EvtHelPPJ.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, Pang Cai-Ying@IHEP
//
// Module: EvtHelPPJ.hh
//
// Description: To generate psi(2S)->J/psi sigma0->J/psi pi pi.
// using the chiral effective formula: Z.Phys.C73,541 by Mannel
// Modification history:
//
//    Ping R.G. Apr. 2007  created
//------------------------------------------------------------------------
//
#include "EvtHelPPJ.hh"
#include "../EvtGenBase/EvtDiracSpinor.hh"
#include "../EvtGenBase/EvtGenKine.hh"
#include "../EvtGenBase/EvtHelSys.hh"
#include "../EvtGenBase/EvtId.hh"
#include "../EvtGenBase/EvtPDL.hh"
#include "../EvtGenBase/EvtParticle.hh"
#include "../EvtGenBase/EvtPatches.hh"
#include "../EvtGenBase/EvtReport.hh"
#include "../EvtGenBase/EvtVector4C.hh"
#include "../EvtGenBase/EvtdFunction.hh"
#include <iostream>
#include <stdlib.h>
#include <string>
 
using std::cout;
using std::endl;
 
EvtHelPPJ::~EvtHelPPJ() {}
 
void EvtHelPPJ::getName( std::string& model_name ) { model_name = "HelPPJ"; }
 
EvtDecayBase* EvtHelPPJ::clone() { return new EvtHelPPJ; }
 
void EvtHelPPJ::init() {
 
  // check that there are 0 arguments
  checkNArg( 0 );
  checkNDaug( 3 );
 
  checkSpinParent( EvtSpinType::VECTOR );
 
  checkSpinDaughter( 0, EvtSpinType::VECTOR );
  checkSpinDaughter( 1, EvtSpinType::SCALAR );
  checkSpinDaughter( 2, EvtSpinType::SCALAR );
}
 
void EvtHelPPJ::decay( EvtParticle* p ) {
 
  p->initializePhaseSpace( getNDaug(), getDaugs() );
 
  EvtParticle *l1, *l2, *l3;
  l1               = p->getDaug( 0 );
  l2               = p->getDaug( 1 );
  l3               = p->getDaug( 2 );
  EvtVector4R VP4  = l1->getP4(); // Vector Daughter
  EvtVector4R S1P4 = l2->getP4(); // Scalar Daughter
  EvtVector4R S2P4 = l3->getP4(); // Scalar Daughter
  EvtVector4R PRP4 = p->getP4();  // Parent Momentum
  PRP4.set( 1, 0 );
  PRP4.set( 2, 0 );
  PRP4.set( 3, 0 );
 
  double mpipi2 = ( S1P4 + S2P4 ).mass2();
  double e1pi   = S1P4.get( 0 );
  double e2pi   = S2P4.get( 0 );
  double g0     = 0.3;
  double g1     = -0.11;
  double mpi    = 0.1396;
  double mpsi   = 3.097;
  double epsi   = VP4.get( 0 );
  double amp1   = ( mpipi2 - 2 * mpi * mpi ) * g0 / 2 + g1 * e1pi * e2pi;
  double amp0   = amp1 * epsi / mpsi;
 
  EvtHelSys angles( PRP4, VP4 ); // using helicity sys.angles
  double    tht   = angles.getHelAng( 1 );
  double    phi   = angles.getHelAng( 2 );
  double    gamma = 0;
 
  vertex( 0, 0, Djmn( 1, 1, 1, phi, tht, gamma ) * amp1 );
  vertex( 0, 1, Djmn( 1, 1, -1, phi, tht, gamma ) * amp1 );
  vertex( 0, 2, Djmn( 1, 1, 0, phi, tht, gamma ) * amp0 );
  vertex( 1, 0, Djmn( 1, -1, 1, phi, tht, gamma ) * amp1 );
  vertex( 1, 1, Djmn( 1, -1, -1, phi, tht, gamma ) * amp1 );
  vertex( 1, 2, Djmn( 1, -1, 0, phi, tht, gamma ) * amp0 );
  vertex( 2, 0, Djmn( 1, 0, 1, phi, tht, gamma ) * amp1 );
  vertex( 2, 1, Djmn( 1, 0, -1, phi, tht, gamma ) * amp1 );
  vertex( 2, 2, Djmn( 1, 0, 0, phi, tht, gamma ) * amp0 );
 
  return;
}