Rivet analyses

title: PLUTO_1985_I215869

Energy-Energy correlation at 34.6 GeV

Experiment: PLUTO (Petra)

Inspire ID: 215869

Status: VALIDATED

Authors: - Peter Richardson

References: - Z.Phys. C28 (1985) 365, 1985

Beams: e+ e-

Beam energies: (17.3, 17.3)GeV

Run details: - e+e- to hadrons at 34.6 GeV CMS

Measurement of the energy-energy correlation at 34.6 GeV

Source code:PLUTO_1985_I215869.cc

```c++ // -- C++ --

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

namespace Rivet {

/// @brief EEC at 34.6 GeV class PLUTO_1985_I215869 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(PLUTO_1985_I215869);


/// @name Analysis methods
/// @{

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

  // Initialise and register projections
  declare(FinalState(), "FS");
  // Book histograms
  book(_h_EEC, 1, 1, 1);
  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 cosij = mom3_i.unit().dot(mom3_j.unit());
      //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.;
      _h_EEC->fill(cosij, eec);
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  scale(_h_EEC, 1. / *_weightSum);
}
/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_EEC;
CounterPtr _weightSum;
/// @}

};

RIVET_DECLARE_PLUGIN(PLUTO_1985_I215869);

} ```