Rivet analyses

title: HRS_1988_I250824

$\eta$ spectrum in $e^+e^-$ collisions at 29 GeV

Experiment: HRS (PEP)

Inspire ID: 250824

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Lett. B205 (1988) 111-114

Beams: e+ e-

Beam energies: (14.5, 14.5)GeV

Run details: - Hadronic e+e- events at $\sqrt{s} = 29.$ GeV

$\eta$ meson momentum spectrum measured at $\sqrt{s} = 29.$ GeV using the HRS detector at PEP. The bin widths are not included in either the paper or HEPdata and have therefore been infered.

Source code:HRS_1988_I250824.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/Beam.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief Add a short analysis description here class HRS_1988_I250824 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(HRS_1988_I250824);


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

/// Book histograms and initialise projections before the run
void init() {
  declare(Beam(), "Beams");
  declare(FinalState(), "FS");
  declare(UnstableParticles(), "UFS");

  // Book histograms
  book(_h_eta, 1, 1, 1);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  if (_edges.empty()) _edges = _h_eta->xEdges();
  // 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");

  // 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);

  // Final state to get particle spectra
  for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles(Cuts::pid == 221)) {
    const double xE = p.E() / meanBeamMom;
    _h_eta->fill(map2string(xE));
  }
}

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


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

  const double fact = sqr(sqrtS()) / GeV2 * crossSection() / microbarn / sumOfWeights();
  scale(_h_eta, fact);
  for (auto& b : _h_eta->bins()) {
    const size_t idx = b.index();
    b.scaleW(1. / _axis.width(idx));
  }
}

/// @}


/// @name Histograms
/// @{
BinnedHistoPtr<string> _h_eta;
YODA::Axis<double> _axis{0.1435, 0.1765, 0.210, 0.244,  0.2785, 0.313,  0.347,
                         0.381,  0.4155, 0.45,  0.4925, 0.5525, 0.6215, 0.6905};
vector<string> _edges;
/// @}

};

RIVET_DECLARE_PLUGIN(HRS_1988_I250824);

} ```