EvtJpipi.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: EvtJpipi.cc
//
// Description: Routine to decay psi(2S)-> J/psi pi pi using chiral Lagrangian and
//      information by fitting the exp. data
//
// Modification history:
//
//    Ping R.-G.       December, 2006       Module created
//
//------------------------------------------------------------------------
//
#include "EvtJpipi.hh"
#include "../EvtGenBase/EvtGenKine.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 <stdlib.h>
#include <string>
using std::endl;
 
EvtJpipi::~EvtJpipi() {}
 
void EvtJpipi::getName( std::string& model_name ) { model_name = "JPIPI"; }
 
EvtDecayBase* EvtJpipi::clone() { return new EvtJpipi; }
 
void EvtJpipi::init() {
 
  static EvtId PIP = EvtPDL::getId( "pi+" );
  static EvtId PIM = EvtPDL::getId( "pi-" );
  static EvtId PI0 = EvtPDL::getId( "pi0" );
 
  // check that there are 0 arguments
  checkNArg( 0 );
  checkNDaug( 3 );
 
  checkSpinParent( EvtSpinType::VECTOR );
  checkSpinDaughter( 0, EvtSpinType::VECTOR );
 
  if ( ( !( getDaug( 1 ) == PIP && getDaug( 2 ) == PIM ) ) &&
       ( !( getDaug( 1 ) == PI0 && getDaug( 2 ) == PI0 ) ) )
  {
    report( ERROR, "EvtGen" ) << "EvtJpipi generator expected "
                              << " pi+ and pi- (or pi0 and pi0) "
                              << "as 2nd and 3rd daughter. " << endl;
    report( ERROR, "EvtGen" ) << "Will terminate execution!" << endl;
    ::abort();
  }
}
 
void EvtJpipi::initProbMax() {
 
  // Hard coded... should not be hard to calculate...
  setProbMax( 0.019 );
}
 
void EvtJpipi::decay( EvtParticle* p ) {
 
  p->initializePhaseSpace( getNDaug(), getDaugs() );
 
  EvtParticle *v, *s1, *s2;
 
  v  = p->getDaug( 0 );
  s1 = p->getDaug( 1 );
  s2 = p->getDaug( 2 );
 
  //  Put phase space results into the daughters.
 
  EvtVector4C ep0, ep1, ep2;
 
  ep0 = p->eps( 0 );
  ep1 = p->eps( 1 );
  ep2 = p->eps( 2 );
 
  //  double fac=(s1->getP4()+s2->getP4()).mass2()-4*s1->mass()*s2->mass();
  double fac1 = ( s1->getP4() + s2->getP4() ).mass2() - 2 * s1->mass() * s2->mass();
  double fac  = 0.3 * fac1 - 2 * 0.11 * ( s1->getP4() ).get( 0 ) * ( s2->getP4() ).get( 0 );
 
  vertex( 0, 0, fac * ( ep0 * v->epsParent( 0 ).conj() ) );
  vertex( 0, 1, fac * ( ep0 * v->epsParent( 1 ).conj() ) );
  vertex( 0, 2, fac * ( ep0 * v->epsParent( 2 ).conj() ) );
 
  vertex( 1, 0, fac * ( ep1 * v->epsParent( 0 ).conj() ) );
  vertex( 1, 1, fac * ( ep1 * v->epsParent( 1 ).conj() ) );
  vertex( 1, 2, fac * ( ep1 * v->epsParent( 2 ).conj() ) );
 
  vertex( 2, 0, fac * ( ep2 * v->epsParent( 0 ).conj() ) );
  vertex( 2, 1, fac * ( ep2 * v->epsParent( 1 ).conj() ) );
  vertex( 2, 2, fac * ( ep2 * v->epsParent( 2 ).conj() ) );
 
  return;
}