BesEvtGen-00-04-08/src/EvtGen/EvtGenModels/EvtVPHOtoVISR.cc

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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() {}
 
void EvtVPHOtoVISR::getName(std::string& model_name){
 
  model_name="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;
}