Rivet analyses

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++ -*-
#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);

}