Rivet analyses

title: OPAL_1998_I470419

Photon and Light Meson Production in Hadronic $Z^0$ Decays

Experiment: OPAL (LEP 1)

Inspire ID: 470419

Status: VALIDATED

Authors: - Peter Richardson

References: - Eur.Phys.J.C5:411-437,1998 - hep-ex/9805011

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 inclusive production rates and differential cross sections of photons and mesons with a final state containing photons have been measured with the OPAL detector at LEP. The light mesons covered by the measurements are the $\pi^0$, $\eta$, $\rho(770)^\pm$, $\omega(782)$, $\eta'(958)$ and $a_0(980)^\pm$.

Source code:OPAL_1998_I470419.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 photon/light meson paper /// /// @author Peter Richardson class OPAL_1998_I470419 : public Analysis { public:

RIVET_DEFAULT_ANALYSIS_CTOR(OPAL_1998_I470419);


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

void init() {
  declare(Beam(), "Beams");
  declare(ChargedFinalState(), "FS");
  declare(UnstableParticles(), "UFS");
  book(_histXePhoton, 2, 1, 1);
  book(_histXiPhoton, 3, 1, 1);
  book(_histXePi, 4, 1, 1);
  book(_histXiPi, 5, 1, 1);
  book(_histXeEta, 6, 1, 1);
  book(_histXiEta, 7, 1, 1);
  book(_histXeRho, 8, 1, 1);
  book(_histXiRho, 9, 1, 1);
  book(_histXeOmega, 10, 1, 1);
  book(_histXiOmega, 11, 1, 1);
  book(_histXeEtaPrime, 12, 1, 1);
  book(_histXiEtaPrime, 13, 1, 1);
  book(_histXeA0, 14, 1, 1);
  book(_histXiA0, 15, 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();
    double xi = -log(p.p3().mod() / meanBeamMom);
    double xE = p.E() / meanBeamMom;
    switch (id) {
      case 22: // Photons
        _histXePhoton->fill(xE);
        _histXiPhoton->fill(xi);
        break;
      case 111: // Neutral pions
        _histXePi->fill(xE);
        _histXiPi->fill(xi);
        break;
      case 221: // eta
        _histXeEta->fill(xE);
        _histXiEta->fill(xi);
        break;
      case 213: // Charged rho (770)
        _histXeRho->fill(xE);
        _histXiRho->fill(xi);
        break;
      case 223: // omega (782)
        _histXeOmega->fill(xE);
        _histXiOmega->fill(xi);
        break;
      case 331: // eta' (958)
        _histXeEtaPrime->fill(xE);
        _histXiEtaPrime->fill(xi);
        break;
      case 9000211: // Charged a_0 (980)
        _histXeA0->fill(xE);
        _histXiA0->fill(xi);
        break;
    }
  }
}


/// Finalize
void finalize() {
  scale(_histXePhoton, 1. / sumOfWeights());
  scale(_histXiPhoton, 1. / sumOfWeights());
  scale(_histXePi, 1. / sumOfWeights());
  scale(_histXiPi, 1. / sumOfWeights());
  scale(_histXeEta, 1. / sumOfWeights());
  scale(_histXiEta, 1. / sumOfWeights());
  scale(_histXeRho, 1. / sumOfWeights());
  scale(_histXiRho, 1. / sumOfWeights());
  scale(_histXeOmega, 1. / sumOfWeights());
  scale(_histXiOmega, 1. / sumOfWeights());
  scale(_histXeEtaPrime, 1. / sumOfWeights());
  scale(_histXiEtaPrime, 1. / sumOfWeights());
  scale(_histXeA0, 1. / sumOfWeights());
  scale(_histXiA0, 1. / sumOfWeights());
}

/// @}

private:

/// @{
Histo1DPtr _histXePhoton;
Histo1DPtr _histXiPhoton;
Histo1DPtr _histXePi;
Histo1DPtr _histXiPi;
Histo1DPtr _histXeEta;
Histo1DPtr _histXiEta;
Histo1DPtr _histXeRho;
Histo1DPtr _histXiRho;
Histo1DPtr _histXeOmega;
Histo1DPtr _histXiOmega;
Histo1DPtr _histXeEtaPrime;
Histo1DPtr _histXiEtaPrime;
Histo1DPtr _histXeA0;
Histo1DPtr _histXiA0;
/// @}

};

RIVET_DECLARE_ALIASED_PLUGIN(OPAL_1998_I470419, OPAL_1998_S3749908);

} ```

Aliases: - OPAL_1998_S3749908