//--------------------------------------------------------------------------
//
// 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() {}

std::string EvtEtaDalitz::getName(){

  return "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 2565 (1973).

  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 ;
   
}