Rivet analyses

J/ψ → pp̄π0

Experiment: BESII (BEPC)

Inspire ID: 819937

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 80 (2009) 052004

Beams: * *

Beam energies: ANY

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

Measurement of the mass distributions in the decay J/ψ → pp̄π0. The data were read from the plots in the paper, but is corrected for detector efficiency.

Source code:BESII_2009_I819937.cc

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

namespace Rivet {


  /// @brief J/psi -> p pbar pi0
  class BESII_2009_I819937 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESII_2009_I819937);


    /// @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::K0S);
      psi.addStable(PID::ETA);
      psi.addStable(PID::ETAPRIME);
      declare(psi, "psi");
      for (unsigned int ix = 0; ix < 2; ++ix) book(_h[ix], 1, 1, 1 + ix);
      book(_dalitz, "dalitz", 50, 1., 5., 50, 1., 5.);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId, unsigned int>& mode = {{2212, 1}, {-2212, 1}, {111, 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 Particles& pi0 = psi.decayProducts()[ix].at(111);
        const Particles& pp = psi.decayProducts()[ix].at(2212);
        const Particles& pbar = psi.decayProducts()[ix].at(-2212);
        double mminus = (pbar[0].momentum() + pi0[0].momentum()).mass2();
        double mplus = (pp[0].momentum() + pi0[0].momentum()).mass2();
        _h[0]->fill(sqrt(mplus));
        _h[1]->fill(sqrt(mminus));
        _dalitz->fill(mplus, mminus);
      }
    }


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

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h[2];
    Histo2DPtr _dalitz;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESII_2009_I819937);

}