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BESIII_2020_I1800404

Charged particle multiplicity distributions in $J/\psi$ and $\chi_{c0,1,2}$ decays
Experiment: BESIII (BEPC)
Inspire ID: 1800404
Status: VALIDATED
Authors:
  • Peter Richardson
References: 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 $J/\psi$ and $\chi_{c0,1,2}$ decays by the BES collaboration.

Source code: BESIII_2020_I1800404.cc
 1// -*- C++ -*-
 2#include "Rivet/Analysis.hh"
 3#include "Rivet/Projections/UnstableParticles.hh"
 4
 5namespace Rivet {
 6
 7
 8  /// @brief J/Psi chi_c charged particle multiplicities
 9  class BESIII_2020_I1800404 : public Analysis {
10  public:
11
12    /// Constructor
13    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2020_I1800404);
14
15
16    /// @name Analysis methods
17    ///@{
18
19    /// Book histograms and initialise projections before the run
20    void init() {
21      // Initialise and register projections
22      declare(UnstableParticles(Cuts::pid==443 or Cuts::pid==445 or Cuts::pid==10441 or Cuts::pid==20443),"UFS");
23      // histograms
24      book(_h_chi0,1,1,1);
25      book(_h_chi1,1,1,2);
26      book(_h_chi2,1,1,3);
27      book(_h_jpsi[0],2,1,1);
28      book(_h_jpsi[1],2,1,2);
29    }
30
31    void findChildren(const Particle & p, int & nCharged) {
32      for( const Particle &child : p.children()) {
33	if(child.children().empty()) {
34	  if(PID::isCharged(child.pid())) ++nCharged;
35	}
36	else
37	  findChildren(child,nCharged);
38      }
39    }
40
41    /// Perform the per-event analysis
42    void analyze(const Event& event) {
43      // loop over particles
44      for( const Particle & p : apply<UnstableParticles>(event, "UFS").particles()) {
45	// skip radiative modes
46	if(p.children().size()==2) {
47	  if(p.children()[0].pid()==PID::GAMMA) {
48	    if(p.children()[1].pid()==PID::GAMMA ||
49	       p.children()[1].pid()==PID::JPSI) continue;
50	  }
51	  if(p.children()[1].pid()==PID::GAMMA) {
52	    if(p.children()[0].pid()==PID::GAMMA ||
53	       p.children()[0].pid()==PID::JPSI) continue;
54	  }
55	}
56	// get the charged particle multiplicity
57	int nCharged(0);
58	findChildren(p,nCharged);
59	if(p.pid()==PID::JPSI) {
60	  _h_jpsi[0]->fill(nCharged);
61	  _h_jpsi[1]->fill(nCharged);
62	}
63	else if(p.pid()==10441)
64	  _h_chi0->fill(nCharged);
65	else if(p.pid()==20443)
66	  _h_chi1->fill(nCharged);
67	else if(p.pid()==445)
68	  _h_chi2->fill(nCharged);
69      }
70    }
71
72
73    /// Normalise histograms etc., after the run
74    void finalize() {
75      // percentage and bin width
76      normalize(_h_jpsi[0],200.);
77      normalize(_h_jpsi[1],200.);
78      normalize(_h_chi0   ,200.);
79      normalize(_h_chi1   ,200.);
80      normalize(_h_chi2   ,200.);
81    }
82
83    ///@}
84
85
86    /// @name Histograms
87    ///@{
88    Histo1DPtr _h_jpsi[2],_h_chi0,_h_chi1,_h_chi2;
89    ///@}
90
91
92  };
93
94
95  RIVET_DECLARE_PLUGIN(BESIII_2020_I1800404);
96
97}