Sigma2qqbar2emu.cxx

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/*
  Copyright (C) 2002-2017 CERN for the benefit of the ATLAS collaboration
*/

 
#include "Pythia8_i/UserProcessFactory.h"
 
// calls to fortran routines
#include "CLHEP/Random/RandFlat.h"
 
#include <iostream>
#include <vector>
 
namespace Pythia8{
  class Sigma2qqbar2emu;
}
 
// This one line registers this process with the factory
// An instance of this process can be created with 
// UserProcessFactory::create("qqbar2emu")
Pythia8_UserProcess::UserProcessFactory::Creator<Pythia8::Sigma2qqbar2emu> qqbar2emuCreator("qqbar2emu");
 
namespace Pythia8 {
  
  
  class Sigma2qqbar2emu : public Sigma2Process{
    
  public:
    //Constructor.
    Sigma2qqbar2emu()
    : m_lambdaCoup(0.), m_sigmaTemp(0.), m_stop(0.),
    m_lambdaSqddbar(0.), m_lambdaSqdsbar(0.), m_lambdaSqsdbar(0.), m_lambdaSqssbar(0.),
    m_Nc(0), m_myRand(0) 
    {}
    
    
    void initProc() {
      
      // Store parameters.
      m_lambdaCoup = 0.2;
      m_Nc = 3;
      m_stop = particleDataPtr->m0(1000006);   //95.5;
      m_lambdaSqddbar = 0.065;
      m_lambdaSqdsbar = 3.8e-5;
      m_lambdaSqsdbar = 3.8e-5;
      m_lambdaSqssbar = 0.065;
      m_myRand = new Rndm(1234567);
      
      return;
    } 
    
    //*********
    
    void sigmaKin() {
      
      // The 2 out front is for e- mu+ plus e+ mu -
      m_sigmaTemp = 2./((float)m_Nc * 64. * M_PI);
      
      return;
    }
    
    //*********
    
    double sigmaHat() {
      
      double lambdaSq = 0.;
      if((id1 == 1 && id2 == -1) || (id1 == -1 && id2 == 1)) lambdaSq = m_lambdaSqddbar;
      else if((id1 == 1 && id2 == -3) || (id1 == -3 && id2 == 1)) lambdaSq = m_lambdaSqdsbar;
      else if((id1 == 3 && id2 == -1) || (id1 == -1 && id2 == 3)) lambdaSq = m_lambdaSqsdbar;
      else if((id1 == 3 && id2 == -3) || (id1 == -3 && id2 == 3)) lambdaSq = m_lambdaSqssbar;
      double sigma = pow2(lambdaSq)*m_sigmaTemp*tH2/(sH2*pow2(tH-pow2(m_stop)));
      return sigma;
    }
    
    //*********
    
    // Select identity, colour and anticolour.
    
    void setIdColAcol() {
      
      // Flavours.
      double x = m_myRand->flat();
      if(x < 0.5) setId( id1, id2, 11, -13);
      else setId( id1, id2, -11, 13);
      
      // tH defined between f and LQ: must swap tHat <-> uHat if qbar q in.
      swapTU = (id1 < 0); 
      
      //cab I don't understand what's done here.
      // Colour flow topologies.
      if (id1 > 0) setColAcol( 1, 0, 0, 1, 0, 0, 0, 0);
      else         setColAcol( 0, 1, 1, 0, 0, 0, 0, 0);
      
      return;
    }
    
    // Info on the subprocess.
    std::string name()    const {return "q qbar -> e mu (t:squark)";}
    //cab Need Codes for q qbar -> e+- mu-+
    int    code()    const {return 10001;}
    std::string inFlux()  const {return "qq";}
    //cab It looks like here is where the final state is specified
    //cab electrons are +-11, muons are +-13
    int    id3Mass() const {return 11;}
    int    id4Mass() const {return 13;}
    
  private:
    
    // Parameters set at initialization or for current kinematics.
    double m_lambdaCoup, m_sigmaTemp, m_stop;
    double m_lambdaSqddbar, m_lambdaSqdsbar, m_lambdaSqsdbar, m_lambdaSqssbar;
    int m_Nc;
    Rndm* m_myRand;
  
  };
}