Rivet analyses

title: HRS_1992_I339573

Spectrum for $\Lambda$ production at 29 GeV

Experiment: HRS (PEP)

Inspire ID: 339573

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev. D45 (1992) 3949-3954, 1992

Beams: e+ e-

Beam energies: (14.5, 14.5)GeV

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

Spectrum for the production of $\Lambda$ baryons at 29 GeV measured by the HRS experiment.

Source code:HRS_1992_I339573.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_1992_I339573 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(HRS_1992_I339573);


/// @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_lambda, 1, 1, 1);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  if (_edges.empty()) _edges = _h_lambda->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::abspid == 3122)) {
    double xE = p.E() / meanBeamMom;
    _h_lambda->fill(map2string(xE));
  }
}

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


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

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

/// @}


/// @name Histograms
/// @{
BinnedHistoPtr<string> _h_lambda;
YODA::Axis<double> _axis{0.0, 0.15, 0.2, 0.25, 0.3, 0.4, 0.55, 0.75};
vector<string> _edges;
/// @}

};

RIVET_DECLARE_PLUGIN(HRS_1992_I339573);

} ```