Rivet analyses

χc(1, 2) → η′K+K−

Experiment: BESIII ()

Inspire ID: 1280710

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 89 (2014) 7, 074030

Beams: * *

Beam energies: ANY

Run details: - Any process producing chi_c1 or chi_c2

Measurement of the mass distributions in the decays χc(1, 2) → η′K+K−. The data were read from the plots in the paper and may not be corrected for efficiency.

Source code:BESIII_2014_I1280710.cc

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

namespace Rivet {


  /// @brief chi_c -> eta' K+K-
  class BESIII_2014_I1280710 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2014_I1280710);


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

    /// Book histograms and initialise projections before the run
    void init() {
      UnstableParticles ufs = UnstableParticles(Cuts::pid == 20443 or Cuts::pid == 445);
      declare(ufs, "UFS");
      DecayedParticles chi(ufs);
      chi.addStable(PID::PI0);
      chi.addStable(PID::K0S);
      chi.addStable(PID::ETA);
      chi.addStable(PID::ETAPRIME);
      declare(chi, "chi");
      for (unsigned int ix = 0; ix < 4; ++ix)
        for (unsigned int iy = 0; iy < 2; ++iy) book(_h[ix][iy], 1 + ix, 1, 1 + iy);
      for (unsigned int ix = 0; ix < 2; ++ix)
        book(_dalitz[ix], "dalitz_" + toString(ix + 1), 50, 2., 10., 50, 2., 10.);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId, unsigned int>& mode1 = {{331, 1}, {321, 1}, {-321, 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)) continue;
        unsigned int iloc = chi.decaying()[ix].pid() == 445 ? 1 : 0;
        const Particle& eta = chi.decayProducts()[ix].at(331)[0];
        const Particle& Km = chi.decayProducts()[ix].at(-321)[0];
        const Particle& Kp = chi.decayProducts()[ix].at(321)[0];
        double m1 = (Kp.momentum() + Km.momentum()).mass2();
        double m2 = (eta.momentum() + Kp.momentum()).mass2();
        double m3 = (eta.momentum() + Km.momentum()).mass2();
        _dalitz[iloc]->fill(m2, m3);
        for (unsigned int ix = 0; ix < 2; ++ix) {
          _h[2 * iloc + ix][0]->fill(sqrt(m1));
          _h[2 * iloc + ix][1]->fill(sqrt(m2));
          _h[2 * iloc + ix][1]->fill(sqrt(m3));
        }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      for (unsigned int iy = 0; iy < 2; ++iy) {
        normalize(_dalitz[iy]);
        for (unsigned int ix = 0; ix < 4; ++ix) normalize(_h[ix][iy], 1., false);
      }
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h[4][2];
    Histo2DPtr _dalitz[2];
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESIII_2014_I1280710);

}