EvtBsquark.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: EvtTauScalarnu.cc
//
// Description: The leptonic decay of the tau meson.
//              E.g., tau- -> e- nueb nut
//
// Modification history:
//
//    RYD       January 17, 1997       Module created
//
//------------------------------------------------------------------------
//
#include "EvtBsquark.hh"
#include "../EvtGenBase/EvtDiracParticle.hh"
#include "../EvtGenBase/EvtDiracSpinor.hh"
#include "../EvtGenBase/EvtGammaMatrix.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 <iostream>
#include <string>
 
EvtBsquark::~EvtBsquark() {}
 
void EvtBsquark::getName( std::string& model_name ) { model_name = "BSQUARK"; }
 
EvtDecayBase* EvtBsquark::clone() { return new EvtBsquark; }
 
void EvtBsquark::init() {
 
  // check that there are 5 arguments
  checkNArg( 5 );
}
 
void EvtBsquark::initProbMax() {
 
  // For now do not set a maximum.
 
  // SetProbMax(0.000000000005);
}
 
void EvtBsquark::decay( EvtParticle* p ) {
 
  static EvtId cquark     = EvtPDL::getId( "c" );
  static EvtId anticquark = EvtPDL::getId( "anti-c" );
 
  static EvtIdSet leptons( "e-", "mu-", "tau-" );
 
  p->initializePhaseSpace( getNDaug(), getDaugs() );
 
  int charge = 1;
 
  EvtParticle* lepton;
  lepton = p->getDaug( 1 );
  if ( leptons.contains( lepton->getId() ) ) { charge = -1; }
 
  EvtDiracParticle charmquark;
 
  // this is a very crude approximation...
  if ( charge == -1 ) { charmquark.init( cquark, p->getDaug( 0 )->getP4() ); }
  else { charmquark.init( anticquark, p->getDaug( 0 )->getP4() ); }
 
  EvtVector4R p4c = p->getDaug( 0 )->getP4();
 
  EvtVector4R p4sn = p->getDaug( 2 )->getP4();
 
  EvtVector4R p4b( p->mass(), 0.0, 0.0, 0.0 );
 
  EvtComplex M[2][2];
 
  int il, ic;
 
  // project out the right handed current
  EvtGammaMatrix PR = 0.5 * ( EvtGammaMatrix::id() + EvtGammaMatrix::g5() );
 
  double tanbeta = getArg( 1 );
  double cosbeta = cos( atan( tanbeta ) );
  double sinbeta = sin( atan( tanbeta ) );
 
  double mb = 4.9;
  double mc = 1.3;
  double mw = 80.4;
 
  double Mass      = getArg( 2 );
  double mu        = getArg( 3 );
  double mchargino = getArg( 4 );
 
  double tan2phim = 2 * sqrt( 2.0 ) * mw * ( mu * cosbeta + Mass * sinbeta ) /
                    ( Mass * Mass - mu * mu + 2 * mw * mw * cos( 2 * atan( tanbeta ) ) );
 
  double phim = 0.5 * atan( tan2phim );
 
  EvtComplex U11 = cos( phim );
  EvtComplex U12 = sin( phim );
  EvtComplex U21 = -sin( phim );
  EvtComplex U22 = cos( phim );
 
  double tan2phip = 2 * sqrt( 2.0 ) * mw * ( mu * cosbeta + Mass * sinbeta ) /
                    ( Mass * Mass - mu * mu - 2 * mw * mw * cos( 2 * atan( tanbeta ) ) );
 
  double phip = 0.5 * atan( tan2phip );
 
  EvtComplex V11 = cos( phip );
  EvtComplex V12 = sin( phip );
  EvtComplex V21 = -sin( phip );
  EvtComplex V22 = cos( phip );
 
  double theta  = getArg( 0 );
  double ctheta = cos( theta );
  double stheta = sin( theta );
 
  double vcsb  = 0.08;
  double mchi1 = mchargino;
  double mchi2 = mchargino;
 
  // overall scale factor
  double g = 1.0;
 
  EvtComplex a1 =
      mchi1 * ( U11 * ctheta - mb * U12 * stheta / ( sqrt( 2.0 ) * mw * cosbeta ) );
  EvtComplex a2 =
      mchi2 * ( U21 * ctheta - mb * U22 * stheta / ( sqrt( 2.0 ) * mw * cosbeta ) );
 
  EvtComplex b1 = mc * conj( V12 ) * ctheta / ( sqrt( 2.0 ) * mw * sinbeta );
  EvtComplex b2 = mc * conj( V22 ) * ctheta / ( sqrt( 2.0 ) * mw * sinbeta );
 
  EvtComplex f1 = -( g * g * V11 * vcsb ) / ( ( p4b - p4c ).mass2() - mchi1 * mchi1 );
  EvtComplex f2 = -( g * g * V21 * vcsb ) / ( ( p4b - p4c ).mass2() - mchi1 * mchi2 );
 
  // report(INFO,"EvtGen") <<g<<" "<<V11<<" "<<FL<<" "<<vcsb<<" "<<mchi1<<endl;
  // report(INFO,"EvtGen") << "f1:"<<f1<<" "<<(p4b-p4c).mass2()<<endl;
  // report(INFO,"EvtGen") << "f2:"<<f2<<" "<<(p4b-p4c).mass2()<<endl;
 
  // report(INFO,"EvtGen") << "p4sn:"<<p4sn<<endl;
 
  EvtGammaMatrix pslash =
      p4sn.get( 0 ) * EvtGammaMatrix::g0() - p4sn.get( 1 ) * EvtGammaMatrix::g1() -
      p4sn.get( 2 ) * EvtGammaMatrix::g2() - p4sn.get( 3 ) * EvtGammaMatrix::g3();
 
  // report(INFO,"EvtGen") << "pslash:"<<pslash<<endl;
 
  for ( il = 0; il < 2; il++ )
  {
    for ( ic = 0; ic < 2; ic++ )
    {
 
      EvtComplex a = 0.0;
      EvtComplex b = 0.0;
 
      if ( charge == -1 )
      {
        a = charmquark.spParent( ic ) * ( PR * lepton->spParent( il ) );
        b = charmquark.spParent( ic ) * ( ( pslash * PR ) * lepton->spParent( il ) );
      }
      else
      {
        a = lepton->spParent( il ) * ( PR * charmquark.spParent( ic ) );
        b = lepton->spParent( il ) * ( ( pslash * PR ) * charmquark.spParent( ic ) );
      }
 
      // report(INFO,"EvtGen") <<"pslash*PR:"<<pslash*PR<<endl;
      // report(INFO,"EvtGen") <<"sp charm:"<<charmquark.spParent(ic)<<endl;
      // report(INFO,"EvtGen") <<"sp lepton:"<<lepton->spParent(il)<<endl;
 
      M[ic][il] = f1 * ( a1 * a + b1 * b ) + f2 * ( a2 * a + b2 * b );
 
      // report(INFO,"EvtGen") << "Contr1:"<<a1<<" "<<a<<" "<<b1<<" "<<b<<endl;
      // report(INFO,"EvtGen") << "Contr2:"<<a2<<" "<<a<<" "<<b2<<" "<<b<<endl;
 
      // report(INFO,"EvtGen") <<"case1:"<<f1<<" "<<a1<<" "<<b1<<" "<<a<<" "<<b<<endl;
      // report(INFO,"EvtGen") <<"case2:"<<f2<<" "<<a2<<" "<<b2<<" "<<a<<" "<<b<<endl;
    }
  }
 
  double prob = real( M[0][0] * conj( M[0][0] ) + M[1][0] * conj( M[1][0] ) +
                      M[0][1] * conj( M[0][1] ) + M[1][1] * conj( M[1][1] ) );
 
  // report(INFO,"EvtGen") <<"prob:"<<prob<<endl;
 
  setProb( prob );
 
  return;
}