Rivet analyses

title: HRS_1986_I17781

Spectra for $\Lambda^0$ production at 29 GeV

Experiment: HRS (PEP)

Inspire ID: 17781

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 56 (1986) 1346

Beams: e+ e-

Beam energies: (14.5, 14.5)GeV

Run details: - e+ e- to hadrons

Measurement of the $\Lambda^0$ and spectra at 29 GeV by the HRS experiment. In addition to the spectra the rapidity of the $\Lambda^0$ is measured with respect to the thrust axis.

Source code:HRS_1986_I17781.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/Beam.hh"

include "Rivet/Projections/ChargedFinalState.hh"

include "Rivet/Projections/Thrust.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief Lambda production at 29 GeV class HRS_1986_I17781 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(HRS_1986_I17781);


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

/// Book histograms and initialise projections before the run
void init() {
  declare(UnstableParticles(), "UFS");
  const ChargedFinalState cfs;
  declare(cfs, "CFS");
  declare(Thrust(cfs), "Thrust");
  book(_h_spect, 1, 1, 1);
  book(_h_rap, 2, 1, 1);
  book(_h_mult, 3, 1, 1);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  const ChargedFinalState& cfs = apply<ChargedFinalState>(event, "CFS");
  const size_t numParticles = cfs.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");
  // Thrust
  const Thrust& thrust = apply<Thrust>(event, "Thrust");
  UnstableParticles ufs = apply<UnstableParticles>(event, "UFS");
  for (const Particle& p : ufs.particles(Cuts::abspid == 3122)) {
    double xE = 2. * p.E() / sqrtS();
    Vector3 mom3 = p.p3();
    const double energy = p.E();
    double modp = mom3.mod();
    double beta = modp / energy;
    const double momT = dot(thrust.thrustAxis(), mom3);
    const double rapidityT = 0.5 * std::log((energy + momT) / (energy - momT));
    _h_spect->fill(xE, 1. / beta);
    _h_rap->fill(abs(rapidityT));
    _h_mult->fill(29);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  scale(_h_spect, sqr(sqrtS()) * crossSection() / nanobarn / sumOfWeights());
  scale(_h_rap, 1. / sumOfWeights());
  scale(_h_mult, 1. / sumOfWeights());
}

///@}


/// @name Histograms
///@{
Histo1DPtr _h_spect, _h_rap;
BinnedHistoPtr<int> _h_mult;
///@}

};

RIVET_DECLARE_PLUGIN(HRS_1986_I17781);

} ```