EvtVVPIPI_WEIGHTED.cc

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//--------------------------------------------------------------------------
//
// Environment:
//      This software is part of the EvtGen package developed jointly
//      for the BaBar and CLEO collaborations.  If you use all or part
//      of it, please give an appropriate acknowledgement.
//
// Copyright Information: See EvtGen/COPYRIGHT
//      Copyright (C) 1998      Caltech, UCSB
//
// Module: EvtVVSPwave.cc
//
// Description: Routine to decay vector-> vector pi pi where the
//              decay is S-wave dominated.
//
// Modification history:
//
// Jim Hunt      June 4, 2008 Module Created
//
//------------------------------------------------------------------------
//
#include "EvtVVPIPI_WEIGHTED.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;
 
EvtVVPIPI_WEIGHTED::~EvtVVPIPI_WEIGHTED() {}
 
void EvtVVPIPI_WEIGHTED::getName( std::string& model_name ) { model_name = "VVPIPI_WEIGHTED"; }
 
EvtDecayBase* EvtVVPIPI_WEIGHTED::clone() { return new EvtVVPIPI_WEIGHTED; }
 
void EvtVVPIPI_WEIGHTED::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" ) << "EvtVVPIPI_WEIGHTED generator expected "
                              << " pi+ and pi- (or pi0 and pi0) "
                              << "as 2nd and 3rd daughter. " << endl;
    report( ERROR, "EvtGen" ) << "Will terminate execution!" << endl;
    ::abort();
  }
}
 
void EvtVVPIPI_WEIGHTED::initProbMax() {
  // Hard coded... should not be hard to calculate...
  setProbMax( 0.08 * 1.13 );
}
 
double reweight_event( double pipi_mass ) {
  pipi_mass *= 1000.0;
  return sqrt( -3.6911336508223251 + 0.019119831948029617 * pipi_mass +
               -1.8962883732377376e-05 * pipi_mass * pipi_mass );
}
 
void EvtVVPIPI_WEIGHTED::decay( EvtParticle* psi_prime ) {
 
  psi_prime->initializePhaseSpace( getNDaug(), getDaugs() );
 
  EvtParticle *jpsi, *pi1, *pi2;
 
  jpsi = psi_prime->getDaug( 0 );
  pi1  = psi_prime->getDaug( 1 );
  pi2  = psi_prime->getDaug( 2 );
 
  //  Put phase space results into the daughters.
 
  EvtVector4C ep0, ep1, ep2;
 
  ep0 = psi_prime->eps( 0 );
  ep1 = psi_prime->eps( 1 );
  ep2 = psi_prime->eps( 2 );
 
  EvtVector4C e0, e1, e2;
 
  e0 = jpsi->epsParent( 0 );
  e1 = jpsi->epsParent( 1 );
  e2 = jpsi->epsParent( 2 );
 
  double mass2 = ( pi1->getP4() + pi2->getP4() ).mass2();
 
  double fac = mass2 - 4 * pi1->mass() * pi2->mass();
 
  fac *= reweight_event( sqrt( mass2 ) );
 
  vertex( 0, 0, fac * ( ep0 * e0.conj() ) );
  vertex( 0, 1, fac * ( ep0 * e1.conj() ) );
  vertex( 0, 2, fac * ( ep0 * e2.conj() ) );
 
  vertex( 1, 0, fac * ( ep1 * e0.conj() ) );
  vertex( 1, 1, fac * ( ep1 * e1.conj() ) );
  vertex( 1, 2, fac * ( ep1 * e2.conj() ) );
 
  vertex( 2, 0, fac * ( ep2 * e0.conj() ) );
  vertex( 2, 1, fac * ( ep2 * e1.conj() ) );
  vertex( 2, 2, fac * ( ep2 * e2.conj() ) );
 
  return;
}