Rivet analyses

χc(0, 1, 2) → Σ0p̄K+ + c.c

Experiment: BESIII (BEPC)

Inspire ID: 1818254

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 102 (2020) 9, 092006

Beams: * *

Beam energies: ANY

Run details: - Any process producing chi_c originally e+e-

Measurement of the mass distributions in the decays χc(0, 1, 2) → Σ0p̄K+ + c.c. The data were read from the plots in the paper and may not be corrected for efficiency or background.

Source code:BESIII_2020_I1818254.cc

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

namespace Rivet {


  /// @brief  chi_c -> pbar Sigma0 K+
  class BESIII_2020_I1818254 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2020_I1818254);


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

    /// Book histograms and initialise projections before the run
    void init() {
      UnstableParticles ufs = UnstableParticles(Cuts::pid == 20443 or Cuts::pid == 445 or Cuts::pid == 10441);
      declare(ufs, "UFS");
      DecayedParticles chi(ufs);
      chi.addStable(PID::PI0);
      chi.addStable(PID::K0S);
      chi.addStable(PID::ETA);
      chi.addStable(PID::ETAPRIME);
      chi.addStable(PID::SIGMA0);
      chi.addStable(-PID::SIGMA0);
      declare(chi, "chi");
      for (unsigned int ix = 0; ix < 3; ++ix) {
        book(_dalitz[ix], "dalitz_" + toString(ix + 1), 50, 2.5, 7., 50, 1.8, 6.);
        for (unsigned int iy = 0; iy < 3; ++iy) {
          book(_h[ix][iy], 1 + ix, 1, 1 + iy);
        }
      }
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId, unsigned int>& mode = {{-2212, 1}, {3212, 1}, {321, 1}};
      static const map<PdgId, unsigned int>& modeCC = {{2212, 1}, {-3212, 1}, {-321, 1}};
      DecayedParticles chi = apply<DecayedParticles>(event, "chi");
      // loop over particles
      for (unsigned int ix = 0; ix < chi.decaying().size(); ++ix) {
        int sign = 1;
        if (chi.modeMatches(ix, 3, mode)) {
          sign = 1;
        }
        else if (chi.modeMatches(ix, 3, modeCC)) {
          sign = -1;
        }
        else
          continue;
        unsigned int iloc = chi.decaying()[ix].pid() == 10441 ? 0 : chi.decaying()[ix].pid() == 445 ? 2 : 1;
        const Particle& Kp = chi.decayProducts()[ix].at(sign * 321)[0];
        const Particle& pbar = chi.decayProducts()[ix].at(-sign * 2212)[0];
        const Particle& sig = chi.decayProducts()[ix].at(sign * 3212)[0];
        double mpK = (Kp.momentum() + pbar.momentum()).mass2();
        double msigK = (Kp.momentum() + sig.momentum()).mass2();
        double msigp = (sig.momentum() + pbar.momentum()).mass2();
        _h[iloc][0]->fill(sqrt(mpK));
        _h[iloc][1]->fill(sqrt(msigK));
        _h[iloc][2]->fill(sqrt(msigp));
        _dalitz[iloc]->fill(msigK, mpK);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      for (unsigned int ix = 0; ix < 3; ++ix) {
        normalize(_dalitz[ix]);
        for (unsigned int iy = 0; iy < 3; ++iy) {
          normalize(_h[ix][iy], 1., false);
        }
      }
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h[3][3];
    Histo2DPtr _dalitz[3];
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESIII_2020_I1818254);

}