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// main83.cc is a part of the PYTHIA event generator.
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// Copyright (C) 2012 Torbjorn Sjostrand.
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// PYTHIA is licenced under the GNU GPL version 2, see COPYING for details.
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// Please respect the MCnet Guidelines, see GUIDELINES for details.
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// This program is written by Stefan Prestel.
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// It illustrates how to do CKKW-L merging,
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// see the Matrix Element Merging page in the online manual.
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using namespace Pythia8;
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// Functions for histogramming
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#include "fastjet/PseudoJet.hh"
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#include "fastjet/ClusterSequence.hh"
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#include "fastjet/CDFMidPointPlugin.hh"
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#include "fastjet/CDFJetCluPlugin.hh"
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#include "fastjet/D0RunIIConePlugin.hh"
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//==========================================================================
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// Find the Durham kT separation of the clustering from
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// nJetMin --> nJetMin-1 jets in te input event
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double pTfirstJet( const Event& event, int nJetMin, double Rparam) {
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double yPartonMax = 4.;
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// Fastjet analysis - select algorithm and parameters
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fastjet::Strategy strategy = fastjet::Best;
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fastjet::RecombinationScheme recombScheme = fastjet::E_scheme;
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fastjet::JetDefinition *jetDef = NULL;
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// For hadronic collision, use hadronic Durham kT measure
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if(event[3].colType() != 0 || event[4].colType() != 0)
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jetDef = new fastjet::JetDefinition(fastjet::kt_algorithm, Rparam,
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recombScheme, strategy);
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// For e+e- collision, use e+e- Durham kT measure
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jetDef = new fastjet::JetDefinition(fastjet::ee_kt_algorithm,
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recombScheme, strategy);
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std::vector <fastjet::PseudoJet> fjInputs;
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// Reset Fastjet input
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// Loop over event record to decide what to pass to FastJet
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for (int i = 0; i < event.size(); ++i) {
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// (Final state && coloured+photons) only!
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if ( !event[i].isFinal()
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|| event[i].isLepton()
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|| event[i].id() == 23
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|| abs(event[i].id()) == 24
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|| abs(event[i].y()) > yPartonMax)
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// Store as input to Fastjet
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fjInputs.push_back( fastjet::PseudoJet (event[i].px(),
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event[i].py(), event[i].pz(),event[i].e() ) );
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// Do nothing for empty input
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if (int(fjInputs.size()) == 0) {
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// Run Fastjet algorithm
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fastjet::ClusterSequence clustSeq(fjInputs, *jetDef);
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// Extract kT of first clustering
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double pTFirst = sqrt(clustSeq.exclusive_dmerge_max(nJetMin-1));
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//==========================================================================
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// Class for user interaction with the merging
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class MyMergingHooks : public MergingHooks {
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// Default constructor
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// Functional definition of the merging scale
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virtual double tmsDefinition( const Event& event);
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// Function to dampen weights calculated from histories with lowest
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// multiplicity reclustered events that do not pass the ME cuts
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virtual double dampenIfFailCuts( const Event& inEvent );
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// Helper function for tms definition
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double myKTdurham(const Particle& RadAfterBranch,
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const Particle& EmtAfterBranch, int Type, double D );
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//--------------------------------------------------------------------------
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MyMergingHooks::MyMergingHooks() {}
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MyMergingHooks::~MyMergingHooks() {}
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//--------------------------------------------------------------------------
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double MyMergingHooks::dampenIfFailCuts( const Event& inEvent ){
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// Get pT for pure QCD 2->2 state
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for( int i=0; i < inEvent.size(); ++i)
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if(inEvent[i].isFinal() && inEvent[i].colType() != 0) {
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pT = sqrt(pow(inEvent[i].px(),2) + pow(inEvent[i].py(),2));
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// Veto history if lowest multiplicity event does not pass ME cuts
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if(pT < 10.) return 0.;
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//--------------------------------------------------------------------------
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// Definition of the merging scale
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double MyMergingHooks::tmsDefinition( const Event& event){
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// Cut only on QCD partons!
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// Count particle types
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int nFinalColoured = 0;
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for( int i=0; i < event.size(); ++i) {
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if(event[i].isFinal()){
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if(event[i].id() != 23 && abs(event[i].id()) != 24)
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if( event[i].colType() != 0)
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// Use MergingHooks in-built functions to get information on the hard process
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int nLeptons = nHardOutLeptons();
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int nQuarks = nHardOutPartons();
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int nResNow = nResInCurrent();
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// Check if photons, electrons etc. have been produced. If so, do not veto
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if(nFinalNow - ( (nLeptons+nQuarks)/2 - nResNow)*2 != nFinalColoured){
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// Sometimes, Pythia detaches the decay products even though no
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// resonance was put into the LHE file, to catch this, add another
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if(nFinalNow != nFinalColoured) return 0.;
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// Check that one parton has been produced. If not (e.g. in MPI), do not veto
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int nMPI = infoPtr->nMPI();
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if(nMPI > 1) return 0.;
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// Declare kT algorithm parameters
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// Declare final parton vector
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vector <int> FinalPartPos;
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FinalPartPos.clear();
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// Search event record for final state partons
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for (int i=0; i < event.size(); ++i)
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if(event[i].isFinal() && event[i].colType() != 0)
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FinalPartPos.push_back(i);
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// Find minimal Durham kT in event, using own function: Check
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// definition of separation
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int type = (event[3].colType() == 0 && event[4].colType() == 0) ? 1 : kTtype;
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double ktmin = event[0].e();
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for(int i=0; i < int(FinalPartPos.size()); ++i){
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// Compute separation to the beam axis for hadronic collisions
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if(type == -1 || type == -2) {
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double temp = event[FinalPartPos[i]].pT();
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kt12 = min(kt12, temp);
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// Compute separation to other final state jets
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for(int j=i+1; j < int(FinalPartPos.size()); ++j) {
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double temp = kTdurham( event[FinalPartPos[i]], event[FinalPartPos[j]],
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kt12 = min(kt12, temp);
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// Keep the minimal Durham separation
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ktmin = min(ktmin,kt12);
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// Return minimal Durham kT
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//--------------------------------------------------------------------------
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// Function to compute durham y separation from Particle input
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double MyMergingHooks::myKTdurham(const Particle& RadAfterBranch,
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const Particle& EmtAfterBranch, int Type, double D ){
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// Declare return variable
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// Save 4-momenta of final state particles
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Vec4 jet1 = RadAfterBranch.p();
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Vec4 jet2 = EmtAfterBranch.p();
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// Get angle between jets for e+e- collisions, make sure that
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// -1 <= cos(theta) <= 1
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if (jet1.pAbs()*jet2.pAbs() <=0.) costh = 1.;
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costh = costheta(jet1,jet2);
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// Calculate kt durham separation between jets for e+e- collisions
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ktdur = 2.0*min( pow(jet1.e(),2) , (pow(jet2.e(),2)) )*(1.0 - costh);
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} else if( Type == -1 ){
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// Get delta_eta and cosh(Delta_eta) for hadronic collisions
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double eta1 = 0.5*log( (jet1.e() + jet1.pz()) / (jet1.e() - jet1.pz()) );
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double eta2 = 0.5*log( (jet2.e() + jet2.pz()) / (jet2.e() - jet2.pz()) );
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// Get delta_phi and cos(Delta_phi) for hadronic collisions
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double pt1 = sqrt( pow(jet1.px(),2) + pow(jet1.py(),2) );
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double pt2 = sqrt( pow(jet2.px(),2) + pow(jet2.py(),2) );
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double cosdPhi = ( jet1.px()*jet2.px() + jet1.py()*jet2.py() ) / (pt1*pt2);
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double dPhi = acos( cosdPhi );
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// Calculate kT durham like fastjet
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ktdur = min( pow(pt1,2),pow(pt2,2) )
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* ( pow(eta1-eta2,2) + pow(dPhi,2) ) / pow(D,2);
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} else if( Type == -2 ){
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// Get delta_eta and cosh(Delta_eta) for hadronic collisions
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double eta1 = 0.5*log( (jet1.e() + jet1.pz()) / (jet1.e() - jet1.pz()) );
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double eta2 = 0.5*log( (jet2.e() + jet2.pz()) / (jet2.e() - jet2.pz()) );
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double coshdEta = cosh( eta1 - eta2 );
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// Get delta_phi and cos(Delta_phi) for hadronic collisions
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double pt1 = sqrt( pow(jet1.px(),2) + pow(jet1.py(),2) );
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double pt2 = sqrt( pow(jet2.px(),2) + pow(jet2.py(),2) );
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double cosdPhi = ( jet1.px()*jet2.px() + jet1.py()*jet2.py() ) / (pt1*pt2);
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// Calculate kT durham separation "SHERPA-like"
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ktdur = 2.0*min( pow(pt1,2),pow(pt2,2) )
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* ( coshdEta - cosdPhi ) / pow(D,2);
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//==========================================================================
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// Example main programm to illustrate merging
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int main( int argc, char* argv[] ){
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// Check that correct number of command-line arguments
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cerr << " Unexpected number of command-line arguments. \n You are"
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<< " expected to provide the arguments \n"
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<< " 1. Input file for settings \n"
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<< " 2. Full name of the input LHE file (with path) \n"
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<< " 3. Path for output histogram files \n"
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<< " Program stopped. " << endl;
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// 1. Input file for settings
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// 2. Path to input LHE file
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// 3. OUtput histogram path
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pythia.readFile(argv[1]);
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string iPath = string(argv[2]);
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string oPath = string(argv[3]);
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int nEvent = pythia.mode("Main:numberOfEvents");
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// Construct user inut for merging
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MergingHooks* myMergingHooks = new MyMergingHooks();
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pythia.setMergingHooksPtr( myMergingHooks );
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// For ISR regularisation off
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pythia.settings.forceParm("SpaceShower:pT0Ref",0.);
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// Declare histograms
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Hist histPTFirst("pT of first jet",100,0.,100.);
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Hist histPTSecond("pT of second jet",100,0.,100.);
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// Read in ME configurations
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pythia.init(iPath,false);
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if(pythia.flag("Main:showChangedSettings")) {
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pythia.settings.listChanged();
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// Start generation loop
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for( int iEvent=0; iEvent<nEvent; ++iEvent ){
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// Generate next event
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if( ! pythia.next()) continue;
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// Get CKKWL weight of current event
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double weight = pythia.info.mergingWeight();
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// Fill bins with CKKWL weight
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double pTfirst = pTfirstJet(pythia.event,1, 0.4);
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double pTsecnd = pTfirstJet(pythia.event,2, 0.4);
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histPTFirst.fill( pTfirst, weight);
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histPTSecond.fill( pTsecnd, weight);
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if(iEvent%1000 == 0) cout << iEvent << endl;
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} // end loop over events to generate
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// print cross section, errors
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// Normalise histograms
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* pythia.info.sigmaGen()
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* 1./ double(nEvent);
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histPTSecond *= norm;
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// Get the number of jets in the LHE file from the file name
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string jetsInLHEF = iPath.substr(iPath.size()-5, iPath.size());
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jetsInLHEF = jetsInLHEF.substr(0, jetsInLHEF.size()-4);
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// Write histograms to dat file. Use "jetsInLHEF" to label the files
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// Once all the samples up to the maximal desired jet multiplicity from the
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// matrix element are run, add all histograms to produce a
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// matrix-element-merged prediction
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suffix << jetsInLHEF << "_wv.dat";
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// Write histograms to file
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write.open( (char*)(oPath + "PTjet1_" + suffix.str()).c_str());
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histPTFirst.table(write);
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write.open( (char*)(oPath + "PTjet2_" + suffix.str()).c_str());
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histPTSecond.table(write);
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delete myMergingHooks;
added
removed
examples/main83.cc
