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DELPHI_1997_I428178

Flavour separated charged particle spectra at LEP1
Experiment: DELPHI (LEP)
Inspire ID: 428178
Status: VALIDATED
Authors:
  • Peter Richardson
References:
  • Phys.Lett. B398 (1997) 194-206, 1997
Beams: e+ e-
Beam energies: (45.6, 45.6) GeV
Run details:
  • Hadronic Z decay events generated on the Z pole ($\sqrt{s} = 91.2$ GeV)

Charged particle momentum scaled momentum spectrum, separated into flavours of the initial quarks, at LEP1

Source code: DELPHI_1997_I428178.cc
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/Beam.hh"
#include "Rivet/Projections/ChargedFinalState.hh"

#define I_KNOW_THE_INITIAL_QUARKS_PROJECTION_IS_DODGY_BUT_NEED_TO_USE_IT
#include "Rivet/Projections/InitialQuarks.hh"

namespace Rivet {


  /// @brief charged particle spectra
  class DELPHI_1997_I428178 : public Analysis {
  public:

    /// Constructor
    DEFAULT_RIVET_ANALYSIS_CTOR(DELPHI_1997_I428178);


    /// @name Analysis methods
    //@{

    /// Book histograms and initialise projections before the run
    void init() {
      declare(Beam(), "Beams");
      declare(ChargedFinalState(), "FS");
      declare(InitialQuarks(), "IQF");


      // Book histograms
      book(_h_bottom, 1, 1, 1);
      book(_h_charm , 1, 1, 2);
      book(_h_light , 1, 1, 3);

      book(_wBottom,"TMP/wBottom");
      book(_wCharm ,"TMP/wCharm" );
      book(_wLight ,"TMP/wLight" );
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // First, veto on leptonic events by requiring at least 4 charged FS particles
      const FinalState& fs = apply<FinalState>(event, "FS");
      const size_t numParticles = fs.particles().size();

      // Even if we only generate hadronic events, we still need a cut on numCharged >= 2.
      if (numParticles < 2) {
        MSG_DEBUG("Failed leptonic event cut");
        vetoEvent;
      }
      MSG_DEBUG("Passed leptonic event cut");

      int flavour = 0;
      const InitialQuarks& iqf = apply<InitialQuarks>(event, "IQF");

      // If we only have two quarks (qqbar), just take the flavour.
      // If we have more than two quarks, look for the highest energetic q-qbar pair.
      if (iqf.particles().size() == 2) {
        flavour = iqf.particles().front().abspid();
      }
      else {
        map<int, double> quarkmap;
        for (const Particle& p : iqf.particles()) {
          if (quarkmap[p.pid()] < p.E()) {
            quarkmap[p.pid()] = p.E();
          }
        }
        double maxenergy = 0.;
        for (int i = 1; i <= 5; ++i) {
          if (quarkmap[i]+quarkmap[-i] > maxenergy) {
            flavour = i;
          }
        }
      }
      if     (flavour==5) _wBottom->fill();
      else if(flavour==4) _wCharm ->fill();
      else                _wLight ->fill();
      // Get beams and average beam momentum
      const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
      const double meanBeamMom = ( beams.first.p3().mod() +
                                   beams.second.p3().mod() ) / 2.0;
      MSG_DEBUG("Avg beam momentum = " << meanBeamMom);
      for (const Particle& p : fs.particles()) {
        double xp = p.p3().mod()/meanBeamMom;
	if     (flavour==5) _h_bottom->fill(xp);
	else if(flavour==4) _h_charm ->fill(xp);
	else                _h_light ->fill(xp);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {

      scale(_h_bottom, 1./ *_wBottom);
      scale(_h_charm , 1./ *_wCharm);
      scale(_h_light , 1./ *_wLight);

    }

    //@}


    /// @name Histograms
    //@{
    Histo1DPtr _h_bottom, _h_charm, _h_light;
    CounterPtr _wBottom, _wCharm, _wLight;
    //@}


  };


  // The hook for the plugin system
  DECLARE_RIVET_PLUGIN(DELPHI_1997_I428178);


}