EvtRhoPi.cc

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//--------------------------------------------------------------------------
//
// Environment:
//      This software is part of models developed at BES collaboration
//      based on the EvtGen framework.  If you use all or part
//      of it, please give an appropriate acknowledgement.
//
// Copyright Information: See EvtGen/BesCopyright
//      Copyright (A) 2006      Ping Rong-Gang @IHEP
//
// Module:  EvtRhoPi.cc
//
// Description: Jpsi or psi(2S) decays into 3 pions via rho(1--)pi
//
// Modification history:
//
//    Ping R.-G.       Apr., 2007       Module created
//
//------------------------------------------------------------------------
 
#include "EvtRhoPi.hh"
#include "../EvtGenBase/EvtDiracParticle.hh"
#include "../EvtGenBase/EvtGenKine.hh"
#include "../EvtGenBase/EvtHighSpinParticle.hh"
#include "../EvtGenBase/EvtNeutrinoParticle.hh"
#include "../EvtGenBase/EvtPDL.hh"
#include "../EvtGenBase/EvtParticle.hh"
#include "../EvtGenBase/EvtPatches.hh"
#include "../EvtGenBase/EvtPhotonParticle.hh"
#include "../EvtGenBase/EvtRandom.hh"
#include "../EvtGenBase/EvtRaritaSchwingerParticle.hh"
#include "../EvtGenBase/EvtReport.hh"
#include "../EvtGenBase/EvtScalarParticle.hh"
#include "../EvtGenBase/EvtStringParticle.hh"
#include "../EvtGenBase/EvtTensor4C.hh"
#include "../EvtGenBase/EvtTensorParticle.hh"
#include "../EvtGenBase/EvtVector4C.hh"
#include "../EvtGenBase/EvtVector4R.hh"
#include "../EvtGenBase/EvtVectorParticle.hh"
#include "EvtVVS.hh"
#include <stdlib.h>
#include <string>
using namespace std; //::endl;
 
EvtRhoPi::~EvtRhoPi() {}
 
void EvtRhoPi::getName( std::string& model_name ) { model_name = "RhoPi"; }
 
EvtDecayBase* EvtRhoPi::clone() { return new EvtRhoPi; }
 
void EvtRhoPi::init() {
 
  //  checkNArg(6);
  EvtSpinType::spintype parenttype = EvtPDL::getSpinType( getParentId() );
  //  if ( parenttype == EvtSpinType::SCALAR ){
  //  report(ERROR,"EvtGen")<<"Scalar decays with flat distribution"<<endl;
  //  ::abort();
  // }
}
void EvtRhoPi::initProbMax() { noProbMax(); }
 
static int    nrun     = 1;
static double max_amps = 0.0;
 
void EvtRhoPi::decay( EvtParticle* p ) {
 
  ///// default use rho(770) as the intermediate state, this set parameter will generate the
  /// symmetric momentum distribution for pi+ pi-.
  double ResonanceMass  = 0.7710;
  double ResonanceWidth = 0.1492;
  double r1             = 0.9;
  double phase1         = 0;
  double r2             = 1.1;
  double phase2         = 1.5;
  if ( getNArg() > 0 )
  {
    ResonanceMass  = getArg( 0 );
    ResonanceWidth = getArg( 1 );
    r1             = getArg( 2 );
    phase1         = getArg( 3 );
    r2             = getArg( 4 );
    phase2         = getArg( 5 );
  }
  double amps, SamAmps, rd1;
  // calculated the max amplitude square in 20000 events, is it enough larger?
  if ( nrun == 1 )
  {
    int ir, nd;
    for ( ir = 0; ir <= 20000; ir++ )
    {
      p->initializePhaseSpace( getNDaug(), getDaugs() );
      int nd = p->getNDaug(), i;
      _nd    = nd;
      for ( i = 0; i <= nd - 1; i++ )
      {
        _p4Lab[i] = p->getDaug( i )->getP4Lab();
        _p4CM[i]  = p->getDaug( i )->getP4();
      }
      amps = AmplitudeSquare( ResonanceMass, ResonanceWidth, r1, r2, phase1, phase2 );
      if ( amps > max_amps ) max_amps = amps * 1.01;
      nrun++;
    }
  }
  if ( max_amps == 0.0 )
  {
    report( ERROR, "EvtGen" ) << "The decay amplitude square should be positive number"
                              << endl;
    abort();
  }
  // cout<<"max_amp="<<max_amps<<endl;
 
loop:
  p->initializePhaseSpace( getNDaug(), getDaugs() );
  int i;
  for ( i = 0; i <= p->getNDaug() - 1; i++ )
  {
    _p4Lab[i] = p->getDaug( i )->getP4Lab();
    _p4CM[i]  = p->getDaug( i )->getP4();
  }
  //  Put phase space results into the daughters.
  amps    = AmplitudeSquare( ResonanceMass, ResonanceWidth, r1, r2, phase1, phase2 );
  SamAmps = amps / max_amps;
  rd1     = EvtRandom::Flat( 0.0, 1.0 );
  if ( rd1 >= SamAmps ) goto loop;
  return;
}
 
double EvtRhoPi::AmplitudeSquare( double ResonanceMass, double ResonanceWidth, double r1,
                                  double r2, double phase1, double phase2 ) {
  EvtVector4R dp1 = GetDaugMomLab( 0 );
  EvtVector4R dp2 = GetDaugMomLab( 1 );
  EvtVector4R dp3 = GetDaugMomLab( 2 );
  VVS Jpsi2rhopi( dp1, dp2, dp3, ResonanceMass, ResonanceWidth, r1, r2, phase1, phase2 );
  return Jpsi2rhopi.amps();
}