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diff --git a/FixedOrderGen/include/PhaseSpacePoint.hh b/FixedOrderGen/include/PhaseSpacePoint.hh
index a090e92..65df4f5 100644
--- a/FixedOrderGen/include/PhaseSpacePoint.hh
+++ b/FixedOrderGen/include/PhaseSpacePoint.hh
@@ -1,149 +1,153 @@
/** \file PhaseSpacePoint.hh
* \brief Contains the PhaseSpacePoint Class
*/
#pragma once
#include <vector>
#include "fastjet/JetDefinition.hh"
#include "RHEJ/utility.hh"
#include "RHEJ/Event.hh"
#include "RHEJ/PDG_codes.hh"
#include "RHEJ/PDF.hh"
#include "RHEJ/RNG.hh"
#include "Status.hh"
#include "HiggsProperties.hh"
namespace HEJFOG{
class Process;
using RHEJ::Particle;
//! A point in resummation phase space
class PhaseSpacePoint{
public:
//! Default PhaseSpacePoint Constructor
PhaseSpacePoint() = default;
//! PhaseSpacePoint Constructor
/**
* @param proc The process to generate
* @param jet_def The Jet Definition Used
* @param jetptmin Minimum Jet Transverse Momentum
* @param rapmax Maximum parton rapidity
* @param pdf The pdf set (used for sampling)
* @param uno_chance Chance to turn a potentially unordered
* emission into an actual one
*
* Initially, only FKL phase space points are generated. If the most
* extremal emission in any direction is a quark or anti-quark and the
* next emission is a gluon, uno_chance is the chance to turn this into
* an unordered emission event by swapping the two flavours. At most one
* unordered emission will be generated in this way.
*/
PhaseSpacePoint(
Process const & proc,
fastjet::JetDefinition jet_def,double jetptmin, double rapmax,
RHEJ::PDF & pdf, double E_beam,
double uno_chance,
HiggsProperties const & higgs_properties,
RHEJ::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<Particle, 2> const & incoming() const{
return incoming_;
}
//! Get Outgoing Function
/**
* @returns Outgoing Particles
*/
std::vector<Particle> const & outgoing() const{
return outgoing_;
}
std::unordered_map<int, std::vector<Particle>> const & decays() const{
return decays_;
}
private:
std::vector<fastjet::PseudoJet> gen_LO_partons(
int count, double ptmin, double ptmax, double rapmax,
RHEJ::RNG & ran
);
Particle gen_boson(
RHEJ::ParticleID bosonid, double mass, double width,
RHEJ::RNG & ran
);
bool jets_ok(
std::vector<fastjet::PseudoJet> const & Born_jets,
std::vector<fastjet::PseudoJet> const & partons
) const;
void reconstruct_incoming(
std::array<RHEJ::ParticleID, 2> const & ids,
RHEJ::PDF & pdf, double E_beam,
RHEJ::RNG & ran
);
RHEJ::ParticleID generate_incoming_id(
double x, double uf, RHEJ::PDF & pdf,
RHEJ::RNG & ran
);
bool momentum_conserved(double ep) const;
RHEJ::Particle const & most_backward_FKL(
std::vector<RHEJ::Particle> const & partons
) const;
RHEJ::Particle const & most_forward_FKL(
std::vector<RHEJ::Particle> const & partons
) const;
RHEJ::Particle & most_backward_FKL(std::vector<RHEJ::Particle> & partons) const;
RHEJ::Particle & most_forward_FKL(std::vector<RHEJ::Particle> & partons) const;
bool extremal_FKL_ok(
std::vector<fastjet::PseudoJet> const & partons
) const;
double random_normal(double stddev, RHEJ::RNG & ran);
void maybe_turn_to_uno(double chance, RHEJ::RNG & ran);
std::vector<Particle> decay_boson(
RHEJ::Particle const & parent,
std::vector<Decay> const & decays,
RHEJ::RNG & ran
);
Decay select_decay_channel(
std::vector<Decay> const & decays,
RHEJ::RNG & ran
);
+ double gen_hard_pt(
+ int count, double ptmin, double ptmax, double y,
+ RHEJ::RNG & ran
+ );
double weight_;
Status status_;
double jetptmin_;
fastjet::JetDefinition jet_def_;
std::array<Particle, 2> incoming_;
std::vector<Particle> outgoing_;
//! Particle decays in the format {outgoing index, decay products}
std::unordered_map<int, std::vector<Particle>> decays_;
};
RHEJ::UnclusteredEvent to_UnclusteredEvent(PhaseSpacePoint const & psp);
}
diff --git a/FixedOrderGen/src/PhaseSpacePoint.cc b/FixedOrderGen/src/PhaseSpacePoint.cc
index f922cd4..25989a2 100644
--- a/FixedOrderGen/src/PhaseSpacePoint.cc
+++ b/FixedOrderGen/src/PhaseSpacePoint.cc
@@ -1,419 +1,427 @@
#include "PhaseSpacePoint.hh"
#include <random>
#include "RHEJ/kinematics.hh"
#include "RHEJ/utility.hh"
#include "RHEJ/exceptions.hh"
#include "Process.hh"
#include <CLHEP/Random/Randomize.h>
#include <CLHEP/Random/RanluxEngine.h>
using namespace RHEJ;
namespace HEJFOG{
static_assert(
std::numeric_limits<double>::has_quiet_NaN,
"no quiet NaN for double"
);
constexpr double NaN = std::numeric_limits<double>::quiet_NaN();
RHEJ::UnclusteredEvent to_UnclusteredEvent(PhaseSpacePoint const & psp){
RHEJ::UnclusteredEvent result;
result.incoming = psp.incoming();
std::sort(
begin(result.incoming), end(result.incoming),
[](Particle o1, Particle o2){return o1.p.pz()<o2.p.pz();}
);
assert(result.incoming.size() == 2);
result.outgoing = psp.outgoing();
assert(
std::is_sorted(
begin(result.outgoing), end(result.outgoing),
RHEJ::rapidity_less{}
)
);
assert(result.outgoing.size() >= 2);
result.decays = psp.decays();
result.central.mur = NaN;
result.central.muf = NaN;
result.central.weight = psp.weight();
return result;
}
namespace{
bool can_swap_to_uno(
RHEJ::Particle const & p1, RHEJ::Particle const & p2
){
return is_parton(p1)
&& p1.type != RHEJ::pid::gluon
&& p2.type == RHEJ::pid::gluon;
}
}
void PhaseSpacePoint::maybe_turn_to_uno(
double chance,
RHEJ::RNG & ran
){
assert(outgoing_.size() >= 2);
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(!can_be_uno_backward && !can_be_uno_forward) return;
if(ran.flat() < chance){
weight_ /= chance;
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);
}
}
else weight_ /= 1 - chance;
}
PhaseSpacePoint::PhaseSpacePoint(
Process const & proc,
fastjet::JetDefinition jet_def,double jetptmin, double rapmax,
RHEJ::PDF & pdf, double E_beam,
double uno_chance,
HiggsProperties const & h,
RHEJ::RNG & ran
):
jetptmin_{jetptmin},
jet_def_{jet_def}
{
assert(proc.njets >= 2);
const int nout = proc.njets + (proc.boson?1:0);
status_ = good;
weight_ = 1;
weight_ /= std::tgamma(nout);
outgoing_.reserve(nout);
for(auto&& p_out: gen_LO_partons(proc.njets, jetptmin_, E_beam, rapmax, ran)){
outgoing_.emplace_back(Particle{pid::gluon, std::move(p_out)});
}
if(status_ != good) return;
if(proc.boson && *proc.boson == pid::Higgs){
// The Higgs
auto Hparticle=gen_boson(pid::higgs, h.mass, h.width, ran);
auto pos=std::upper_bound(
begin(outgoing_),end(outgoing_),Hparticle,rapidity_less{}
);
outgoing_.insert(pos, Hparticle);
if(! h.decays.empty()){
const int boson_idx = std::distance(begin(outgoing_), pos);
decays_.emplace(
boson_idx,
decay_boson(outgoing_[boson_idx], h.decays, ran)
);
}
}
reconstruct_incoming(proc.incoming, pdf, E_beam, ran);
if(status_ != good) return;
// set outgoing states
most_backward_FKL(outgoing_).type = incoming_[0].type;
most_forward_FKL(outgoing_).type = incoming_[1].type;
if(proc.njets > 2) maybe_turn_to_uno(uno_chance, ran);
}
- std::vector<fastjet::PseudoJet> PhaseSpacePoint::gen_LO_partons(
- int np , double ptmin, double ptmax, double rapmax,
+ double PhaseSpacePoint::gen_hard_pt(
+ int np , double ptmin, double ptmax, double y,
RHEJ::RNG & ran
- ){
- if (np<2) throw std::invalid_argument{"Not enough partons in gen_LO_partons"};
+ ) {
// heuristic parameters for pt sampling
const double ptpar = ptmin + np/5.;
const double arg_small_y = atan((ptmax - ptmin)/ptpar);
const double y_cut = 3.;
+ const double r1 = ran.flat();
+ if(y < y_cut){
+ const double pt = ptmin + ptpar*tan(r1*arg_small_y);
+ const double temp = cos(r1*arg_small_y);
+ weight_ *= pt*ptpar*arg_small_y/(temp*temp);
+ return pt;
+ }
+
+ const double ptpar2 = ptpar/(1 + 5*(y-y_cut));
+ const double temp = 1. - std::exp((ptmin-ptmax)/ptpar2);
+ const double pt = ptmin - ptpar2*std::log(1-r1*temp);
+ weight_ *= pt*ptpar2*temp/(1-r1*temp);
+ return pt;
+ }
+
+ std::vector<fastjet::PseudoJet> PhaseSpacePoint::gen_LO_partons(
+ int np , double ptmin, double ptmax, double rapmax,
+ RHEJ::RNG & ran
+ ){
+ if (np<2) throw std::invalid_argument{"Not enough partons in gen_LO_partons"};
+
weight_ /= pow(16.*pow(M_PI,3),np-2);
std::vector<fastjet::PseudoJet> partons;
partons.reserve(np);
for(int i = 0; i < np; ++i){
const double y = -rapmax + 2*rapmax*ran.flat();
weight_ *= 2*rapmax;
const double phi = 2*M_PI*ran.flat();
weight_ *= 2.0*M_PI;
- double pt;
- const double r1 = ran.flat();
- if(y < y_cut){
- pt = ptmin + ptpar*tan(r1*arg_small_y);
- const double temp = cos(r1*arg_small_y);
- weight_ *= pt*ptpar*arg_small_y/(temp*temp);
- }
- else{
- const double ptpar2 = ptpar/(1 + 5*(y-y_cut));
- const double temp = 1. - std::exp((ptmin-ptmax)/ptpar2);
- pt = ptmin - ptpar2*std::log(1-r1*temp);
- weight_ *= pt*ptpar2*temp/(1-r1*temp);
- }
+ const double pt = gen_hard_pt(np, ptmin, ptmax, y, ran);
partons.emplace_back(fastjet::PtYPhiM(pt, y, phi));
assert(ptmin-1e-5 <= partons[i].pt() && partons[i].pt() <= ptmax+1e-5);
}
// Need to check that at LO, the number of jets = number of partons;
fastjet::ClusterSequence cs(partons, jet_def_);
auto cluster_jets=cs.inclusive_jets(jetptmin_);
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(
RHEJ::ParticleID bosonid, double mass, double width,
RHEJ::RNG & ran
){
std::array<double,2> ptrans{0.,0.};
for (auto const & parton:outgoing_) {
ptrans[0]-=parton.px();
ptrans[1]-=parton.py();
}
// The Higgs:
// Generate a y Gaussian distributed around 0
const double y = random_normal(1.6, ran);
const double r1 = ran.flat();
const double sH = mass*(
mass + width*tan(M_PI/2.*r1 + (r1-1.)*atan(mass/width))
);
const double mHperp=sqrt(ptrans[0]*ptrans[0]+ptrans[1]*ptrans[1]+sH);
const double pz=mHperp*sinh(y);
const double E=mHperp*cosh(y);
return Particle{bosonid,fastjet::PseudoJet{ptrans[0],ptrans[1],pz,E}};
}
Particle const & PhaseSpacePoint::most_backward_FKL(
std::vector<Particle> const & partons
) const{
if(!RHEJ::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(!RHEJ::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(!RHEJ::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(!RHEJ::is_parton(partons[last_idx])) return partons[last_idx-1];
return partons[last_idx];
}
void PhaseSpacePoint::reconstruct_incoming(
std::array<RHEJ::ParticleID, 2> const & ids,
RHEJ::PDF & pdf, double E_beam,
RHEJ::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].p.e()-incoming_[0].p.pz())/sqrts;
const double xb=(incoming_[1].p.e()+incoming_[1].p.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;
}
// pick pdfs
/** TODO:
* ufa, ufb don't correspond to our final scale choice.
* The reversed HEJ scale generators currently expect a full event as input,
* so fixing this is not completely trivial
*/
if(ids[0] == pid::proton || ids[0] == pid::p_bar){
const double ufa=jetptmin_;
incoming_[0].type = generate_incoming_id(xa, ufa, pdf, ran);
}
else {
incoming_[0].type = ids[0];
}
if(ids[1] == pid::proton || ids[1] == pid::p_bar){
const double ufb=jetptmin_;
incoming_[1].type = generate_incoming_id(xb, ufb, pdf, ran);
}
else {
incoming_[1].type = ids[1];
}
assert(momentum_conserved(1e-7));
}
RHEJ::ParticleID PhaseSpacePoint::generate_incoming_id(
double x, double uf, RHEJ::PDF & pdf,
RHEJ::RNG & ran
){
const double pdfg=fabs(pdf.pdfpt(0,x,uf,pid::gluon));
const double pdfu=fabs(pdf.pdfpt(0,x,uf,pid::up));
const double pdfd=fabs(pdf.pdfpt(0,x,uf,pid::down));
const double pdfux=fabs(pdf.pdfpt(0,x,uf,pid::u_bar));
const double pdfdx=fabs(pdf.pdfpt(0,x,uf,pid::d_bar));
const double pdfc=fabs(pdf.pdfpt(0,x,uf,pid::charm));
const double pdfs=fabs(pdf.pdfpt(0,x,uf,pid::strange));
const double pdfsx=fabs(pdf.pdfpt(0,x,uf,pid::s_bar));
const double pdfb=fabs(pdf.pdfpt(0,x,uf,pid::b));
const double pdftot=pdfg+4.0/9.0*(pdfu + pdfd + pdfux + pdfdx +pdfs +pdfsx + 2.0*(pdfc +pdfb ));
const double r1=pdftot*ran.flat();
double sum;
if (r1<(sum=pdfg)) {
weight_*=pdftot/pdfg;
return pid::gluon;
}
if (r1<(sum+=(4./9.)*pdfu)) {
weight_*=pdftot/((4./9.)*pdfu);
return pid::up;
}
else if (r1<(sum+=(4./9.)*pdfd)) {
weight_*=pdftot/((4./9.)*pdfd);
return pid::down;
}
else if (r1<(sum+=(4./9.)*pdfux)) {
weight_*=pdftot/((4./9.)*pdfux);
return pid::u_bar;
}
else if (r1<(sum+=(4./9.)*pdfdx)) {
weight_*=pdftot/((4./9.)*pdfdx);
return pid::d_bar;
}
else if (r1<(sum+=(4./9.)*pdfc)) {
weight_*=pdftot/((4./9.)*pdfc);
return pid::c;
}
else if (r1<(sum+=(4./9.)*pdfc)){
weight_*=pdftot/((4./9.)*pdfc);
return pid::c_bar;
}
else if (r1<(sum+=(4./9.)*pdfs)) {
weight_*=pdftot/((4./9.)*pdfs);
return pid::s;
}
else if (r1<(sum+=(4./9.)*pdfsx)) {
weight_*=pdftot/((4./9.)*pdfsx);
return pid::s_bar;
}
else if (r1<(sum+=(4./9.)*pdfb)) {
weight_*=pdftot/((4./9.)*pdfb);
return pid::b;
}
else if (r1<=(sum+=(4./9.)*pdfb)) {
weight_*=pdftot/((4./9.)*pdfb);
return pid::b_bar;
}
std::cout << "Error in choosing incoming parton: "<<x<<" "<<uf<<" "<<sum<<" "<<pdftot<<" "<<r1;
std::cout << " "<<pdfg+4./9.*(pdfu+pdfux+pdfd+pdfdx+pdfs+pdfsx+2.*(pdfc+pdfb))<<std::endl;
throw std::logic_error{"Failed to choose parton flavour"};
}
double PhaseSpacePoint::random_normal(
double stddev,
RHEJ::RNG & ran
){
const double r1 = ran.flat();
const double r2 = ran.flat();
const double lninvr1 = -log(r1);
const double result = stddev*sqrt(2.*lninvr1)*cos(2.*M_PI*r2);
weight_ *= exp(result*result/(2*stddev*stddev))*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,
RHEJ::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;
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(
RHEJ::Particle const & parent,
std::vector<Decay> const & decays,
RHEJ::RNG & ran
){
const auto channel = select_decay_channel(decays, ran);
if(channel.products.size() != 2){
throw RHEJ::not_implemented{
"only decays into two particles are implemented"
};
}
std::vector<Particle> decay_products(channel.products.size());
for(size_t i = 0; i < channel.products.size(); ++i){
decay_products[i].type = channel.products[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.;
const double sin_phi = sqrt(1. - cos_phi*cos_phi); // Know 0 < phi < pi
const double px = E*cos(theta)*sin_phi;
const double py = E*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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