Pythia8::PTRelVetoedShower Class Reference

This user hook is derived from the main31 example distributed with Pythia 8 and is for use with QCD events generated with PoWHEG. More...

Inheritance diagram for Pythia8::PTRelVetoedShower:

Collaboration diagram for Pythia8::PTRelVetoedShower:

Public Member Functions
	PTRelVetoedShower ()
	~PTRelVetoedShower ()
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 More...
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. More...
bool	doVetoFSREmission (int, const Event &evt, int iSys, bool)
	This is similar to the ISR veto. More...
bool	canVetoMPIStep ()
	Switch on calling of doVetoMPIStep. More...
int	numberVetoMPIStep ()
	Call doVetoMIStep once. More...
bool	canVetoISREmission ()
	Switch on veto of ISR. More...
bool	canVetoFSREmission ()
	Switch off veto of FSR. More...

Private Attributes
const size_t	m_nPoWHEGFinal
double	m_powhegScale
double	m_pxCMS
double	m_pyCMS
double	m_pzCMS

Detailed Description

This user hook is derived from the main31 example distributed with Pythia 8 and is for use with QCD events generated with PoWHEG.

The following settings must be used 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.

One key difference between this veto and the one implemented in main31 is the determination of the boost to the CMS frame in which the FSR veto is tested. In main31, that boost is determined on each shower emission, with the result that it evolves due to recoil of the incoming partons against ISR. In this veto, the boost is determined once in each event and does not evolve with recoil

Definition at line 35 of file PTRelVetoedShower.cxx.

Constructor & Destructor Documentation

PTRelVetoedShower()

Pythia8::PTRelVetoedShower::PTRelVetoedShower ( )

inline

Definition at line 39 of file PTRelVetoedShower.cxx.

                       : m_nPoWHEGFinal(2), m_powhegScale(0.){
      
      std::cout<<"*************************************************************************"<<std::endl;
      std::cout<<"*                                                                       *"<<std::endl;
      std::cout<<"*        Using PTRel vetoed shower for PoWHEG QCD production!           *"<<std::endl;
      std::cout<<"*                                                                       *"<<std::endl;
      std::cout<<"*************************************************************************"<<std::endl;
 
      m_pxCMS = 0;
      m_pyCMS = 0;
      m_pzCMS = 0;
      
    }

~PTRelVetoedShower()

Pythia8::PTRelVetoedShower::~PTRelVetoedShower ( )

inline

Definition at line 53 of file PTRelVetoedShower.cxx.

{}

Member Function Documentation

canVetoFSREmission()

bool Pythia8::PTRelVetoedShower::canVetoFSREmission ( )

inline

Switch off veto of FSR.

Definition at line 203 of file PTRelVetoedShower.cxx.

{return true;}

canVetoISREmission()

bool Pythia8::PTRelVetoedShower::canVetoISREmission ( )

inline

Switch on veto of ISR.

Definition at line 201 of file PTRelVetoedShower.cxx.

{return true;}

canVetoMPIStep()

bool Pythia8::PTRelVetoedShower::canVetoMPIStep ( )

inline

Switch on calling of doVetoMPIStep.

Definition at line 197 of file PTRelVetoedShower.cxx.

{return true;}

doVetoFSREmission()

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

inline

This is similar to the ISR veto.

Definition at line 177 of file PTRelVetoedShower.cxx.

                                                                 {
      if(iSys != 0) return false;
      
      size_t emissionIndex = Pythia8_UserHooks::findLastFSREmission(evt);
      size_t radiatorIndex = Pythia8_UserHooks::findLastFSRRadiator(evt);
      
      Particle emission(evt[emissionIndex]);
      Particle radiator(evt[radiatorIndex]);
      
      emission.bst(m_pxCMS, m_pyCMS, m_pzCMS);
      radiator.bst(m_pxCMS, m_pyCMS, m_pzCMS);
      
      double pTRel = Pythia8_UserHooks::pTLeg(emission, radiator);
      if(pTRel > m_powhegScale) return true;
      
      return false;
    }

doVetoISREmission()

bool Pythia8::PTRelVetoedShower::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 161 of file PTRelVetoedShower.cxx.

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

doVetoMPIStep()

bool Pythia8::PTRelVetoedShower::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 61 of file PTRelVetoedShower.cxx.

                                                  {
      
      // Only do anything on the first call.
      if(nMPI > 1) return false;
      
      m_powhegScale = infoPtr->QRen();
 
      size_t nPwgOutgoing = 0;
      
      for(int ii = evt.size()-1; ii > 0; --ii){
        if(! (evt[ii].isFinal())) break;
        ++nPwgOutgoing;
      }
      
      if(nPwgOutgoing == m_nPoWHEGFinal) return false;
      
      if(nPwgOutgoing != m_nPoWHEGFinal + 1){
        throw std::runtime_error("Wrong number of final state PoWHEG legs: " + std::to_string(nPwgOutgoing));
      }
      
      // momentum components to boost to CMS frame
      m_pxCMS = 0.;
      m_pyCMS = 0.;
      m_pzCMS = 0.;
      double eCMS  = 0.;
      
      // The outgoing powheg legs
      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){
          m_pxCMS += evt[ii].px();
          m_pyCMS += evt[ii].py();
          m_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]));
        }
      }
      
      // Start the search for the powheg scale above the collision energy, 
      // which is guaranteed to be above the veto scale.
      
      m_powhegScale = 1.1*infoPtr->s();
      
      // compare the pT of each leg to the powheg scale.
      // Set the scale to the lowest
      for(std::vector<Particle>::const_iterator leg=powhegLegs.begin();
          leg != powhegLegs.end(); ++leg){
        double pTTmp = leg->pT();
        if(pTTmp < m_powhegScale )m_powhegScale = pTTmp;
      }
      
      // normalise the boost vector to the CMS frame...
      double norm = -1./eCMS;
      m_pxCMS *= norm;
      m_pyCMS *= norm;
      m_pzCMS *= norm;
      
      // ...and boost all outgoing legs to that frame
      for(std::vector<Particle>::iterator leg=powhegLegs.begin();
          leg != powhegLegs.end(); ++leg){
        leg->bst(m_pxCMS, m_pyCMS, m_pzCMS);
      }
      
      for(std::vector<Particle>::const_iterator leg=powhegLegs.begin();
          leg != powhegLegs.end(); ++leg){
        // 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;
        }
      }
      
      // barf if the scale was not found properly!
      if(m_powhegScale > infoPtr->s()){
        throw std::runtime_error("Veto scale could not be determined!");
      }
      
      return false;
    }

numberVetoMPIStep()

int Pythia8::PTRelVetoedShower::numberVetoMPIStep ( )

inline

Call doVetoMIStep once.

Definition at line 199 of file PTRelVetoedShower.cxx.

{return 1;}

Member Data Documentation

m_nPoWHEGFinal

const size_t Pythia8::PTRelVetoedShower::m_nPoWHEGFinal

private

Definition at line 207 of file PTRelVetoedShower.cxx.

m_powhegScale

double Pythia8::PTRelVetoedShower::m_powhegScale

private

Definition at line 209 of file PTRelVetoedShower.cxx.

m_pxCMS

double Pythia8::PTRelVetoedShower::m_pxCMS

private

Definition at line 212 of file PTRelVetoedShower.cxx.

m_pyCMS

double Pythia8::PTRelVetoedShower::m_pyCMS

private

Definition at line 213 of file PTRelVetoedShower.cxx.

m_pzCMS

double Pythia8::PTRelVetoedShower::m_pzCMS

private

Definition at line 214 of file PTRelVetoedShower.cxx.

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

• PTRelVetoedShower.cxx