QCDVetoedShower.cxx

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/*
  Copyright (C) 2002-2017 CERN for the benefit of the ATLAS collaboration
*/
 
#include "UserHooksUtils.h"
#include "Pythia8_i/UserHooksFactory.h"
#include <stdexcept>
#include <iostream>
 
namespace Pythia8{
  class QCDVetoedShower;
}
 
Pythia8_UserHooks::UserHooksFactory::Creator<Pythia8::QCDVetoedShower> qcdVetoedShowerCreator("QCDVetoedShower");
 
namespace Pythia8{

  class QCDVetoedShower : public UserHooks{
 
  public:
 
    QCDVetoedShower(): m_powhegScale(0.){
 
      std::cout<<"*******************************************************************"<<std::endl;
      std::cout<<"*                                                                 *"<<std::endl;
      std::cout<<"*        Using vetoed shower for PoWHEG QCD production!           *"<<std::endl;
      std::cout<<"*                                                                 *"<<std::endl;
      std::cout<<"*******************************************************************"<<std::endl;
      
    }
 
    ~QCDVetoedShower(){}

    bool doVetoMPIStep(int nMPI, const Event &evt){
 
      // Only do anything on the first call.
      if(nMPI > 1) return false;
      
      m_powhegScale = infoPtr->QRen();
            
      m_powhegLegs.clear();
      // start the loop at 1, since entry 0 represents the event as a whole
      for(int ii=1; ii != evt.size(); ++ii){
        // here Event::isFinal refers to whether the particle can still decay/radiate, or whether it is an internal leg
        if(evt[ii].isFinal()){
          m_powhegLegs.push_back(ii);
        }
      }
      
      return false;
    }

    bool doVetoISREmission(int, const Event &evt, int iSys){
 
      // only veto emissions from the hard system
      if(iSys != 0) return false;
      
      size_t emission = Pythia8_UserHooks::findLastISREmission(evt);
 
      return checkEmission(emission, evt);
 
    }
    
    bool doVetoFSREmission(int, const Event &evt, int iSys, bool){
 
      // only veto emissions from the hard system
      if(iSys != 0) return false;
      
      size_t emission = Pythia8_UserHooks::findLastFSREmission(evt);
 
      return checkEmission(emission, evt);
    }

    bool canVetoMPIStep(){return true;}
    int numberVetoMPIStep(){return 1;}
    bool canVetoISREmission(){return true;}
    bool canVetoFSREmission(){return true;}
 
  private:
    
    bool checkEmission(size_t emission, const Event &evt){
      // Veto if above the POWHEG scale
      if (evt[emission].pT() > m_powhegScale) return true;
      
      // determine pT relative to each outgoing PoWHEG leg and veto if above veto scale
            
      for(std::vector<size_t>::const_iterator legIndex = m_powhegLegs.begin();
          legIndex != m_powhegLegs.end(); ++legIndex){
        
        if(Pythia8_UserHooks::pTLeg(emission, *legIndex, evt) > m_powhegScale)return true;
      }
      return false;
    }
    
    double m_powhegScale;
    // Indices of the PoWHEG legs in the event record
    std::vector<size_t> m_powhegLegs;
  };
}