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PomeronFlux.cc
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PomeronFlux.cc
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// -*- C++ -*-
//
// This is the implementation of the non-inlined, non-templated member
// functions of the PomeronFlux class.
//
#include "PomeronFlux.h"
#include "ThePEG/Utilities/DescribeClass.h"
#include "ThePEG/Utilities/Maths.h"
#include "ThePEG/Interface/ClassDocumentation.h"
#include "ThePEG/Persistency/PersistentOStream.h"
#include "ThePEG/Persistency/PersistentIStream.h"
#include "ThePEG/Interface/Parameter.h"
#include "ThePEG/Interface/Switch.h"
#include "ThePEG/PDT/ParticleData.h"
#include "ThePEG/PDT/EnumParticles.h"
#include "ThePEG/StandardModel/StandardModelBase.h"
#include "ThePEG/Repository/EventGenerator.h"
using namespace ThePEG;
using namespace Herwig;
PomeronFlux::PomeronFlux()
: q2min_(ZERO) , q2max_(10.*GeV2),
xiMin_(1.0e-7) , xiMax_(1.0),
alfa0P_(1.104) , alfapP_(0.06/GeV2),
betaP_(5.5/GeV2), normP_(1./GeV2),
alfa0R_(0.5) , alfapR_(0.3/GeV2),
betaR_(1.6/GeV2), normR_(1./GeV2),
nR_(0.0013) , PDFFit_(0)
{}
bool PomeronFlux::canHandleParticle(tcPDPtr particle) const {
return ( abs(particle->id()) == ParticleID::pplus );
}
cPDVector PomeronFlux::partons(tcPDPtr) const {
cPDVector ret;
ret.push_back(getParticleData( ParticleID::pomeron));
ret.push_back(getParticleData( ParticleID::reggeon));
return ret;
}
double PomeronFlux::xfl(tcPDPtr, tcPDPtr parton, Energy2 qq,
double l, Energy2 ) const {
// extra factor of Q^2 to cancel jacobian and sort out dimensions
if(parton->id()==ParticleID::pomeron)
return normP_*qq*exp(-(betaP_ + 2.*alfapP_*l)*qq + 2.*(alfa0P_ - 1)*l);
else if(parton->id()==ParticleID::reggeon)
return nR_*normR_*qq*exp(-(betaR_ + 2.*alfapR_*l)*qq + 2.*(alfa0R_ - 1)*l);
else {
assert(false);
return 0.;
}
}
double PomeronFlux::xfvl(tcPDPtr, tcPDPtr, Energy2, double,
Energy2) const {
// valence density is zero
return 0.0;
}
// The following static variable is needed for the type
// description system in ThePEG.
DescribeClass<PomeronFlux,PDFBase>
describeHerwigPomeronFlux("Herwig::PomeronFlux", "HwPomeronFlux.so");
void PomeronFlux::Init() {
static ClassDocumentation<PomeronFlux> documentation
("The PomeronFlux provides the PDF for a pomeron inside"
" an incoming proton");
static Parameter<PomeronFlux,Energy2> interfaceQ2Min
("Q2Min",
"Minimum value of the magnitude of Q^2 for the pomeron/reggeon",
&PomeronFlux::q2min_, GeV2, ZERO, ZERO, 100.0*GeV2,
false, false, Interface::limited);
static Parameter<PomeronFlux,Energy2> interfaceQ2Max
("Q2Max",
"Maximum value of the magnitude of Q^2 for the pomeron/reggeon",
&PomeronFlux::q2max_, GeV2, 4.0*GeV2, ZERO, 100.0*GeV2,
false, false, Interface::limited);
static Parameter<PomeronFlux,double> interfaceXiMin
("XiMin",
"Minimum value of the pomeron/reggeon xi",
&PomeronFlux::xiMin_, 1.0e-7 , 0., 1.,
false, false, Interface::limited);
static Parameter<PomeronFlux,double> interfaceXiMax
("XiMax",
"Maximum value of the pomeron/reggeon xi",
&PomeronFlux::xiMax_, 1., 0., 1.,
false, false, Interface::limited);
static Parameter<PomeronFlux,double> interfaceAlpha0Pomeron
("Alpha0Pomeron",
"The coefficient of the intercept of alpha pomeron",
&PomeronFlux::alfa0P_, 1.104, 0.0, 0,
true, false, Interface::lowerlim);
static Parameter<PomeronFlux,InvEnergy2> interfaceAlphaPrimePomeron
("AlphaPrimePomeron",
"The coefficient of the t dependence of alpha of pomeron",
&PomeronFlux::alfapP_, 1./GeV2, 0.06/GeV2, 0./GeV2, 1./GeV2,
false, false, Interface::limited);
static Parameter<PomeronFlux,InvEnergy2> interfaceBPomeron
("BPomeron",
"The coefficient of the t dependence of the exponential term of pomeron",
&PomeronFlux::betaP_, 1./GeV2, 5.5/GeV2, 0./GeV2, 10./GeV2,
false, false, Interface::limited);
static Parameter<PomeronFlux,double> interfaceAlpha0Reggeon
("Alpha0Reggeon",
"The coefficient of the intercept of alpha reggeon",
&PomeronFlux::alfa0R_, 0.5, 0.0, 0,
true, false, Interface::lowerlim);
static Parameter<PomeronFlux,InvEnergy2> interfaceAlphaPrimeReggeon
("AlphaPrimeReggeon",
"The coefficient of the t dependence of alpha of reggeon",
&PomeronFlux::alfapR_, 1./GeV2, 0.3/GeV2, 0./GeV2, 1./GeV2,
false, false, Interface::limited);
static Parameter<PomeronFlux,InvEnergy2> interfaceBReggeon
("BReggeon",
"The coefficient of the t dependence of the exponential term reggeon",
&PomeronFlux::betaR_, 1/GeV2, 1.6/GeV2, 0./GeV2, 10./GeV2,
false, false, Interface::limited);
static Parameter<PomeronFlux,double> interfacenR
("nR",
"Reggeon flux factor",
&PomeronFlux::nR_, 0.0017, 0.0, 0,
true, false, Interface::lowerlim);
static Switch<PomeronFlux,int> interfacePDFFit
("PDFFit",
"The pomeron/regeon flux parameters are set according"
" to choice of pomeron/regeon structure function fit. ",
&PomeronFlux::PDFFit_, 0, false, false);
static SwitchOption interfacePDFFitUser
(interfacePDFFit,
"User",
"Default (set for fit Hera 2007) or user setting.",
0);
static SwitchOption interfacePDFFitPomeron2007
(interfacePDFFit,
"Pomeron2007",
"Pomeron structure function fit is Hera 2007.",
1);
static SwitchOption interfacePDFFitPomeron2006A
(interfacePDFFit,
"Pomeron2006A",
"Pomeron structure function fit is Hera 2006 A.",
2);
static SwitchOption interfacePDFFitPomeron2006B
(interfacePDFFit,
"Pomeron2006B",
"Pomeron structure function fit is Hera 2006 B.",
3);
}
double PomeronFlux::flattenScale(tcPDPtr proton, tcPDPtr parton, const PDFCuts & c,
double l, double z, double & jacobian) const {
double x = exp(-l);
Energy2 qqmax = min(q2max_,0.25*sqr(x)*c.sMax());
Energy2 qqmin = max(q2min_, sqr(proton->mass()*x)/(1-x));
if(qqmin>=qqmax) {
jacobian = 0.;
return 0.;
}
InvEnergy2 k =ZERO;
if(parton->id()==ParticleID::pomeron)
k = betaP_ + 2.*l*alfapP_;
else if(parton->id()==ParticleID::reggeon)
k = betaR_ + 2.*l*alfapR_;
else assert(false);
double rho = exp(-k*qqmax) + z * ( exp(-k*qqmin) - exp(-k*qqmax) );
Energy2 scale = -log(rho)/k;
// jacobian factor (1/Q^2max_)(dQ^2/dz) / Q^2 (to make dimensionless)
jacobian *= (exp(-k*qqmin) - exp(-k*qqmax))/(rho*k*scale);
// return Q^2/Q^2_max
return scale/c.scaleMaxL(l);
}
double PomeronFlux::flattenL(tcPDPtr, tcPDPtr parton, const PDFCuts&,
double z, double & jacobian) const {
const double lMax = -log(xiMin_);
const double lMin = -log(xiMax_);
// cout<<"lMin "<<lMin<<" lMax "<<lMax<<endl;
if(parton->id()==ParticleID::pomeron) {
jacobian *= lMax - lMin;
return lMin + z*(lMax - lMin);
}
else if(parton->id()==ParticleID::reggeon) {
double k = 2.*(alfa0R_ - 1.);
double rho =exp(k*lMin) + z*(exp(k*lMax) - exp(k*lMin));
jacobian *= (exp(k*lMax) - exp(k*lMin))/(rho*k);
return log(rho)/k;
}
else {
assert(false);
return 0.;
}
}
Energy2 PomeronFlux::intxFx(double x, Energy2 qqmin, Energy2 qqmax,
double alfa0, InvEnergy2 alfap, InvEnergy2 beta) const {
InvEnergy2 k = beta - 2.*log(x)*alfap;
return exp(-2.*(alfa0 - 1.)*log(x))*(exp(-qqmin*k) - exp(-qqmax*k))/k;
}
void PomeronFlux::persistentOutput(PersistentOStream & os) const {
os << ounit(q2min_,GeV2) << ounit(q2max_,GeV2) << xiMin_ << xiMax_ << alfa0P_
<< ounit(alfapP_,1./GeV2) << ounit(betaP_,1./GeV2) << ounit(normP_,1./GeV2)
<< alfa0R_ << ounit(alfapR_,1./GeV2) << ounit(betaR_,1./GeV2)
<< ounit(normR_,1./GeV2) << nR_ << PDFFit_;
}
void PomeronFlux::persistentInput(PersistentIStream & is, int) {
is >> iunit(q2min_,GeV2) >> iunit(q2max_,GeV2) >> xiMin_ >> xiMax_ >> alfa0P_
>> iunit(alfapP_,1./GeV2) >> iunit(betaP_,1./GeV2) >> iunit(normP_,1./GeV2)
>> alfa0R_ >> iunit(alfapR_,1./GeV2) >> iunit(betaR_,1./GeV2)
>> iunit(normR_,1./GeV2) >> nR_ >> PDFFit_;
}
void PomeronFlux::doinit() {
PDFBase::doinit();
setFluxPar();
// compute the normalisation factor
double xp = 0.003;
Energy2 tkinmin = sqr(getParticleData(ParticleID::pplus)->mass()*xp)/(1-xp);
normP_ = 1./(intxFx(xp,tkinmin , 1.*GeV2, alfa0P_, alfapP_, betaP_ ));
normR_ = 1./(intxFx(xp,tkinmin , 1.*GeV2, alfa0R_, alfapR_, betaR_ ));
}
void PomeronFlux::setFluxPar() {
switch(PDFFit_){
case 0:
break;
case 1:
alfa0P_ = 1.104;
nR_ = 0.0013;
break;
case 2:
alfa0P_ = 1.118;
nR_ = 0.0017;
break;
case 3:
alfa0P_ = 1.111;
nR_ = 0.0014;
break;
default:
throw Exception() << "Invalid fit in PomeronFlux::setFluxPar()"
<< Exception::runerror;
}
}

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