EvtP2GC0.cc

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//--------------------------------------------------------------------------
//
// Environment:
//      This software is part of models developed at BES collaboration
//      based on the EvtGen framework.  If you use all or part
//      of it, please give an appropriate acknowledgement.
//
// Copyright Information: See EvtGen/BesCopyright
//      Copyright (A) 2006      Ping Rong-Gang @IHEP
//
// Module: EvtP2GC0.cc
//
// Description: Routine to decay psi(2S) to gamma chi_c0 by assuming E1 dominant
//              
// Modification history:
//
//    Ping R.-G.       December, 2006       Module created
//
//------------------------------------------------------------------------
// 
#include "EvtGenBase/EvtPatches.hh"
#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/EvtTensor4C.hh"
#include "EvtGenBase/EvtReport.hh"
#include "EvtGenBase/EvtdFunction.hh"
#include "EvtGenBase/EvtHelSys.hh"
#include "EvtP2GC0.hh"
#include <string>
using std::endl;
 
EvtP2GC0::~EvtP2GC0() {}
 
void EvtP2GC0::getName(std::string& model_name){
 
  model_name="P2GC0";     
 
}
 
 
EvtDecayBase* EvtP2GC0::clone(){
 
  return new EvtP2GC0;
 
}
 
void EvtP2GC0::init(){
static EvtId GAM=EvtPDL::getId("gamma");
// check that there are 0 arguments
 checkNArg(0); 
 checkNDaug(2);
 checkSpinParent(EvtSpinType::VECTOR);
 checkSpinDaughter(0,EvtSpinType::PHOTON);
 checkSpinDaughter(1,EvtSpinType::SCALAR);
 if (!(getDaug(0)==GAM)) {
 report(ERROR,"EvtGen") << "EvtP2GC0 generator radiative decays expected "<<endl;
 ::abort();
}
 }
 
 
void EvtP2GC0::initProbMax() {
 
  //Hard coded... should not be hard to calculate...
 setProbMax(1.0);
 
}      
 
void EvtP2GC0::decay( EvtParticle *p){
 
  p->initializePhaseSpace(getNDaug(),getDaugs());
 
  EvtParticle *v,*s1;
  EvtVector4R pv,ps,ppr;
  
  v =p->getDaug(0);  //gamma
  s1=p->getDaug(1); //chi_c0
  pv=v->getP4();
  ps=s1->getP4();
  ppr=p->getP4();
//  Put phase space results into the daughters.
  EvtHelSys angles(ppr,pv); //using helicity sys. angles
  double theta =angles.getHelAng(1); 
  double phi   =angles.getHelAng(2);
  double gamma =0;
 
 int j1,j2,j3;
 for(j1=0;j1<=1;){
 for(j2=0;j2<=1;){
 vertex(j1,j2,0.0);j2++;}
j1++;}
 
// since the spin density matrix for psi(2s) is
//      Dimension:3
//    (1,0) (0,0) (0,0) 
//    (0,0) (1,0) (0,0) 
//    (0,0) (0,0) (0,0) 
 
 vertex(0,1,Djmn(1, 1,-1,phi,theta,gamma));  // psi(2S) helicity =1 corresponding index=0
 vertex(0,0,Djmn(1, 1, 1,phi,theta,gamma));
 vertex(2,1,Djmn(1, 0,-1,phi,theta,gamma)); // psi(2S) helicity =0 corresponding index=2 
 vertex(2,0,Djmn(1, 0, 1,phi,theta,gamma));
 vertex(1,1,Djmn(1,-1,-1,phi,theta,gamma));  // psi(2S) helicity =-1 corresponding index=1
 vertex(1,0,Djmn(1,-1, 1,phi,theta,gamma));
 
  return ;
 
}