Rivet analyses

η^′ → e⁺e⁻γ decays

Experiment: BESIII (BEPC)

Inspire ID: 1364494

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev. D92 (2015) 012001, 2015

Beams: * *

Beam energies: ANY

Run details: - Events with eta prime decays, either particle guns or collisions.

Differential decay rates for η^′ → e⁺e⁻γ decays

Source code:`BESIII_2015_I1364494.cc`

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/DecayedParticles.hh"
#include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {


  /// @brief eta' -> gamma e+e-
  class BESIII_2015_I1364494 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2015_I1364494);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      UnstableParticles ufs = UnstableParticles(Cuts::pid == 331);
      declare(ufs, "UFS");
      DecayedParticles ETA(ufs);
      ETA.addStable(PID::PI0);
      declare(ETA, "ETA");
      // Book histograms
      book(_h_m, 1, 1, 3);
      book(_netap, "TMP/netap");
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId, unsigned int>& mode0 = {{22, 2}};
      static const map<PdgId, unsigned int>& mode1 = {{11, 1}, {-11, 1}, {22, 1}};
      // Loop over eta' mesons
      DecayedParticles ETA = apply<DecayedParticles>(event, "ETA");
      // loop over particles
      for (unsigned int ix = 0; ix < ETA.decaying().size(); ++ix) {
        // reference mode for denominator
        if (ETA.modeMatches(ix, 2, mode0)) _netap->fill();
        // select right decay mode
        else if (ETA.modeMatches(ix, 3, mode1)) {
          const Particle& ep = ETA.decayProducts()[ix].at(11)[0];
          const Particle& em = ETA.decayProducts()[ix].at(-11)[0];
          _h_m->fill((em.momentum() + ep.momentum()).mass());
        }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {

      // divide by no so BR and mult by bin width
      // and 100 as in %
      scale(_h_m, 0.1 * 100. / *_netap);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_m;
    CounterPtr _netap;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESIII_2015_I1364494);


}

Rivet analyses

η′ → e+e−γ decays

Source code:BESIII_2015_I1364494.cc

η^′ → e⁺e⁻γ decays

Source code:`BESIII_2015_I1364494.cc`