Pythia8::PoWHEGVetoedShower Class Reference

This UserHook should be used when showering QCD jets generated with PoWHEG-box. More...

Inheritance diagram for Pythia8::PoWHEGVetoedShower:

Collaboration diagram for Pythia8::PoWHEGVetoedShower:

Public Member Functions
	PoWHEGVetoedShower ()
	~PoWHEGVetoedShower ()
bool	doVetoMPIStep (int nMPI, const Event &evt)
	doVetoMPIStep is called immediately after the MPI generation In this case it never actually vetoes the MPI, but since it is called before the ISR veto check this is a convenient place to find the PoWHEG scale from the LHEF event
bool	doVetoISREmission (int, const Event &evt, int iSys)
	This is called after the generation of each new ISR emission Can use it to test if the last generated emission is above the veto scale.
bool	doVetoFSREmission (int, const Event &evt, int iSys, bool)
	This is similar to the ISR veto.
bool	canVetoMPIStep ()
	Switch on calling of doVetoMPIStep.
int	numberVetoMPIStep ()
	Call doVetoMIStep once.
bool	canVetoISREmission ()
	Switch on veto of ISR.
bool	canVetoFSREmission ()
	Switch off veto of FSR.

Private Attributes
double	m_powhegScale

Detailed Description

This UserHook should be used when showering QCD jets generated with PoWHEG-box.

The following settings must be activated in Pythia:

SpaceShower:pTMaxMatch = 2 TimeShower:pTMaxMatch = 2

These set the limit for emission from both initial and final state radiation to the kinematic (beam) energy. The veto hook then vetos any emission that would be above the appropriate scale.

This Hook determines a new (lower) veto scale according to the following prescription: Compute the pT of every PoWHEG leg relative to the beam, and the pT of every outgoing PoWHEG leg relative to all the other legs in the CMS frame. Use the lowest of these values as the new veto scale

This hook is ONLY SUITABLE FOR QCD JET PRODUCTION!!

Definition at line 34 of file PoWHEGVetoedShower.cxx.

Constructor & Destructor Documentation

PoWHEGVetoedShower()

Pythia8::PoWHEGVetoedShower::PoWHEGVetoedShower ( )

inline

Definition at line 38 of file PoWHEGVetoedShower.cxx.

                        : m_powhegScale(0.){
 
      std::cout<<"*******************************************************************"<<std::endl;
      std::cout<<"*                                                                 *"<<std::endl;
      std::cout<<"*  Using new PoWHEG author scale definition for QCD production!   *"<<std::endl;
      std::cout<<"*                                                                 *"<<std::endl;
      std::cout<<"*******************************************************************"<<std::endl;
      
    }

~PoWHEGVetoedShower()

Pythia8::PoWHEGVetoedShower::~PoWHEGVetoedShower ( )

inline

Definition at line 48 of file PoWHEGVetoedShower.cxx.

{}

Member Function Documentation

canVetoFSREmission()

bool Pythia8::PoWHEGVetoedShower::canVetoFSREmission ( )

inline

Switch off veto of FSR.

Definition at line 172 of file PoWHEGVetoedShower.cxx.

{return true;}

canVetoISREmission()

bool Pythia8::PoWHEGVetoedShower::canVetoISREmission ( )

inline

Switch on veto of ISR.

Definition at line 170 of file PoWHEGVetoedShower.cxx.

{return true;}

canVetoMPIStep()

bool Pythia8::PoWHEGVetoedShower::canVetoMPIStep ( )

inline

Switch on calling of doVetoMPIStep.

Definition at line 166 of file PoWHEGVetoedShower.cxx.

{return true;}

doVetoFSREmission()

bool Pythia8::PoWHEGVetoedShower::doVetoFSREmission ( int , const Event & evt, int iSys, bool  )

inline

This is similar to the ISR veto.

Definition at line 152 of file PoWHEGVetoedShower.cxx.

                                                                 {
 
      // only veto emissions from the hard system
      if(iSys != 0) return false;
      
      size_t emission = Pythia8_UserHooks::findLastFSREmission(evt);
 
      // Veto if above the POWHEG scale
      if (evt[emission].pT() > m_powhegScale) return true;
      
      return false;
    }

doVetoISREmission()

bool Pythia8::PoWHEGVetoedShower::doVetoISREmission ( int , const Event & evt, int iSys )

inline

This is called after the generation of each new ISR emission Can use it to test if the last generated emission is above the veto scale.

Definition at line 136 of file PoWHEGVetoedShower.cxx.

                                                           {
 
      // only veto emissions from the hard system
      if(iSys != 0) return false;
      
      size_t emission = Pythia8_UserHooks::findLastISREmission(evt);
 
      // Veto emission above the veto scale
      if(evt[emission].pT() > m_powhegScale) return true;
      
      return false;
    }

doVetoMPIStep()

bool Pythia8::PoWHEGVetoedShower::doVetoMPIStep ( int nMPI, const Event & evt )

inline

doVetoMPIStep is called immediately after the MPI generation In this case it never actually vetoes the MPI, but since it is called before the ISR veto check this is a convenient place to find the PoWHEG scale from the LHEF event

Definition at line 56 of file PoWHEGVetoedShower.cxx.

                                                  {
 
      // Only do anything on the first call.
      if(nMPI > 1) return false;
      
      m_powhegScale = infoPtr->QRen();;
      
      // momentum components to boost to CMS frame
      double pxCMS = 0.;
      double pyCMS = 0.;
      double pzCMS = 0.;
      double eCMS  = 0.;
      
      std::vector<Particle> powhegLegs;
      
      // Find the entries corresponding to outgoing legs from PoWHEG
      // start the loop at 1, since entry 0 represents the event as a whole
      for(int ii=1; ii != evt.size(); ++ii){
 
        // status -21 is the incoming hard partons
        if(evt[ii].status() == -21){
          pxCMS += evt[ii].px();
          pyCMS += evt[ii].py();
          pzCMS += evt[ii].pz();   
          eCMS  += evt[ii].e();
        }
        
        // here Event::isFinal refers to whether the particle can still decay/radiate, or whether it is an internal leg
        if(evt[ii].isFinal()){
          powhegLegs.push_back(Particle(evt[ii]));
        }
      }
      
      // compare the pT of each leg to the powheg scale.
      // Set the scale to the lowest (or leave the scale unchanged if it is already lower)
      for(std::vector<Particle>::const_iterator leg=powhegLegs.begin();
          leg != powhegLegs.end(); ++leg){
        if(leg->pT() < m_powhegScale )m_powhegScale = leg->pT();
      }
      
      double norm = -1./eCMS;
      pxCMS *= norm;
      pyCMS *= norm;
      pzCMS *= norm;
      
      // boost all outgoing legs to the CMS frame
      for(std::vector<Particle>::iterator leg=powhegLegs.begin();
          leg != powhegLegs.end(); ++leg){
        leg->bst(pxCMS, pyCMS, pzCMS);
      }
      
      for(std::vector<Particle>::const_iterator leg=powhegLegs.begin();
          leg != powhegLegs.end(); ++leg){
        
        if(leg->pT() < m_powhegScale )m_powhegScale = leg->pT();
        
        // calculate the pT relative to each other leg 
        // if any such pT is lower than the current scale, reset the scale to that value
        for(std::vector<Particle>::const_iterator otherLeg = powhegLegs.begin();
            otherLeg != powhegLegs.end(); ++otherLeg){
          if(otherLeg == leg) continue;
          
          double pTLeg = Pythia8_UserHooks::pTLeg(*leg, *otherLeg);
 
          if(pTLeg < m_powhegScale) m_powhegScale = pTLeg;
        }
      }
 
//      std::cout<<m_powhegScale<<"  "<<infoPtr->QRen()<<std::endl;
 
      
      return false;
    }

numberVetoMPIStep()

int Pythia8::PoWHEGVetoedShower::numberVetoMPIStep ( )

inline

Call doVetoMIStep once.

Definition at line 168 of file PoWHEGVetoedShower.cxx.

{return 1;}

Member Data Documentation

m_powhegScale

double Pythia8::PoWHEGVetoedShower::m_powhegScale

private

Definition at line 176 of file PoWHEGVetoedShower.cxx.

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The documentation for this class was generated from the following file:

• PoWHEGVetoedShower.cxx