Rivet analyses

e+e− mass distribution in J/ψ → η′e+e−

Experiment: BESIII (BEPC)

Inspire ID: 1692688

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 99 (2019) 1, 012013

Beams: * *

Beam energies: ANY

Run details: - Any process producing J/psi

e+e− mass distribution in J/ψ → η′e+e−. Data read from plots in paper which are not efficiency corrected.

Source code:BESIII_2019_I1692688.cc

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

namespace Rivet {


  /// @brief J/psi -> eta' e+e-
  class BESIII_2019_I1692688 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2019_I1692688);


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

    /// Book histograms and initialise projections before the run
    void init() {
      UnstableParticles ufs = UnstableParticles(Cuts::abspid == PID::JPSI);
      declare(ufs, "UFS");
      DecayedParticles psi(ufs);
      psi.addStable(PID::PI0);
      psi.addStable(PID::ETAPRIME);
      declare(psi, "PSI");
      for (unsigned int ix = 0; ix < 2; ++ix) book(_h[ix], 1, 1, ix + 1);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // define the decay mode
      static const map<PdgId, unsigned int>& mode = {{PID::ETAPRIME, 1}, {11, 1}, {-11, 1}};
      DecayedParticles psi = apply<DecayedParticles>(event, "PSI");
      // loop over particles
      for (unsigned int ix = 0; ix < psi.decaying().size(); ++ix) {
        if (!psi.modeMatches(ix, 3, mode)) continue;
        const Particle& em = psi.decayProducts()[ix].at(11)[0];
        const Particle& ep = psi.decayProducts()[ix].at(-11)[0];
        double mee = (ep.momentum() + em.momentum()).mass();
        for (unsigned int ix = 0; ix < 2; ++ix) _h[ix]->fill(mee);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      for (unsigned int ix = 0; ix < 2; ++ix) normalize(_h[ix], 1., false);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h[2];
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESIII_2019_I1692688);

}