Rivet analyses

title: CELLO_1982_I12010

Energy-Energy correlation at 22 and 34 GeV

Experiment: CELLO (Petra)

Inspire ID: 12010

Status: VALIDATED

Authors: - Peter Richardson

References: - Z.Phys. C14 (1982) 95, 1982

Beams: e+ e-

Beam energies: (11.0, 11.0); (17.0, 17.0)GeV

Run details: - e+e- to hadrons at 22 and 34 GeV CMS.

Measurement of the energy-energy correlation, and its assymetry, at centre-of-mass energies 22 and 34 GeV.

Source code:CELLO_1982_I12010.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/Beam.hh"

include "Rivet/Projections/FinalState.hh"

namespace Rivet {

/// @brief Add a short analysis description here class CELLO_1982_I12010 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(CELLO_1982_I12010);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  declare(FinalState(), "FS");

  // Book histograms
  size_t ih = 1;
  for (double eVal : allowedEnergies()) {
    const string en = toString(round(eVal));
    if (isCompatibleWithSqrtS(eVal)) _sqs = en;
    book(_h[en + "EEC"], 1, 1, ih);
    book(_h[en + "AEEC"], 3, 1, ih);
    book(_c[en], "TMP/weightSum" + en);
    ++ih;
  }
  raiseBeamErrorIf(_sqs.empty());
}


/// Perform the per-event analysis
void analyze(const Event& event) {

  if (edges[0].empty()) edges[0] = _h[_sqs + "EEC"]->xEdges();
  if (edges[1].empty()) edges[1] = _h[_sqs + "AEEC"]->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) vetoEvent;
  _c[_sqs]->fill();

  const double Evis2 = sqr(sum(fs.particles(), Kin::E, 0.0));
  // (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->p3();
      const Vector3 mom3_j = p_j->p3();
      const double energy_i = p_i->E();
      const double energy_j = p_j->E();
      const double thetaij = mom3_i.unit().angle(mom3_j.unit());
      double eec = (energy_i * energy_j) / Evis2;
      if (p_i != p_j) eec *= 2.;
      _h[_sqs + "EEC"]->fill(map2string(thetaij, 0), eec);
      if (thetaij < 0.5 * M_PI) {
        _h[_sqs + "AEEC"]->fill(map2string(thetaij, 1), -eec);
      }
      else {
        _h[_sqs + "AEEC"]->fill(map2string(M_PI - thetaij, 1), eec);
      }
    }
  }
}

string map2string(const double val, const size_t axis) const {
  const size_t idx = axes[axis].index(val);
  if (idx && idx <= edges[axis].size()) return edges[axis][idx - 1];
  return "OTHER";
}

/// Normalise histograms etc., after the run
void finalize() {
  for (const auto& item : _c) {
    size_t ih = 0;
    for (const string& obs : vector<string>{"EEC"s, "AEEC"s}) {
      scale(_h[item.first + obs], 1.0 / item.second->sumW());
      for (auto& b : _h[item.first + obs]->bins()) {
        b.scaleW(1.0 / axes[ih].width(b.index()));
      }
      ++ih;
    }
  }
}

/// @}


/// @name Histograms
/// @{
map<string, BinnedHistoPtr<string>> _h;
map<string, CounterPtr> _c;
vector<string> edges[2];
string _sqs = "";
YODA::Axis<double> axes[2] = {YODA::Axis<double>(50, 0.0, M_PI),
                              YODA::Axis<double>(24, 0.0628, 0.5 * M_PI)};
/// @}

};

RIVET_DECLARE_PLUGIN(CELLO_1982_I12010); } ```