Rivet analyses

title: 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

```c++ // -- 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
RIVET_DEFAULT_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) {
  if (_edges.empty()) _edges = _histEEC->xEdges();
  // 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(map2string(thetaij), eec);
        _histAEEC->fill(map2string(thetaij), -eec);
      }
      else {
        _histEEC_Pi->fill(map2string(180. - thetaij), eec);
        _histAEEC->fill(map2string(180. - thetaij), eec);
      }
    }
  }
}

string map2string(const double value) const {
  const size_t idx = _axis.index(value) - 1;
  if (idx < _edges.size()) return _edges[idx];
  return "OTHER";
}

/// Normalise histograms etc., after the run
void finalize() {
  // convert degree -> millirad (due units) and divide bin width in degrees (as bin width not in hist)
  scale(_histEEC, 180.0 / M_PI * 1000. / 3.6 / *_weightSum);
  scale(_histEEC_Pi, 180.0 / M_PI * 1000. / 3.6 / *_weightSum);
  scale(_histAEEC, 180.0 / M_PI * 1000. / 3.6 / *_weightSum);
}

/// @}

/// @name Histograms
/// @{
CounterPtr _weightSum;
BinnedHistoPtr<string> _histEEC, _histEEC_Pi, _histAEEC;
YODA::Axis<double> _axis{0.0,  3.6,  7.2,  10.8, 14.4, 18.0, 21.6, 25.2, 28.8, 32.4, 36.0, 39.6, 43.2,
                         46.8, 50.4, 54.0, 57.6, 61.2, 64.8, 68.4, 72.0, 75.6, 79.2, 82.8, 86.4, 90.0};
vector<string> _edges;

/// @}

};

RIVET_DECLARE_PLUGIN(MAC_1985_I202924);

} ```