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BESIII_2018_I1697377

$J/\psi\to e^+e^-\eta$ decays
Experiment: BESIII ()
Inspire ID: 1697377
Status: VALIDATED
Authors:
  • Peter Richardson
References:
  • Phys.Rev. D99 (2019) no.1, 012006
Beams: * *
Beam energies: ANY
Run details:
  • Events with J/psi decays, either particle guns or collisions.

Differential decay rates for $J/\psi\to e^+e^-\eta$ decays.

Source code: BESIII_2018_I1697377.cc
 1// -*- C++ -*-
 2#include "Rivet/Analysis.hh"
 3#include "Rivet/Projections/UnstableParticles.hh"
 4
 5namespace Rivet {
 6
 7
 8  /// @brief Add a short analysis description here
 9  class BESIII_2018_I1697377 : public Analysis {
10  public:
11
12    /// Constructor
13    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2018_I1697377);
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(), "UFS");
23      // Book histograms
24      book(_h_m, 1, 1, 1);
25    }
26
27    void findDecayProducts(const Particle & mother, unsigned int & nstable, unsigned int & neta, 
28                           unsigned int & nep, unsigned int & nem, FourMomentum & ptot) {
29      for(const Particle & p : mother.children()) {
30        int id = p.pid();
31        if (id == PID::EMINUS ) {
32	  ++nem;
33          ++nstable;
34	  ptot += p.momentum();
35	}
36        else if (id == PID::EPLUS) {
37          ++nep;
38          ++nstable;
39	  ptot += p.momentum();
40        }
41        else if (id == PID::ETA) {
42	  ++neta;
43          ++nstable;
44        }
45        else if ( !p.children().empty() ) {
46          findDecayProducts(p, nstable, neta,nep,nem,ptot);
47        }
48        else
49          ++nstable;
50      }
51    }
52
53    /// Perform the per-event analysis
54    void analyze(const Event& event) {
55
56      // Loop over J/psi mesons
57      for (const Particle& p :  apply<UnstableParticles>(event, "UFS").particles(Cuts::pid==443)) {
58	unsigned nstable(0),neta(0),nep(0),nem(0);
59	FourMomentum ptot;
60	findDecayProducts(p,nstable,neta,nep,nem,ptot);
61	if(nstable==3 && nem==1 && nem==1 && neta==1) {
62	  _h_m->fill(ptot.mass());
63	}
64      }
65
66    }
67
68
69    /// Normalise histograms etc., after the run
70    void finalize() {
71
72      normalize(_h_m); // normalize to unity
73
74    }
75
76    //@}
77
78
79    /// @name Histograms
80    //@{
81    Histo1DPtr _h_m;
82    //@}
83
84
85  };
86
87
88  // The hook for the plugin system
89  RIVET_DECLARE_PLUGIN(BESIII_2018_I1697377);
90
91
92}