Rivet analyses

χc1 → ηπ+π−

Experiment: BESIII (BEPC)

Inspire ID: 1490896

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 95 (2017) 3, 032002

Beams: * *

Beam energies: ANY

Run details: - Any process producing chi_c1

Measurement of the mass distributions in the decays χc1 → ηπ+π−. The data were read from the plots in the paper and may not be corrected for efficiency.

Source code:BESIII_2017_I1490896.cc

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

namespace Rivet {


  /// @brief  chi_c1 -> eta pi+pi-
  class BESIII_2017_I1490896 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2017_I1490896);


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

    /// Book histograms and initialise projections before the run
    void init() {
      UnstableParticles ufs = UnstableParticles(Cuts::pid == 20443);
      declare(ufs, "UFS");
      DecayedParticles chi(ufs);
      chi.addStable(PID::PI0);
      chi.addStable(PID::K0S);
      chi.addStable(PID::ETA);
      declare(chi, "chi");
      for (unsigned int ix = 0; ix < 2; ++ix) book(_h[ix], 1, 1, ix + 1);
      book(_dalitz, "dalitz", 50, 0., 12., 50, 0., 9.);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId, unsigned int>& mode1 = {{221, 1}, {211, 1}, {-211, 1}};
      DecayedParticles chi = apply<DecayedParticles>(event, "chi");
      // loop over particles
      for (unsigned int ix = 0; ix < chi.decaying().size(); ++ix) {
        if (chi.modeMatches(ix, 3, mode1)) {
          const Particle& eta = chi.decayProducts()[ix].at(221)[0];
          const Particle& pim = chi.decayProducts()[ix].at(-211)[0];
          const Particle& pip = chi.decayProducts()[ix].at(211)[0];
          double m1 = (pip.momentum() + pim.momentum()).mass2();
          double m2 = (eta.momentum() + pip.momentum()).mass2();
          double m3 = (eta.momentum() + pim.momentum()).mass2();
          _dalitz->fill(m2, m1);
          _h[1]->fill(sqrt(m1));
          _h[0]->fill(sqrt(m2));
          _h[0]->fill(sqrt(m3));
        }
      }
    }


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

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


  RIVET_DECLARE_PLUGIN(BESIII_2017_I1490896);

}