EvtTauHadnu.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: EvtTauHadnu.cc
//
// Description: The leptonic decay of the tau meson.
//              E.g., tau- -> e- nueb nut
//
// Modification history:
//
//    RYD       January 17, 1997       Module created
//
//------------------------------------------------------------------------
//
#include "EvtTauHadnu.hh"
#include "../EvtGenBase/EvtDiracSpinor.hh"
#include "../EvtGenBase/EvtGenKine.hh"
#include "../EvtGenBase/EvtIdSet.hh"
#include "../EvtGenBase/EvtPDL.hh"
#include "../EvtGenBase/EvtParticle.hh"
#include "../EvtGenBase/EvtPatches.hh"
#include "../EvtGenBase/EvtReport.hh"
#include "../EvtGenBase/EvtVector4C.hh"
#include <iostream>
#include <stdlib.h>
#include <string>
using std::endl;
 
EvtTauHadnu::~EvtTauHadnu() {}
 
void EvtTauHadnu::getName( std::string& model_name ) { model_name = "TAUHADNU"; }
 
EvtDecayBase* EvtTauHadnu::clone() { return new EvtTauHadnu; }
 
void EvtTauHadnu::init() {
 
  // check that there are 0 arguments
 
  checkSpinParent( EvtSpinType::DIRAC );
 
  // the last daughter should be a neutrino
  checkSpinDaughter( getNDaug() - 1, EvtSpinType::NEUTRINO );
 
  int i;
  for ( i = 0; i < ( getNDaug() - 1 ); i++ ) { checkSpinDaughter( i, EvtSpinType::SCALAR ); }
 
  bool validndaug = false;
 
  if ( getNDaug() == 4 )
  {
    // pipinu
    validndaug = true;
    checkNArg( 7 );
    _beta       = getArg( 0 );
    _mRho       = getArg( 1 );
    _gammaRho   = getArg( 2 );
    _mRhopr     = getArg( 3 );
    _gammaRhopr = getArg( 4 );
    _mA1        = getArg( 5 );
    _gammaA1    = getArg( 6 );
  }
  if ( getNDaug() == 3 )
  {
    // pipinu
    validndaug = true;
    checkNArg( 5 );
    _beta       = getArg( 0 );
    _mRho       = getArg( 1 );
    _gammaRho   = getArg( 2 );
    _mRhopr     = getArg( 3 );
    _gammaRhopr = getArg( 4 );
  }
  if ( getNDaug() == 2 )
  {
    // pipinu
    validndaug = true;
    checkNArg( 0 );
  }
 
  if ( !validndaug )
  {
    report( ERROR, "EvtGen" ) << "Have not yet implemented this final state in TAUHADNU model"
                              << endl;
    report( ERROR, "EvtGen" ) << "Ndaug=" << getNDaug() << endl;
    int id;
    for ( id = 0; id < ( getNDaug() - 1 ); id++ )
      report( ERROR, "EvtGen" ) << "Daug " << id << " "
                                << EvtPDL::name( getDaug( id ) ).c_str() << endl;
  }
}
 
void EvtTauHadnu::initProbMax() {
 
  if ( getNDaug() == 2 ) setProbMax( 90.0 );
  if ( getNDaug() == 3 ) setProbMax( 2500.0 );
  if ( getNDaug() == 4 ) setProbMax( 5000.0 );
}
 
void EvtTauHadnu::decay( EvtParticle* p ) {
 
  static EvtId TAUM = EvtPDL::getId( "tau-" );
 
  EvtIdSet thePis( "pi+", "pi-", "pi0" );
  EvtIdSet theKs( "K+", "K-" );
 
  p->initializePhaseSpace( getNDaug(), getDaugs() );
 
  EvtParticle* nut;
  nut = p->getDaug( getNDaug() - 1 );
 
  // get the leptonic current
  EvtVector4C tau1, tau2;
 
  if ( p->getId() == TAUM )
  {
    tau1 = EvtLeptonVACurrent( nut->spParentNeutrino(), p->sp( 0 ) );
    tau2 = EvtLeptonVACurrent( nut->spParentNeutrino(), p->sp( 1 ) );
  }
  else
  {
    tau1 = EvtLeptonVACurrent( p->sp( 0 ), nut->spParentNeutrino() );
    tau2 = EvtLeptonVACurrent( p->sp( 1 ), nut->spParentNeutrino() );
  }
 
  EvtVector4C hadCurr;
  bool        foundHadCurr = false;
  if ( getNDaug() == 2 )
  {
    hadCurr      = p->getDaug( 0 )->getP4();
    foundHadCurr = true;
  }
  if ( getNDaug() == 3 )
  {
 
    // pi pi nu with rho and rhopr resonance
    if ( thePis.contains( getDaug( 0 ) ) && thePis.contains( getDaug( 1 ) ) )
    {
 
      EvtVector4R q1 = p->getDaug( 0 )->getP4();
      EvtVector4R q2 = p->getDaug( 1 )->getP4();
 
      hadCurr = Fpi( q1, q2 ) * ( q1 - q2 );
 
      foundHadCurr = true;
    }
  }
  if ( getNDaug() == 4 )
  {
    if ( thePis.contains( getDaug( 0 ) ) && thePis.contains( getDaug( 1 ) ) &&
         thePis.contains( getDaug( 2 ) ) )
    {
      foundHadCurr = true;
      // figure out which is the different charged pi
      // want it to be q3
 
      int diffPi( 0 ), samePi1( 0 ), samePi2( 0 );
      if ( getDaug( 0 ) == getDaug( 1 ) )
      {
        diffPi  = 2;
        samePi1 = 0;
        samePi2 = 1;
      }
      if ( getDaug( 0 ) == getDaug( 2 ) )
      {
        diffPi  = 1;
        samePi1 = 0;
        samePi2 = 2;
      }
      if ( getDaug( 1 ) == getDaug( 2 ) )
      {
        diffPi  = 0;
        samePi1 = 1;
        samePi2 = 2;
      }
 
      EvtVector4R q1 = p->getDaug( samePi1 )->getP4();
      EvtVector4R q2 = p->getDaug( samePi2 )->getP4();
      EvtVector4R q3 = p->getDaug( diffPi )->getP4();
 
      EvtVector4R Q      = q1 + q2 + q3;
      double      qMass2 = Q.mass2();
 
      double GA1 = _gammaA1 * pi3G( Q.mass2(), samePi1 ) / pi3G( _mA1 * _mA1, samePi1 );
 
      EvtComplex denBA1( _mA1 * _mA1 - Q.mass2(), -1. * _mA1 * GA1 );
      EvtComplex BA1 = _mA1 * _mA1 / denBA1;
 
      hadCurr = BA1 * ( ( q1 - q3 ) - ( Q * ( Q * ( q1 - q3 ) ) / qMass2 ) * Fpi( q2, q3 ) +
                        ( q2 - q3 ) - ( Q * ( Q * ( q2 - q3 ) ) / qMass2 ) * Fpi( q1, q3 ) );
    }
  }
 
  if ( !foundHadCurr )
  {
    report( ERROR, "EvtGen" ) << "Have not yet implemented this final state in TAUHADNU model"
                              << endl;
    report( ERROR, "EvtGen" ) << "Ndaug=" << getNDaug() << endl;
    int id;
    for ( id = 0; id < ( getNDaug() - 1 ); id++ )
      report( ERROR, "EvtGen" ) << "Daug " << id << " "
                                << EvtPDL::name( getDaug( id ) ).c_str() << endl;
  }
 
  vertex( 0, tau1 * hadCurr );
  vertex( 1, tau2 * hadCurr );
 
  return;
}
 
double EvtTauHadnu::pi3G( double m2, int dupD ) {
  double mPi = EvtPDL::getMeanMass( getDaug( dupD ) );
  if ( m2 > ( _mRho + mPi ) )
  { return m2 * ( 1.623 + 10.38 / m2 - 9.32 / ( m2 * m2 ) + 0.65 / ( m2 * m2 * m2 ) ); }
  else
  {
    double t1 = m2 - 9.0 * mPi * mPi;
    return 4.1 * pow( t1, 3.0 ) * ( 1.0 - 3.3 * t1 + 5.8 * t1 * t1 );
  }
  return 0.;
}
 
EvtComplex EvtTauHadnu::Fpi( EvtVector4R q1, EvtVector4R q2 ) {
 
  double m1 = q1.mass();
  double m2 = q2.mass();
 
  EvtVector4R Q   = q1 + q2;
  double      mQ2 = Q * Q;
 
  // momenta in the rho->pipi decay
  double dRho   = _mRho * _mRho - m1 * m1 - m2 * m2;
  double pPiRho = ( 1.0 / _mRho ) * sqrt( ( dRho * dRho ) / 4.0 - m1 * m1 * m2 * m2 );
 
  double dRhopr   = _mRhopr * _mRhopr - m1 * m1 - m2 * m2;
  double pPiRhopr = ( 1.0 / _mRhopr ) * sqrt( ( dRhopr * dRhopr ) / 4.0 - m1 * m1 * m2 * m2 );
 
  double dQ   = mQ2 - m1 * m1 - m2 * m2;
  double pPiQ = ( 1.0 / sqrt( mQ2 ) ) * sqrt( ( dQ * dQ ) / 4.0 - m1 * m1 * m2 * m2 );
 
  double     gammaRho = _gammaRho * _mRho / sqrt( mQ2 ) * pow( ( pPiQ / pPiRho ), 3 );
  EvtComplex BRhoDem( _mRho * _mRho - mQ2, -1.0 * _mRho * gammaRho );
  EvtComplex BRho = _mRho * _mRho / BRhoDem;
 
  double     gammaRhopr = _gammaRhopr * _mRhopr / sqrt( mQ2 ) * pow( ( pPiQ / pPiRhopr ), 3 );
  EvtComplex BRhoprDem( _mRhopr * _mRhopr - mQ2, -1.0 * _mRho * gammaRhopr );
  EvtComplex BRhopr = _mRhopr * _mRhopr / BRhoprDem;
 
  return ( BRho + _beta * BRhopr ) / ( 1 + _beta );
}