EvtP2GC1.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: EvtP2GC1.cc
//
// Description: Routine to decay psi(2S) to gamma chi_c1 by assuming E1 dominant
//
// Modification history:
//
//    Ping R.-G.       December, 2006       Module created
//
//------------------------------------------------------------------------
//
#include "EvtP2GC1.hh"
#include "../EvtGenBase/EvtGenKine.hh"
#include "../EvtGenBase/EvtHelSys.hh"
#include "../EvtGenBase/EvtPDL.hh"
#include "../EvtGenBase/EvtParticle.hh"
#include "../EvtGenBase/EvtPatches.hh"
#include "../EvtGenBase/EvtReport.hh"
#include "../EvtGenBase/EvtTensor4C.hh"
#include "../EvtGenBase/EvtVector4C.hh"
#include "../EvtGenBase/EvtVector4R.hh"
#include "../EvtGenBase/EvtdFunctionSingle.hh"
#include <stdlib.h>
#include <string>
using std::endl;
 
EvtP2GC1::~EvtP2GC1() {}
 
void EvtP2GC1::getName( std::string& model_name ) { model_name = "P2GC1"; }
 
EvtDecayBase* EvtP2GC1::clone() { return new EvtP2GC1; }
 
void EvtP2GC1::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::VECTOR );
  if ( !( getDaug( 0 ) == GAM ) )
  {
    report( ERROR, "EvtGen" ) << "EvtP2GC1 generator radiative decays expected " << endl;
    ::abort();
  }
}
 
void EvtP2GC1::initProbMax() {
 
  // Hard coded... should not be hard to calculate...
  setProbMax( 1.67 );
}
 
void EvtP2GC1::decay( EvtParticle* p ) {
 
  p->initializePhaseSpace( getNDaug(), getDaugs() );
 
  EvtParticle *v, *s1;
  EvtVector4R  pv, ps, ppr;
 
  v   = p->getDaug( 0 ); // gamma
  s1  = p->getDaug( 1 ); // chi_c1
  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;
  double    alpha = -1. / 3.;
  double    A02   = sqrt( ( 1 + alpha ) / 2 );
  double    A00   = sqrt( ( 1 - alpha ) / 4 );
  double    A12 = -A02, A11 = -A00;
  int       j1, j2, j3;
  for ( j1 = 0; j1 <= 2; )
  {
    for ( j2 = 0; j2 <= 1; )
    {
      for ( j3 = 0; j3 <= 2; )
      {
        vertex( j1, j2, j3, 0.0 );
        j3++;
      }
      j2++;
    }
    j1++;
  }
 
  vertex( 0, 1, 2, Djmn( 1, 1, -1, phi, theta, gamma ) * A12 ); // helicity for psiprime = 1
  vertex( 0, 1, 1, Djmn( 1, 1, 0, phi, theta, gamma ) * A11 );
  vertex( 0, 0, 2, Djmn( 1, 1, 1, phi, theta, gamma ) * A02 );
  vertex( 0, 0, 0, Djmn( 1, 1, 0, phi, theta, gamma ) * A00 );
 
  vertex( 1, 1, 2, Djmn( 1, -1, -1, phi, theta, gamma ) * A12 ); // helicity for psiprime = -1
  vertex( 1, 1, 1, Djmn( 1, -1, 0, phi, theta, gamma ) * A11 );
  vertex( 1, 0, 2, Djmn( 1, -1, 1, phi, theta, gamma ) * A02 );
  vertex( 1, 0, 0, Djmn( 1, -1, 0, phi, theta, gamma ) * A00 );
 
  vertex( 2, 1, 2, Djmn( 1, 0, -1, phi, theta, gamma ) * A12 ); // helicity for psiprime = -1
  vertex( 2, 1, 1, Djmn( 1, 0, 0, phi, theta, gamma ) * A11 );
  vertex( 2, 0, 2, Djmn( 1, 0, 1, phi, theta, gamma ) * A02 );
  vertex( 2, 0, 0, Djmn( 1, 0, 0, phi, theta, gamma ) * A00 );
 
  return;
}