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);

}