BesEvtGen-00-04-08/src/EvtGen/EvtGenModels/EvtEtaDalitz.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: EvtEtaDalitz.cc
//
// Description: Routine to decay eta -> pi+ pi- pi0
//
// Modification history:
//
//    DJL/RYD     July 23, 1997        Module created
//
//------------------------------------------------------------------------
// 
#include "EvtGenBase/EvtPatches.hh"
#include <stdlib.h>
#include "EvtGenBase/EvtParticle.hh"
#include "EvtGenBase/EvtGenKine.hh"
#include "EvtGenBase/EvtPDL.hh"
#include "EvtGenModels/EvtEtaDalitz.hh"
#include "EvtGenBase/EvtReport.hh"
#include <string>
 
EvtEtaDalitz::~EvtEtaDalitz() {}
 
void EvtEtaDalitz::getName(std::string& model_name){
 
  model_name="ETA_DALITZ";     
 
}
 
 
EvtDecayBase* EvtEtaDalitz::clone(){
 
  return new EvtEtaDalitz;
 
}
 
void EvtEtaDalitz::init(){
 
  // check that there are 0 arguments
  checkNArg(0);
  checkNDaug(3);
 
  checkSpinParent(EvtSpinType::SCALAR);
 
  checkSpinDaughter(0,EvtSpinType::SCALAR);
  checkSpinDaughter(1,EvtSpinType::SCALAR);
  checkSpinDaughter(2,EvtSpinType::SCALAR);
}
 
 
void EvtEtaDalitz::initProbMax(){
 
  setProbMax(2.1);
 
}
 
void EvtEtaDalitz::decay( EvtParticle *p){
 
  p->initializePhaseSpace(getNDaug(),getDaugs());
 
  EvtVector4R mompi0 = p->getDaug(2)->getP4();
  double masspip = p->getDaug(0)->mass();
  double masspim = p->getDaug(1)->mass();
  double masspi0 = p->getDaug(2)->mass();
  double m_eta = p->mass();
 
  double y;
 
  //The decay amplitude coems from Layter et al PRD 7 pA2M5.
  //this reference doesn't make sence!!!
 
  y=(mompi0.get(0)-masspi0)*(3.0/(m_eta-masspip-masspim-masspi0))-1.0;
 
  EvtComplex amp(sqrt(1.0-1.07*y),0.0);
 
  vertex(amp);
 
  return ;
   
}