Rivet analyses

J/ψ and ψ(2S) → pp̄η′

Experiment: BESIII (BEPC)

Inspire ID: 1709205

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 99 (2019) 3, 032006

Beams: * *

Beam energies: ANY

Run details: - Any process producing J/psi or psi(2S) originally e+e-

Measurement of the mass distributions in the decay J/ψ or ψ(2S) → pp̄η′. The data were read from the plots in the paper. It is also not clear that any resolution effects have been unfolded.

Source code:BESIII_2019_I1709205.cc

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


namespace Rivet {


  /// @brief J/psi psi(2S) -> p pbar eta'
  class BESIII_2019_I1709205 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2019_I1709205);


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

    /// Book histograms and initialise projections before the run
    void init() {
      UnstableParticles ufs = UnstableParticles(Cuts::pid == 443 or Cuts::pid == 100443);
      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) {
        for (unsigned int iy = 0; iy < 6; ++iy) {
          book(_h[ix][iy], 1 + ix, 1, 1 + iy);
        }
      }
      book(_dalitz[0], "dalitz_1", 50, 3., 8., 50, 3., 8.);
      book(_dalitz[1], "dalitz_2", 50, 3.5, 5., 50, 3.5, 5.);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId, unsigned int>& mode = {{2212, 1}, {-2212, 1}, {331, 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& etap = psi.decayProducts()[ix].at(331);
        const Particles& pp = psi.decayProducts()[ix].at(2212);
        const Particles& pbar = psi.decayProducts()[ix].at(-2212);
        double mminus = (pbar[0].momentum() + etap[0].momentum()).mass2();
        double mplus = (pp[0].momentum() + etap[0].momentum()).mass2();
        double mneut = (pp[0].momentum() + pbar[0].momentum()).mass2();
        unsigned int iloc = psi.decaying()[ix].pid() == 443 ? 1 : 0;
        for (unsigned int ix = 0; ix < 4; ix += 3) {
          _h[iloc][ix + 2]->fill(sqrt(mneut));
          _h[iloc][ix + 0]->fill(sqrt(mplus));
          _h[iloc][ix + 1]->fill(sqrt(mminus));
        }
        _dalitz[iloc]->fill(mplus, mminus);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      for (unsigned int ix = 0; ix < 2; ++ix) {
        normalize(_dalitz[ix]);
        for (unsigned int iy = 0; iy < 6; ++iy) {
          normalize(_h[ix][iy]);
        }
      }
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h[2][6];
    Histo2DPtr _dalitz[2];
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESIII_2019_I1709205);

}