EvtTauGamMu.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) 2014      Ping Rong-Gang
//
// Module: EvtHypWK.hh
//
// Description:  To generate decay tau->gamma mu with uses' helicity amplitudes, it can be used
//  for the decay Fermion -> photon Fermion .
//
// Modification history:
//
//    Pang C.-Y., Ping R.-G.    Mar, 2007       Module created
//    Ping R.G. Apr. 2007  change to helicity amplitude method
//------------------------------------------------------------------------
//
#include "EvtTauGamMu.hh"
#include "../EvtGenBase/EvtDiracSpinor.hh"
#include "../EvtGenBase/EvtGenKine.hh"
#include "../EvtGenBase/EvtHelSys.hh"
#include "../EvtGenBase/EvtId.hh"
#include "../EvtGenBase/EvtPDL.hh"
#include "../EvtGenBase/EvtParticle.hh"
#include "../EvtGenBase/EvtPatches.hh"
#include "../EvtGenBase/EvtReport.hh"
#include "../EvtGenBase/EvtVector4C.hh"
#include "../EvtGenBase/EvtdFunction.hh"
#include <iostream>
#include <stdlib.h>
#include <string>
 
using std::cout;
using std::endl;
 
EvtTauGamMu::~EvtTauGamMu() {}
 
void EvtTauGamMu::getName( std::string& model_name ) { model_name = "TauGamMu"; }
 
EvtDecayBase* EvtTauGamMu::clone() { return new EvtTauGamMu; }
 
void EvtTauGamMu::init() {
 
  // check that there are 0 arguments
  checkNArg( 4 );
  checkNDaug( 2 );
 
  checkSpinParent( EvtSpinType::DIRAC );
 
  checkSpinDaughter( 0, EvtSpinType::PHOTON );
  checkSpinDaughter( 1, EvtSpinType::DIRAC );
 
  for ( int i = 0; i <= 1; i++ )
  {
    for ( int j = 0; j <= 2; j++ )
    {
      for ( int k = 0; k <= 1; k++ ) { vertex( i, j, k, 0 ); }
    }
  }
 
  //---
}
 
void EvtTauGamMu::decay( EvtParticle* p ) {
 
  p->initializePhaseSpace( getNDaug(), getDaugs() );
 
  EvtParticle *l1, *l2;
  l1               = p->getDaug( 0 );
  l2               = p->getDaug( 1 );
  EvtVector4R DRP4 = l1->getP4();   // photon
  EvtVector4R MEP4 = l2->getP4();   // Mu
  EvtVector4R PRP4 = p->getP4();    // Parent Momentum
  EvtHelSys   angles( PRP4, DRP4 ); // using helicity sys.angles
  double      tht = angles.getHelAng( 1 );
  double      ph  = angles.getHelAng( 2 );
  double      gmm = 0;
 
  double H00 = getArg( 0 ); // H(1,1/2) for photon , mu
  double A00 = getArg( 1 ); // phase angle for H00
  double H11 = getArg( 2 ); // H(-1,-1/2)
  double A11 = getArg( 3 ); // phase angle H11
 
  EvtComplex A000 = Djmn( 0.5, 0.5, 0.5, ph, tht, gmm ) * H00 * exp( A00 ); // for 1/2 -> 1 1/2
  EvtComplex A100 =
      Djmn( 0.5, -0.5, 0.5, ph, tht, gmm ) * H00 * exp( A00 ); // for -1/2 -> 1 1/2
  EvtComplex A021 = Djmn( 0.5, 0.5, -0.5, ph, tht, gmm ) * H11 * exp( A11 );  // 1/2->-1,-1/2
  EvtComplex A121 = Djmn( 0.5, -0.5, -0.5, ph, tht, gmm ) * H11 * exp( A11 ); // -1/2->-1,-1/2
 
  vertex( 0, 0, 0, A000 );
  vertex( 0, 1, 1, A021 );
  vertex( 1, 0, 0, A100 );
  vertex( 1, 1, 1, A121 );
 
  return;
}