Rivet analyses

title: OPAL_1995_I393503

$K^0$ Production in Hadronic $Z^0$ Decays

Experiment: OPAL (LEP)

Inspire ID: 393503

Status: VALIDATED

Authors: - Peter Richardson

References: - Z.Phys. C67 (1995) 389-402, 1995

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)

The production of $K^0$ mesons measured using 1.3 million $Z^0$ events by the OPAL experiment at LEP. Only the fragmentation function is implemented.

Source code:OPAL_1995_I393503.cc

```c++ // -- 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 kaon spectra at LEP1 class OPAL_1995_I393503 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(OPAL_1995_I393503);


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

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

  // Book histograms
  book(_h_K0_x, 2, 1, 1);
  book(_h_K0_xi, 3, 1, 1);
}


/// Perform the per-event analysis
void analyze(const Event& event) {

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

  for (const Particle& p : ufs.particles(Cuts::pid == 130 or Cuts::pid == 310)) {
    double xp = p.p3().mod() / meanBeamMom;
    _h_K0_x->fill(xp);
    _h_K0_xi->fill(-log(xp));
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  scale(_h_K0_x, 1. / sumOfWeights());
  scale(_h_K0_xi, 1. / sumOfWeights());
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_K0_x, _h_K0_xi;
/// @}

};

RIVET_DECLARE_PLUGIN(OPAL_1995_I393503);

} ```