Rivet analyses

Mass distributions in χcJ → pn̄π− and pn̄π−π0

Experiment: BESIII (BEPC)

Inspire ID: 1128258

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 86 (2012) 052011

Beams: * *

Beam energies: ANY

Run details: - Any process producing chi_c0,1,2

Measurement of the mass distributions in the decays χcJ → pn̄π− and pn̄π−π0. The data were read from the plots in the paper and may not be corrected for backgrounds and efficiency.

Source code:BESIII_2012_I1128258.cc

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

namespace Rivet {


  /// @brief chi_c -> p nbar pi- p nbar pi- pi0
  class BESIII_2012_I1128258 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2012_I1128258);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // projections
      UnstableParticles ufs = UnstableParticles(Cuts::pid == 10441 || Cuts::pid == 445 || Cuts::pid == 20444);
      declare(ufs, "UFS");
      DecayedParticles chi(ufs);
      chi.addStable(PID::PI0);
      declare(chi, "chi");
      // histograms
      for (unsigned int ix = 0; ix < 3; ++ix) book(_h[ix], 1, 1, 1 + ix);
      book(_h[3], 2, 1, 1);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId, unsigned int>& mode1 = {{2212, 1}, {-2112, 1}, {-211, 1}};
      static const map<PdgId, unsigned int>& mode1CC = {{-2212, 1}, {2112, 1}, {211, 1}};
      static const map<PdgId, unsigned int>& mode2 = {{2212, 1}, {-2112, 1}, {-211, 1}, {111, 1}};
      static const map<PdgId, unsigned int>& mode2CC = {{-2212, 1}, {2112, 1}, {211, 1}, {111, 1}};
      DecayedParticles chi = apply<DecayedParticles>(event, "chi");
      // loop over particles
      for (unsigned int ix = 0; ix < chi.decaying().size(); ++ix) {
        int mode = -1, sign = 0;
        if (chi.decaying()[ix].pid() == 10441) {
          if (chi.modeMatches(ix, 3, mode1)) {
            mode = 0;
            sign = 1;
          }
          else if (chi.modeMatches(ix, 3, mode1CC)) {
            mode = 0;
            sign = -1;
          }
        }
        if (mode == 0) {
          const Particle& pim = chi.decayProducts()[ix].at(-211 * sign)[0];
          const Particle& pp = chi.decayProducts()[ix].at(2212 * sign)[0];
          const Particle& nbar = chi.decayProducts()[ix].at(-2112 * sign)[0];
          _h[0]->fill((pp.momentum() + pim.momentum()).mass());
          _h[1]->fill((nbar.momentum() + pim.momentum()).mass());
          _h[2]->fill((pp.momentum() + nbar.momentum()).mass());
          continue;
        }
        else if (chi.modeMatches(ix, 4, mode2)) {
          mode = 1;
          sign = 1;
        }
        else if (chi.modeMatches(ix, 4, mode2CC)) {
          mode = 1;
          sign = -1;
        }
        else
          continue;
        const Particle& pim = chi.decayProducts()[ix].at(-211 * sign)[0];
        const Particle& pi0 = chi.decayProducts()[ix].at(111)[0];
        _h[3]->fill((pim.momentum() + pi0.momentum()).mass());
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      for (unsigned int ix = 0; ix < 4; ++ix) normalize(_h[ix]);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h[4];
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESIII_2012_I1128258);

}