Rivet analyses

title: OPAL_1996_I402487

$J/\psi$ and $\psi^\prime$ Production in Hadronic $Z^0$ Decays

Experiment: OPAL (LEP 1)

Inspire ID: 402487

Status: VALIDATED

Authors: - Peter Richardson

References: - Z.Phys. C70 (1996) 197-210

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 $J/\psi$ and $\psi^\prime$ mesons measured by the OPAL experiment at LEP. The fragmentation function for $J/\psi$ and the multiplicities of $J/\psi$ and $\psi^\prime$ are included.

Source code:OPAL_1996_I402487.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 OPAL J/Psi fragmentation function paper /// /// @author Peter Richardson class OPAL_1996_I402487 : public Analysis { public:

RIVET_DEFAULT_ANALYSIS_CTOR(OPAL_1996_I402487);


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

void init() {
  declare(Beam(), "Beams");
  declare(ChargedFinalState(), "FS");
  declare(UnstableParticles(), "UFS");
  book(_histXpJPsi, 1, 1, 1);
  book(_multJPsi, 2, 1, 1);
  book(_multPsiPrime, 2, 1, 2);
  book(_weightSum, "_weightSum");
}


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()) {
    if (p.abspid() == 443) {
      double xp = p.p3().mod() / meanBeamMom;
      _histXpJPsi->fill(xp);
      _multJPsi->fill(91.2);
      _weightSum->fill();
    }
    else if (p.abspid() == 100443) {
      _multPsiPrime->fill(91.2);
    }
  }
}


/// Finalize
void finalize() {
  if (_weightSum->val() > 0.) scale(_histXpJPsi, 0.1 / *_weightSum);
  scale(_multJPsi, 1. / sumOfWeights());
  scale(_multPsiPrime, 1. / sumOfWeights());
}

/// @}


/// @{
CounterPtr _weightSum;
Histo1DPtr _histXpJPsi;
Histo1DPtr _multJPsi;
Histo1DPtr _multPsiPrime;
/// @}

};

RIVET_DECLARE_ALIASED_PLUGIN(OPAL_1996_I402487, OPAL_1996_S3257789);

} ```

Aliases: - OPAL_1996_S3257789