Rivet analyses

Mass distributions in J/ψ → γη′π+π−

Experiment: BESIII (BEPC)

Inspire ID: 1437949

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 117 (2016) 4, 042002

Beams: * *

Beam energies: ANY

Run details: - Any process producing J/psi, originally e+e-

Mass distributions in J/ψ → γη′π+π−

Source code:BESIII_2016_I1437949.cc

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

namespace Rivet {


  /// @brief J/psi -> gamma eta' pi+pi-
  class BESIII_2016_I1437949 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2016_I1437949);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      UnstableParticles ufs = UnstableParticles(Cuts::abspid == 443);
      declare(ufs, "UFS");
      DecayedParticles PSI(ufs);
      PSI.addStable(PID::ETA);
      PSI.addStable(PID::ETAPRIME);
      declare(PSI, "PSI");
      // histos
      for (unsigned int ix = 0; ix < 2; ++ix) book(_h[ix], 1, 1, 1 + ix);
      book(_h[2], 2, 1, 1);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // find the J/psi decays
      static const map<PdgId, unsigned int>& mode = {{22, 1}, {331, 1}, {211, 1}, {-211, 1}};
      DecayedParticles PSI = apply<DecayedParticles>(event, "PSI");
      for (unsigned int ix = 0; ix < PSI.decaying().size(); ++ix) {
        if (!PSI.modeMatches(ix, 4, mode)) continue;
        const Particle& gam = PSI.decayProducts()[ix].at(22)[0];
        double mass = (PSI.decaying()[ix].momentum() - gam.momentum()).mass();
        for (unsigned int ix = 0; ix < 3; ++ix) _h[ix]->fill(mass);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      for (unsigned int ix = 0; ix < 3; ++ix) normalize(_h[ix], 1., false);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h[3];
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESIII_2016_I1437949);

}