Rivet analyses

Charged particle multiplicity distributions in J/ψ and χc0, 1, 2 decays

Experiment: BESIII (BEPC)

Inspire ID: 1800404

Status: VALIDATED

Authors: - Peter Richardson

References: - arXiv: 2006.05588

Beams: * *

Beam energies: ANY

Run details: - Any process producing J/Psi, and chi_{0,1,2}c, originally e+e-

Measurement of the charged particle multiplicity distributions in J/ψ and χc0, 1, 2 decays by the BES collaboration.

Source code:BESIII_2020_I1800404.cc

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

namespace Rivet {


  /// @brief J/Psi chi_c charged particle multiplicities
  class BESIII_2020_I1800404 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2020_I1800404);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(UnstableParticles(Cuts::pid == 443 or Cuts::pid == 445 or Cuts::pid == 10441
                                or Cuts::pid == 20443),
              "UFS");
      // histograms
      book(_h_chi0, 1, 1, 1);
      book(_h_chi1, 1, 1, 2);
      book(_h_chi2, 1, 1, 3);
      book(_h_jpsi[0], 2, 1, 1);
      book(_h_jpsi[1], 2, 1, 2);
    }

    void findChildren(const Particle& p, int& nCharged) {
      for (const Particle& child : p.children()) {
        if (child.children().empty()) {
          if (PID::isCharged(child.pid())) ++nCharged;
        }
        else
          findChildren(child, nCharged);
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // loop over particles
      for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles()) {
        // skip radiative modes
        if (p.children().size() == 2) {
          if (p.children()[0].pid() == PID::GAMMA) {
            if (p.children()[1].pid() == PID::GAMMA || p.children()[1].pid() == PID::JPSI) continue;
          }
          if (p.children()[1].pid() == PID::GAMMA) {
            if (p.children()[0].pid() == PID::GAMMA || p.children()[0].pid() == PID::JPSI) continue;
          }
        }
        // get the charged particle multiplicity
        int nCharged(0);
        findChildren(p, nCharged);
        if (p.pid() == PID::JPSI) {
          _h_jpsi[0]->fill(nCharged);
          _h_jpsi[1]->fill(nCharged);
        }
        else if (p.pid() == 10441)
          _h_chi0->fill(nCharged);
        else if (p.pid() == 20443)
          _h_chi1->fill(nCharged);
        else if (p.pid() == 445)
          _h_chi2->fill(nCharged);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      // percentage and bin width
      normalize(_h_jpsi[0], 100.);
      normalize(_h_jpsi[1], 100.);
      normalize(_h_chi0, 100.);
      normalize(_h_chi1, 100.);
      normalize(_h_chi2, 100.);
    }

    /// @}


    /// @name Histograms
    /// @{
    BinnedHistoPtr<int> _h_jpsi[2], _h_chi0, _h_chi1, _h_chi2;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESIII_2020_I1800404);

}