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diff --git a/Shower/QTilde/SplittingFunctions/OneHalfHalfSplitFn.cc b/Shower/QTilde/SplittingFunctions/OneHalfHalfSplitFn.cc
--- a/Shower/QTilde/SplittingFunctions/OneHalfHalfSplitFn.cc
+++ b/Shower/QTilde/SplittingFunctions/OneHalfHalfSplitFn.cc
@@ -1,219 +1,221 @@
// -*- C++ -*-
//
// OneHalfHalfSplitFn.cc is a part of Herwig - A multi-purpose Monte Carlo event generator
// Copyright (C) 2002-2019 The Herwig Collaboration
//
// Herwig is licenced under version 3 of the GPL, see COPYING for details.
// Please respect the MCnet academic guidelines, see GUIDELINES for details.
//
//
// This is the implementation of the non-inlined, non-templated member
// functions of the OneHalfHalfSplitFn class.
//
#include "OneHalfHalfSplitFn.h"
#include "ThePEG/PDT/ParticleData.h"
#include "ThePEG/Interface/ClassDocumentation.h"
#include "ThePEG/Utilities/DescribeClass.h"
#include "Herwig/Decay/TwoBodyDecayMatrixElement.h"
#include "Herwig/Shower/QTilde/QTildeShowerHandler.h"
using namespace Herwig;
DescribeNoPIOClass<OneHalfHalfSplitFn,Herwig::Sudakov1to2FormFactor>
describeOneHalfHalfSplitFn ("Herwig::OneHalfHalfSplitFn","HwShower.so");
void OneHalfHalfSplitFn::Init() {
static ClassDocumentation<OneHalfHalfSplitFn> documentation
("The OneHalfHalfSplitFn class implements the splitting function for g->q qbar");
}
double OneHalfHalfSplitFn::integOverP(const double z, const IdList &,
unsigned int PDFfactor) const {
switch(PDFfactor) {
case 0:
return z;
case 1:
return log(z);
case 2:
return -log(1.-z);
case 3:
return log(z/(1.-z));
case 4:
return 2.*sqrt(z);
case 5:
return (2./3.)*z*sqrt(z);
default:
throw Exception() << "OneHalfHalfSplitFn::integOverP() invalid PDFfactor = "
<< PDFfactor << Exception::runerror;
}
}
double OneHalfHalfSplitFn::invIntegOverP(const double r,
const IdList &,
unsigned int PDFfactor) const {
switch(PDFfactor) {
case 0:
return r;
case 1:
return exp(r);
case 2:
return 1.-exp(-r);
case 3:
return 1./(1.+exp(-r));
case 4:
return 0.25*sqr(r);
case 5:
return pow(1.5*r,2./3.);
default:
throw Exception() << "OneHalfHalfSplitFn::integOverP() invalid PDFfactor = "
<< PDFfactor << Exception::runerror;
}
}
vector<pair<int, Complex> >
OneHalfHalfSplitFn::generatePhiForward(const double z, const Energy2 t, const IdList & ids,
const RhoDMatrix & rho) {
assert(rho.iSpin()==PDT::Spin1);
double modRho = abs(rho(0,2));
Energy mq = ids[1]->mass();
Energy2 mq2 = sqr(mq);
double fact = z*(1.-z)-mq2/t;
double max = 1.+2.*fact*(-1.+2.*modRho);
vector<pair<int, Complex> > output;
output.push_back(make_pair( 0,(rho(0,0)+rho(2,2))*(1.-2.*fact)/max));
output.push_back(make_pair(-2,2.*fact*rho(0,2)/max));
output.push_back(make_pair( 2,2.*fact*rho(2,0)/max));
return output;
}
DecayMEPtr OneHalfHalfSplitFn::matrixElement(const double z, const Energy2 t,
const IdList & ids, const double phi,
bool timeLike) {
static const Complex ii(0.,1.);
// calculate the kernal
DecayMEPtr kernal(new_ptr(TwoBodyDecayMatrixElement(PDT::Spin1,PDT::Spin1Half,PDT::Spin1Half)));
double mt = !timeLike ? ZERO : ids[1]->mass()/sqrt(t);
double root =sqrt(1.-sqr(mt)/z/(1.-z));
(*kernal)(0,0,0) = mt/sqrt(z*(1.-z));
(*kernal)(2,1,1) = (*kernal)(0,0,0);
(*kernal)(0,0,1) = -z*root*exp(-ii*phi);
(*kernal)(2,1,0) = -conj((*kernal)(0,0,1));
(*kernal)(0,1,0) = (1.-z)*exp(-ii*phi)*root;
(*kernal)(2,0,1) = -conj((*kernal)(0,1,0));
(*kernal)(0,1,1) = 0.;
(*kernal)(2,0,0) = 0.;
return kernal;
}
void OneHalfHalfSplitFn::findZero() {
const double xTest = 0.2;
vector<Energy2> m2;
for(int id=4;id<=6;++id) {
tPDPtr parton = getParticleData(id);
Energy2 sMin(0.5*GeV2),sMax(4.*sqr(parton->mass()));
// ensure min and max in correct regions
while (PDF()->xfx(beam(),parton,sMin,xTest)!=0. && sMin>0.01*GeV2) {
sMin *=0.5;
}
while (PDF()->xfx(beam(),parton,sMax,xTest)==0. && sMax<1e10*GeV2) {
sMax *=2.;
}
if(sMin<0.01*GeV2 || sMax>1e10*GeV2) {
m2.push_back(ZERO);
continue;
}
// bisect to find zero
while(sMax-sMin>1e-10*GeV2) {
Energy2 sMid = 0.5*(sMax+sMin);
double test = PDF()->xfx(beam(),parton,sMid,xTest);
if(test!=0.) sMax = sMid;
else sMin = sMid;
}
m2.push_back(sMin);
}
mq_[PDF()] = m2;
}
void OneHalfHalfSplitFn::guesstz(Energy2 t1,unsigned int iopt,
const IdList &ids,
double enhance,bool ident,
double detune,
Energy2 &t_main, double &z_main) {
mq2_ = ZERO;
// get the mass to fix
if(iopt==1 && abs(ids[1]->id())>3) {
map<cPDFPtr,vector<Energy2>>::const_iterator cit = mq_.find(PDF());
if(cit== mq_.end()) findZero();
cit = mq_.find(PDF());
mq2_ = cit->second[abs(ids[1]->id())-4];
+ if(t1-mq2_<1e-10*GeV2) {
+ t_main = ZERO;
+ return;
+ }
}
unsigned int pdfopt = iopt!=1 ? 0 : pdfFactor();
double lower = integOverP(zLimits().first ,ids,pdfopt);
double upper = integOverP(zLimits().second,ids,pdfopt);
double c = 1./((upper - lower) * colourFactor()
* alpha()->showerOverestimateValue()/Constants::twopi*enhance*detune);
double r = UseRandom::rnd();
assert(iopt<=2);
if(iopt==1) {
c/=pdfMax();
//symmetry of FS gluon splitting
if(ident) c*=0.5;
}
else if(iopt==2) c*=-1.;
// guessing t
if(mq2_!=ZERO) {
t_main = (t1-mq2_)*pow(r,c) + mq2_;
}
else {
if(iopt!=2 || c*log(r)<log(Constants::MaxEnergy2/t1)) {
t_main = t1*pow(r,c);
}
else
t_main = Constants::MaxEnergy2;
}
// guessing z
z_main = invIntegOverP(lower + UseRandom::rnd()
*(upper - lower),ids,pdfopt);
}
double OneHalfHalfSplitFn::PDFVetoRatio(const Energy2 t, const double x, const double z,
const tcPDPtr parton0, const tcPDPtr parton1,double factor) const {
assert(PDF());
Energy2 theScale = t * sqr(ShowerHandler::currentHandler()->factorizationScaleFactor()*factor);
if (theScale < sqr(freeze())) theScale = sqr(freeze());
const double newpdf=PDF()->xfx(beam(),parton0,theScale,x/z);
if(newpdf<=0.) return 0.;
const double oldpdf=PDF()->xfx(beam(),parton1,theScale,x);
if(oldpdf<=0.) return 1.;
double ratio = newpdf/oldpdf;
double maxpdf = pdfMax();
- if(mq2_!=ZERO) ratio *= (t-mq2_)/t;
-
+ if(mq2_!=ZERO) {
+ ratio *= (t-mq2_)/t;
+ }
switch (pdfFactor()) {
case 0: break;
case 1: maxpdf /= z; break;
case 2: maxpdf /= 1.-z; break;
case 3: maxpdf /= (z*(1.-z)); break;
case 4: maxpdf /= sqrt(z); break;
case 5: maxpdf *= sqrt(z); break;
default :
throw Exception() << "OneHalfHalfSplitFn::PDFVetoRatio invalid PDFfactor = "
<< pdfFactor() << Exception::runerror;
}
- if (ratio > maxpdf) {
+ if (ratio > maxpdf && (mq2_==ZERO || (mq2_!=ZERO && (t-mq2_)/t >1e-6 ) ) )
generator()->log() << "OneHalfHalfSplitFn::PDFVetoRatio PDFVeto warning: Ratio > " << name()
- << ":PDFmax (by a factor of "
- << ratio/maxpdf <<") for "
- << parton0->PDGName() << " to "
- << parton1->PDGName() << "\n";
- }
+ << ":PDFmax (by a factor of " << ratio/maxpdf <<") for "
+ << parton0->PDGName() << " to " << parton1->PDGName() << " " << (t-mq2_)/t << "\n";
return ratio/maxpdf ;
}

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