EvtT2GV.cc

Go to the documentation of this file.

//--------------------------------------------------------------------------
//
// 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:  EvtT2GV.cc
//
// Description: Routine to decay chi_c2-> gamma J/psi
//
// Modification history:
//
//    Ping R.-G.       December, 2006       Module created
//
//------------------------------------------------------------------------
 
//
#include "EvtT2GV.hh"
#include "../EvtGenBase/EvtGenKine.hh"
#include "../EvtGenBase/EvtHelSys.hh"
#include "../EvtGenBase/EvtPDL.hh"
#include "../EvtGenBase/EvtParticle.hh"
#include "../EvtGenBase/EvtPatches.hh"
#include "../EvtGenBase/EvtRandom.hh"
#include "../EvtGenBase/EvtReport.hh"
#include "../EvtGenBase/EvtTensor4C.hh"
#include "../EvtGenBase/EvtVector4C.hh"
#include "../EvtGenBase/EvtVector4R.hh"
#include <stdlib.h>
 
#include <string>
 
EvtT2GV::~EvtT2GV() {}
 
void EvtT2GV::getName( std::string& model_name ) { model_name = "T2GV"; }
 
EvtDecayBase* EvtT2GV::clone() { return new EvtT2GV; }
 
void EvtT2GV::init() {
 
  // check that there are 0 arguments
  checkNArg( 0 );
}
 
void EvtT2GV::initProbMax() {
 
  //  noProbMax();
  setProbMax( 30.00001 );
}
 
void EvtT2GV::decay( EvtParticle* p ) {
 
loop:
  p->initializePhaseSpace( getNDaug(), getDaugs() );
  EvtParticle *v, *s1;
  EvtVector4R  pv, ps, ppr;
 
  v   = p->getDaug( 0 ); // gamma
  s1  = p->getDaug( 1 ); // J/psi
  pv  = v->getP4();
  ps  = s1->getP4();
  ppr = p->getP4();
 
  double alpha = 21. / 73.;
  //  Put phase space results into the daughters.
  //  EvtHelSys angles(ppr,pv); //using helicity sys. angles
  EvtHelSys angles( ps, pv );
  double    theta = angles.getHelAng( 1 );
  double    phi   = angles.getHelAng( 2 );
  double    gamma = 0;
  double    F0    = 1.;
  double    F1    = sqrt( 3. ) * F0; // pure M1 transition assumed,see PRD13,p1203
  double    F2 = sqrt( 6. ) * F0; // helicity amplitude is labeled with lambda_chi and photon
 
  int j1, j2, j3;
  for ( j1 = 0; j1 <= 4; )
  {
    for ( j2 = 0; j2 <= 1; )
    {
      for ( j3 = 0; j3 <= 2; )
      {
        vertex( j1, j2, j3, 0.0 );
        j3++;
      }
      j2++;
    }
    j1++;
  }
 
  vertex( 0, 0, 0, Djmn( 1, 1, 1, phi, theta, gamma ) * F0 );
  vertex( 0, 0, 1, Djmn( 1, -1, 1, phi, theta, gamma ) * F0 );
  vertex( 0, 0, 2, Djmn( 1, 0, 1, phi, theta, gamma ) * F0 );
  vertex( 0, 1, 0, Djmn( 1, 1, -1, phi, theta, gamma ) * F0 );
  vertex( 0, 1, 1, Djmn( 1, -1, -1, phi, theta, gamma ) * F0 );
  vertex( 0, 1, 2, Djmn( 1, 0, -1, phi, theta, gamma ) * F0 );
 
  vertex( 1, 0, 0, Djmn( 1, 1, -1, phi, theta, gamma ) * F2 );
  vertex( 1, 0, 1, Djmn( 1, -1, -1, phi, theta, gamma ) * F2 );
  vertex( 1, 0, 2, Djmn( 1, 0, -1, phi, theta, gamma ) * F2 );
 
  vertex( 2, 1, 0, Djmn( 1, 1, 1, phi, theta, gamma ) * F2 );
  vertex( 2, 1, 1, Djmn( 1, -1, 1, phi, theta, gamma ) * F2 );
  vertex( 2, 1, 2, Djmn( 1, 0, 1, phi, theta, gamma ) * F2 );
 
  vertex( 3, 0, 0, Djmn( 1, 1, 0, phi, theta, gamma ) * F1 );
  vertex( 3, 0, 1, Djmn( 1, -1, 0, phi, theta, gamma ) * F1 );
  vertex( 3, 0, 2, Djmn( 1, 0, 0, phi, theta, gamma ) * F1 );
 
  vertex( 4, 1, 0, Djmn( 1, 1, 0, phi, theta, gamma ) * F1 );
  vertex( 4, 1, 1, Djmn( 1, -1, 0, phi, theta, gamma ) * F1 );
  vertex( 4, 1, 2, Djmn( 1, 0, 0, phi, theta, gamma ) * F1 );
 
  return;
}