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OPAL_2004_I648738

Quark and gluon jet fragmentation functions
Experiment: OPAL (LEP)
Inspire ID: 648738
Status: VALIDATED
Authors:
  • Daniel Reichelt
References:
  • Eur.Phys.J. C37 (2004) no.1, 25-47
  • hep-ex/0404026
Beams: e+ e-
Beam energies: (6.4, 6.4); (13.4, 13.4); (24.0, 24.0); (45.6, 45.6); (46.5, 46.5); (48.5, 48.5); (98.5, 98.5) GeV
Run details:
  • For quark fragmentation $e^+e^-\to q\bar{q}$ events are required, while for gluon fragmentation the fictional $e^+e^-\to gg$ process is required.

Measurement of the fragmentation functions for quarks and gluons at LEP. Useful for studying the properties of gluon jets and the differences between quark and gluon jets. For the study of gluon jets the fictional $e^+e^-\to g g $ process must be used. The data in histograms labelled "hemisphere fragmentation" are measured from jets defined by hemispheres, with an energy scale defined by $E=\sqrt{s}/2$, while data in histograms named "durham fragmentation" are measured from jets defined by the durham algorithm with $Q_\mathrm{jet}=E_\mathrm{jet}\sin(\theta/2)$ as the energy scale. The rivet analysis defines the jet flavour from the initial quarks, as the data are corrected for impurities, and defines all jets as hemispheres with energy scale $E=\sqrt{s}/2$.

Source code: OPAL_2004_I648738.cc
  1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/FinalState.hh"
  4#include "Rivet/Projections/ChargedFinalState.hh"
  5
  6namespace Rivet {
  7
  8
  9  class OPAL_2004_I648738 : public Analysis {
 10  public:
 11
 12    /// Constructor
 13    OPAL_2004_I648738()
 14      : Analysis("OPAL_2004_I648738"), _sumW(3), _histo_xE(3)
 15    {    }
 16
 17
 18    /// @name Analysis methods
 19    //@{
 20    void init() {
 21      declare(FinalState(), "FS");
 22      declare(ChargedFinalState(), "CFS");
 23      unsigned int ih=0;
 24      if (inRange(0.5*sqrtS()/GeV, 4.0, 9.0)) {
 25	ih = 1;
 26      }
 27      else if (inRange(0.5*sqrtS()/GeV, 9.0, 19.0)) {
 28	ih = 2;
 29      }
 30      else if (inRange(0.5*sqrtS()/GeV, 19.0, 30.0)) {
 31	ih = 3;
 32      }
 33      else if (inRange(0.5*sqrtS()/GeV, 45.5, 45.7)) {
 34	ih = 5;
 35      }
 36      else if (inRange(0.5*sqrtS()/GeV, 30.0, 70.0)) {
 37	ih = 4;
 38      }
 39      else if (inRange(0.5*sqrtS()/GeV, 91.5, 104.5)) {
 40	ih = 6;
 41      }
 42      assert(ih>0);
 43      // book the histograms
 44      book(_histo_xE[0], ih+5,1,1);
 45      book(_histo_xE[1], ih+5,1,2);
 46      if(ih<5) book(_histo_xE[2] ,ih+5,1,3);
 47      book(_sumW[0], "_sumW_0");
 48      book(_sumW[1], "_sumW_1");
 49      book(_sumW[2], "_sumW_2");
 50    }
 51
 52    /// Perform the per-event analysis
 53    void analyze(const Event& event) {
 54      // find the initial quarks/gluons
 55      Particles initial;
 56      for (ConstGenParticlePtr p : HepMCUtils::particles(event.genEvent())) {
 57        ConstGenVertexPtr pv = p->production_vertex();
 58        const PdgId pid = abs(p->pdg_id());
 59        if(!( (pid>=1&&pid<=5) || pid ==21) ) continue;
 60        bool passed = false;
 61        for (ConstGenParticlePtr pp : HepMCUtils::particles(pv, Relatives::PARENTS)) {
 62          const PdgId ppid = abs(pp->pdg_id());
 63          passed = (ppid == PID::ELECTRON || ppid == PID::HIGGS ||
 64                    ppid == PID::ZBOSON   || ppid == PID::GAMMA);
 65          if(passed) break;
 66        }
 67        if(passed) initial.push_back(Particle(*p));
 68        }
 69        if(initial.size()!=2) {
 70          vetoEvent;
 71        }
 72        // type of event
 73        unsigned int itype=2;
 74        if(initial[0].pid()==-initial[1].pid()) {
 75          PdgId pid = abs(initial[0].pid());
 76          if(pid>=1&&pid<=4)
 77            itype=0;
 78          else
 79            itype=1;
 80        }
 81        assert(itype<_histo_xE.size());
 82
 83      // fill histograms
 84      _sumW[itype]->fill(2.);
 85      const Particles& chps = applyProjection<FinalState>(event, "CFS").particles();
 86      for(const Particle& p : chps) {
 87        double xE = 2.*p.E()/sqrtS();
 88	_histo_xE[itype]->fill(xE);
 89      }
 90
 91    }
 92
 93
 94    /// Normalise histograms etc., after the run
 95    void finalize() {
 96      for(unsigned int ix=0;ix<_histo_xE.size();++ix) {
 97	if(_sumW[ix]->val()>0.) scale(_histo_xE[ix],1./ *_sumW[ix]);
 98      }
 99    }
100    //@}
101
102
103  private:
104
105    vector<CounterPtr> _sumW;
106
107    /// @name Histograms
108    //@{
109    vector<Histo1DPtr> _histo_xE;
110    //@}
111
112
113  };
114
115  // The hook for the plugin system
116  RIVET_DECLARE_PLUGIN(OPAL_2004_I648738);
117
118}