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Rivet analyses reference

MAC_1985_I202924

Energy-Energy correlation at $E_{\text{CMS}}=29$ GeV
Experiment: MAC (PEP)
Inspire ID: 202924
Status: VALIDATED
Authors:
  • Peter Richardson
References:
  • Phys.Rev. D31 (1985) 2724, 1985
Beams: e- e+
Beam energies: (14.5, 14.5) GeV
Run details:
  • e+ e- to hadrons

Measurement of the energy-energy correlation, and its assymetry in $e^+e^-$ collisions by MAC at 29 GeV.

Source code: MAC_1985_I202924.cc
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"

namespace Rivet {


  /// @brief EEC at 29 GeV
  class MAC_1985_I202924 : public Analysis {
  public:

    /// Constructor
    DEFAULT_RIVET_ANALYSIS_CTOR(MAC_1985_I202924);


    /// @name Analysis methods
    //@{

    /// Book histograms and initialise projections before the run
    void init() {

      // Initialise and register projections
      declare(FinalState(), "FS");

      book(_histEEC   , 1, 1, 1);
      book(_histEEC_Pi, 1, 1, 2);
      book(_histAEEC  , 1, 1, 3);
      book(_weightSum,"TMP/weightSum");

    }


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

      double Evis = 0.0;
      for( const Particle& p : fs.particles()) {
        Evis += p.E();
      }
      double Evis2 = sqr(Evis);
      // (A)EEC
      // Need iterators since second loop starts at current outer loop iterator, i.e. no "foreach" here!
      for (Particles::const_iterator p_i = fs.particles().begin(); p_i != fs.particles().end(); ++p_i) {
        for (Particles::const_iterator p_j = p_i; p_j != fs.particles().end(); ++p_j) {
          const Vector3 mom3_i = p_i->momentum().p3();
          const Vector3 mom3_j = p_j->momentum().p3();
          const double energy_i = p_i->momentum().E();
          const double energy_j = p_j->momentum().E();
          const double thetaij = mom3_i.unit().angle(mom3_j.unit())/M_PI*180.;
          double eec = (energy_i*energy_j) / Evis2;
	  if(p_i != p_j) eec *= 2.;
          if (thetaij < 90.) {
	    _histEEC ->fill(thetaij,  eec);
            _histAEEC->fill(thetaij, -eec);
	  }
          else {
	    _histEEC_Pi->fill(180.-thetaij, eec);
            _histAEEC  ->fill(180.-thetaij, eec);
	  }
        }
      }
    }

    /// Normalise histograms etc., after the run
    void finalize() {
      scale(_histEEC   , 180.0/M_PI*1000./ *_weightSum);
      scale(_histEEC_Pi, 180.0/M_PI*1000./ *_weightSum);
      scale(_histAEEC  , 180.0/M_PI*1000./ *_weightSum);
    }

    //@}

    /// @name Histograms
    //@{
    Histo1DPtr _histEEC, _histEEC_Pi, _histAEEC;
    CounterPtr _weightSum;
    //@}

  };


  // The hook for the plugin system
  DECLARE_RIVET_PLUGIN(MAC_1985_I202924);


}