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 "EvtGenBase/EvtPatches.hh"
#include <stdlib.h>
#include "EvtGenBase/EvtParticle.hh"
#include "EvtGenBase/EvtGenKine.hh"
#include "EvtGenBase/EvtPDL.hh"
#include "EvtGenBase/EvtVector4C.hh"
#include "EvtGenBase/EvtTensor4C.hh"
#include "EvtGenBase/EvtReport.hh"
#include "EvtGenModels/EvtVVPIPI_WEIGHTED.hh"
#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 ;
 
}