Rivet analyses

ηπ0 mass distribution in J/ψ → γηπ0

Experiment: BESIII (BEPC)

Inspire ID: 1484158

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 94 (2016) 7, 072005

Beams: * *

Beam energies: ANY

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

Measurement of the ηπ0 mass distribution in J/ψ → γηπ0 decays. The data were read from the plots in the paper and the backgrounds given subtracted, although acceptance/efficiency may not be corrected.

Source code:BESIII_2016_I1484158.cc

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

namespace Rivet {


  /// @brief J/psi -> gamma eta pi0
  class BESIII_2016_I1484158 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2016_I1484158);


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

    /// Book histograms and initialise projections before the run
    void init() {
      UnstableParticles ufs = UnstableParticles(Cuts::pid == 443);
      declare(ufs, "UFS");
      DecayedParticles psi(ufs);
      psi.addStable(PID::PI0);
      psi.addStable(PID::ETA);
      declare(psi, "psi");
      //histograms
      book(_h, 1, 1, 1);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId, unsigned int>& mode = {{221, 1}, {111, 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, 3, mode)) continue;
        const Particle& eta = psi.decayProducts()[ix].at(221)[0];
        const Particle& pi0 = psi.decayProducts()[ix].at(111)[0];
        _h->fill((eta.momentum() + pi0.momentum()).mass());
      }
    }


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

    /// @}


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


  RIVET_DECLARE_PLUGIN(BESIII_2016_I1484158);

}