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 "EvtGenBase/EvtPatches.hh"
#include "EvtGenBase/EvtPatches.hh"
#include <iostream>
#include <string>
#include "EvtGenBase/EvtParticle.hh"
#include "EvtGenBase/EvtDiracParticle.hh"
#include "EvtGenBase/EvtPDL.hh"
#include "EvtGenBase/EvtIdSet.hh"
#include "EvtGenBase/EvtGenKine.hh"
#include "EvtGenModels/EvtBsquark.hh"
#include "EvtGenBase/EvtDiracSpinor.hh"
#include "EvtGenBase/EvtGammaMatrix.hh"
#include "EvtGenBase/EvtReport.hh"
 
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;
 
}