_partons;
}
- return allowed_partons;
}
+
void PhaseSpacePoint::reconstruct_incoming(
Process const & proc, Subleading const subl_channels,
PDF & pdf, double E_beam,
double uf,
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_ = too_much_energy;
return;
}
auto const & ids = proc.incoming;
- std::array<std::bitset<11>,2> allowed_partons
+ std::array<part_mask,2> allowed_partons
= filter_partons(proc, subl_channels, ran);
for(size_t i = 0; i < 2; ++i){
if(ids[i] == pid::proton || ids[i] == 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));
}
ParticleID PhaseSpacePoint::generate_incoming_id(
size_t const beam_idx, double const x, double const uf,
- PDF & pdf, std::bitset<11> allowed_partons, RNG & ran
+ PDF & pdf, part_mask allowed_partons, RNG & ran
){
std::array<double,11> pdf_wt;
pdf_wt[0] = allowed_partons[0]?
std::fabs(pdf.pdfpt(beam_idx,x,uf,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: "<<x<<" "<<uf<<" "
<<sum<<" "<<pdftot<<" "<<r1<<std::endl;
throw std::logic_error{"Failed to choose parton flavour"};
}
void PhaseSpacePoint::couple_boson(
ParticleID const boson, RNG & ran
){
if(std::abs(boson) != pid::Wp) return; // only matters for W
/// @TODO this could be use to sanity check gamma and Z
// find all possible quarks
std::vector<Particle*> allowed_parts;
for(auto & part: outgoing_){
// Wp -> up OR anti-down, Wm -> anti-up OR down, no bottom
if ( can_couple_to_W(part, boson) )
allowed_parts.push_back(&part);
}
if(allowed_parts.size() == 0){
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<ParticleID>( allowed_parts[idx]->type - W_charge );
}
double PhaseSpacePoint::random_normal(
double stddev,
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;
}
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 nearby_ep(diff, fastjet::PseudoJet{}, ep);
}
Decay PhaseSpacePoint::select_decay_channel(
std::vector<Decay> const & decays,
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"};
}
std::vector<Particle> PhaseSpacePoint::decay_boson(
Particle const & parent,
std::vector<Decay> const & decays,
RNG & ran
){
const auto channel = select_decay_channel(decays, ran);
return decay_boson(parent, channel.products, ran);
}
std::vector<Particle> PhaseSpacePoint::decay_boson(
Particle const & parent,
std::vector<ParticleID> const & decays,
RNG & ran
){
if(decays.size() != 2){
throw not_implemented{
"only decays into two particles are implemented"
};
}
std::vector<Particle> 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;
}
}

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