Rivet analyses

Strange baryon production in Z hadronic decays at OPAL

Experiment: OPAL (LEP 1)

Inspire ID: 421978

Status: VALIDATED

Authors: - Peter Richardson

References: - Z. Phys. C, 73, 569–586 (1997)

Beams: e+ e-

Beam energies: (45.6, 45.6)GeV

Run details: - Hadronic Z decay events generated on the Z pole ($\sqrt{s} = 91.2$ GeV)

Measurement of the Ξ−, Λ0, Σ+(1385), Σ−(1385), Ξ0(1530) and Λ0(1520) scaled momentum distributions by OPAL at LEP 1. The paper also has the production cross-sections of these particles, but that is not implemented in Rivet.

Source code:OPAL_1997_I421978.cc

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/Beam.hh"
#include "Rivet/Projections/ChargedFinalState.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {


  /// @brief OPAL strange baryon paper
  ///
  /// @author Peter Richardson
  class OPAL_1997_I421978 : public Analysis {
  public:

    RIVET_DEFAULT_ANALYSIS_CTOR(OPAL_1997_I421978);


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

    void init() {
      declare(Beam(), "Beams");
      declare(ChargedFinalState(), "FS");
      declare(UnstableParticles(), "UFS");

      book(_histXpLambda, 1, 1, 1);
      book(_histXiLambda, 2, 1, 1);
      book(_histXpXiMinus, 3, 1, 1);
      book(_histXiXiMinus, 4, 1, 1);
      book(_histXpSigma1385Plus, 5, 1, 1);
      book(_histXiSigma1385Plus, 6, 1, 1);
      book(_histXpSigma1385Minus, 7, 1, 1);
      book(_histXiSigma1385Minus, 8, 1, 1);
      book(_histXpXi1530, 9, 1, 1);
      book(_histXiXi1530, 10, 1, 1);
      book(_histXpLambda1520, 11, 1, 1);
      book(_histXiLambda1520, 12, 1, 1);
    }


    void analyze(const Event& e) {
      // First, veto on leptonic events by requiring at least 4 charged FS particles
      const FinalState& fs = apply<FinalState>(e, "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>(e, "Beams").beams();
      const double meanBeamMom = (beams.first.p3().mod() + beams.second.p3().mod()) / 2.0;
      MSG_DEBUG("Avg beam momentum = " << meanBeamMom);

      // Final state of unstable particles to get particle spectra
      const UnstableParticles& ufs = apply<UnstableParticles>(e, "UFS");

      for (const Particle& p : ufs.particles()) {
        const int id = p.abspid();
        if (!inRange(id, 3000, 3999) && id != 102134) continue;

        const double xE = p.E() / meanBeamMom;
        const double xp = p.p3().mod() / (2 * meanBeamMom);
        const double xi = -log(xp);

        switch (id) {
          case 3312:
            _histXpXiMinus->fill(xE);
            _histXiXiMinus->fill(xi);
            break;
          case 3224:
            _histXpSigma1385Plus->fill(xE);
            _histXiSigma1385Plus->fill(xi);
            break;
          case 3114:
            _histXpSigma1385Minus->fill(xE);
            _histXiSigma1385Minus->fill(xi);
            break;
          case 3122:
            _histXpLambda->fill(xE);
            _histXiLambda->fill(xi);
            break;
          case 3324:
            _histXpXi1530->fill(xE);
            _histXiXi1530->fill(xi);
            break;
          case 102134:
            _histXpLambda1520->fill(xE);
            _histXiLambda1520->fill(xi);
            break;
        }
      }
    }


    /// Finalize
    void finalize() {
      double fact = 1. / sumOfWeights();
      scale(_histXpLambda, fact);
      scale(_histXiLambda, fact);
      scale(_histXpXiMinus, fact);
      scale(_histXiXiMinus, fact);
      scale(_histXpSigma1385Plus, fact);
      scale(_histXiSigma1385Plus, fact);
      scale(_histXpSigma1385Minus, fact);
      scale(_histXiSigma1385Minus, fact);
      scale(_histXpXi1530, fact);
      scale(_histXiXi1530, fact);
      scale(_histXpLambda1520, fact);
      scale(_histXiLambda1520, fact);
    }

    /// @}


  private:

    /// @name Histograms
    /// @{
    Histo1DPtr _histXpLambda;
    Histo1DPtr _histXiLambda;
    Histo1DPtr _histXpXiMinus;
    Histo1DPtr _histXiXiMinus;
    Histo1DPtr _histXpSigma1385Plus;
    Histo1DPtr _histXiSigma1385Plus;
    Histo1DPtr _histXpSigma1385Minus;
    Histo1DPtr _histXiSigma1385Minus;
    Histo1DPtr _histXpXi1530;
    Histo1DPtr _histXiXi1530;
    Histo1DPtr _histXpLambda1520;
    Histo1DPtr _histXiLambda1520;
    /// @}
  };


  RIVET_DECLARE_ALIASED_PLUGIN(OPAL_1997_I421978, OPAL_1997_S3396100);

}

Aliases: - OPAL_1997_S3396100