Rivet analyses

χc(0, 1, 2) → nKS0Λ̄0 + c.c

Experiment: BESIII (BEPC)

Inspire ID: 1870388

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - JHEP 11 (2021) 217

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) → nKS0Λ̄0 + c.c. The data were read from the plots in the paper and may not be corrected for efficiency or background.

Source code:BESIII_2021_I1870388.cc

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

namespace Rivet {


  /// @brief chi_c -> n K0S Lambdabar +cc
  class BESIII_2021_I1870388 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2021_I1870388);


    /// @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::LAMBDA);
      chi.addStable(-PID::LAMBDA);
      declare(chi, "chi");
      // histograms
      for (unsigned int ix = 0; ix < 3; ++ix) {
        book(_dalitz[ix], "dalitz_" + toString(ix + 1), 50, 2., 7., 50, 2., 6.2);
        for (unsigned int iy = 0; iy < 3; ++iy) book(_h[ix][iy], ix + 1, 1, iy + 1);
      }
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId, unsigned int>& mode = {{2112, 1}, {-3122, 1}, {310, 1}};
      static const map<PdgId, unsigned int>& modeCC = {{-2112, 1}, {3122, 1}, {310, 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& KS0 = chi.decayProducts()[ix].at(310)[0];
        const Particle& nn = chi.decayProducts()[ix].at(sign * 2112)[0];
        const Particle& lbar = chi.decayProducts()[ix].at(-sign * 3122)[0];
        double mnLam = (nn.momentum() + lbar.momentum()).mass2();
        double mnK = (nn.momentum() + KS0.momentum()).mass2();
        double mKLam = (lbar.momentum() + KS0.momentum()).mass2();
        _h[iloc][0]->fill(sqrt(mnLam));
        _h[iloc][1]->fill(sqrt(mnK));
        _h[iloc][2]->fill(sqrt(mKLam));
        _dalitz[iloc]->fill(mKLam, mnK);
      }
    }


    /// 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]);
      }
    }

    /// @}


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


  RIVET_DECLARE_PLUGIN(BESIII_2021_I1870388);

}