Rivet analyses

Hadronic Mass in J/ψ → γηπ+π−

Experiment: BES (BEPC)

Inspire ID: 498114

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Lett.B 446 (1999) 356-362

Beams: * *

Beam energies: ANY

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

Measurement of the hadronic mass in J/ψ → γηπ+π−. The data were read from figure 2 in the paper and the background given subtracted.

Source code:BES_1999_I498114.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 BES_1999_I498114 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BES_1999_I498114);


    /// @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);
      declare(PSI, "PSI");
      // histos
      book(_h, 1, 1, 1);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // find the J/psi decays
      static const map<PdgId, unsigned int>& mode = {{221, 1}, {211, 1}, {211, 1}, {22, 1}};
      DecayedParticles PSI = apply<DecayedParticles>(event, "PSI");
      // loop over particles
      for (unsigned int ix = 0; ix < PSI.decaying().size(); ++ix) {
        if (!PSI.modeMatches(ix, 4, mode)) continue;
        const Particle& gam = PSI.decayProducts()[0].at(22)[0];
        _h->fill((PSI.decaying()[ix].mom() - gam.mom()).mass());
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      normalize(_h, 1., false);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BES_1999_I498114);

}