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EvtVPHOtoVISR.cpp
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EvtVPHOtoVISR.cpp
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//--------------------------------------------------------------------------
//
// Environment:
// This software is part of the EvtGen package developed jointly
// for the BaBar and CLEO collaborations. If you use all or part
// of it, please give an appropriate acknowledgement.
//
// Copyright Information: See EvtGen/COPYRIGHT
// Copyright (C) 2004 Cornell
//
// Module: EvtVPHOtoVISR.cc
//
// Description: Routine to decay vpho -> vector ISR photon
//
// Modification history:
//
// Ryd March 20, 2004 Module created
//
//------------------------------------------------------------------------
//
#include <stdlib.h>
#include "EvtGenBase/EvtParticle.hh"
#include "EvtGenBase/EvtGenKine.hh"
#include "EvtGenBase/EvtPDL.hh"
#include "EvtGenBase/EvtVector4C.hh"
#include "EvtGenBase/EvtVector4R.hh"
#include "EvtGenBase/EvtReport.hh"
#include "EvtGenBase/EvtRandom.hh"
#include "EvtGenModels/EvtVPHOtoVISR.hh"
#include <string>
EvtVPHOtoVISR::~EvtVPHOtoVISR() {}
std::string EvtVPHOtoVISR::getName(){
return "VPHOTOVISR";
}
EvtDecayBase* EvtVPHOtoVISR::clone(){
return new EvtVPHOtoVISR;
}
void EvtVPHOtoVISR::init(){
// check that there are 0 or 2 arguments
checkNArg(0,2);
// check that there are 2 daughters
checkNDaug(2);
// check the parent and daughter spins
checkSpinParent(EvtSpinType::VECTOR);
checkSpinDaughter(0,EvtSpinType::VECTOR);
checkSpinDaughter(1,EvtSpinType::PHOTON);
}
void EvtVPHOtoVISR::initProbMax() {
//setProbMax(100000.0);
}
void EvtVPHOtoVISR::decay( EvtParticle *p){
//take photon along z-axis, either forward or backward.
//Implement this as generating the photon momentum along
//the z-axis uniformly
double w=p->mass();
double s=w*w;
double L=2.0*log(w/0.000511);
double alpha=1/137.0;
double beta=(L-1)*2.0*alpha/EvtConst::pi;
//This uses the fact that there is a daughter of the
//psi(3770)
assert(p->getDaug(0)->getDaug(0)!=0);
double md=EvtPDL::getMeanMass(p->getDaug(0)->getDaug(0)->getId());
static double mD0=EvtPDL::getMeanMass(EvtPDL::getId("D0"));
static double mDp=EvtPDL::getMeanMass(EvtPDL::getId("D+"));
double pgmax=(s-4.0*md*md)/(2.0*w);
assert(pgmax>0.0);
double pgz=0.99*pgmax*exp(log(EvtRandom::Flat(1.0))/beta);
if (EvtRandom::Flat(1.0)<0.5) pgz=-pgz;
double k=fabs(pgz);
EvtVector4R p4g(k,0.0,0.0,pgz);
EvtVector4R p4res=p->getP4Restframe()-p4g;
double mres=p4res.mass();
double ed=mres/2.0;
assert(ed>md);
double pd=sqrt(ed*ed-md*md);
//std::cout << "k, mres, w, md, ed, pd:"<<k<<" "<<mres<<" "<<w<<" "<<md<<" "<<ed<<" "<<pd<<std::endl;
p->getDaug(0)->init(getDaug(0),p4res);
p->getDaug(1)->init(getDaug(1),p4g);
double sigma=beta*pow(2/w,beta)*(1+alpha*(1.5*L-2.0+EvtConst::pi*EvtConst::pi/3.0)/EvtConst::pi);
double m=EvtPDL::getMeanMass(p->getDaug(0)->getId());
double Gamma=EvtPDL::getWidth(p->getDaug(0)->getId());
//mres is the energy of the psi(3770)
double p0=0.0;
if (ed>mD0) p0=sqrt(ed*ed-mD0*mD0);
double pp=0.0;
if (ed>mDp) pp=sqrt(ed*ed-mDp*mDp);
double p0norm=sqrt(0.25*m*m-mD0*mD0);
double ppnorm=sqrt(0.25*m*m-mDp*mDp);
double r0=12.7;
double rp=12.7;
if (getNArg()==2){
r0=getArg(0);
rp=getArg(1);
}
double GammaTot=Gamma*(pp*pp*pp/(1+pp*pp*rp*rp)+p0*p0*p0/(1+p0*p0*r0*r0))/
(ppnorm*ppnorm*ppnorm/(1+ppnorm*ppnorm*rp*rp)+
p0norm*p0norm*p0norm/(1+p0norm*p0norm*r0*r0));
sigma*=pd*pd*pd/((mres-m)*(mres-m)+0.25*GammaTot*GammaTot);
assert(sigma>0.0);
static double sigmax=sigma;
if (sigma>sigmax){
sigmax=sigma;
}
static int count=0;
count++;
//if (count%10000==0){
// std::cout << "sigma :"<<sigma<<std::endl;
// std::cout << "sigmax:"<<sigmax<<std::endl;
//}
double norm=sqrt(sigma);
vertex(0,0,0,norm*p->eps(0)*p->epsParent(0).conj());
vertex(1,0,0,norm*p->eps(1)*p->epsParent(0).conj());
vertex(2,0,0,norm*p->eps(2)*p->epsParent(0).conj());
vertex(0,1,0,norm*p->eps(0)*p->epsParent(1).conj());
vertex(1,1,0,norm*p->eps(1)*p->epsParent(1).conj());
vertex(2,1,0,norm*p->eps(2)*p->epsParent(1).conj());
vertex(0,2,0,norm*p->eps(0)*p->epsParent(2).conj());
vertex(1,2,0,norm*p->eps(1)*p->epsParent(2).conj());
vertex(2,2,0,norm*p->eps(2)*p->epsParent(2).conj());
vertex(0,0,1,norm*p->eps(0)*p->epsParent(0).conj());
vertex(1,0,1,norm*p->eps(1)*p->epsParent(0).conj());
vertex(2,0,1,norm*p->eps(2)*p->epsParent(0).conj());
vertex(0,1,1,norm*p->eps(0)*p->epsParent(1).conj());
vertex(1,1,1,norm*p->eps(1)*p->epsParent(1).conj());
vertex(2,1,1,norm*p->eps(2)*p->epsParent(1).conj());
vertex(0,2,1,norm*p->eps(0)*p->epsParent(2).conj());
vertex(1,2,1,norm*p->eps(1)*p->epsParent(2).conj());
vertex(2,2,1,norm*p->eps(2)*p->epsParent(2).conj());
return;
}

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