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 "EvtEtaDalitz.hh"
#include "../EvtGenBase/EvtGenKine.hh"
#include "../EvtGenBase/EvtPDL.hh"
#include "../EvtGenBase/EvtParticle.hh"
#include "../EvtGenBase/EvtPatches.hh"
#include "../EvtGenBase/EvtReport.hh"
#include <stdlib.h>
#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;
}