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BESIII_2015_I1364494

$\eta^\prime\to e^+e^-\gamma$ decays
Experiment: BESIII (BEPC)
Inspire ID: 1364494
Status: VALIDATED
Authors:
  • Peter Richardson
References:
  • Phys.Rev. D92 (2015) 012001, 2015
Beams: * *
Beam energies: ANY
Run details:
  • Events with eta prime decays, either particle guns or collisions.

Differential decay rates for $\eta^\prime\to e^+e^-\gamma$ decays

Source code: BESIII_2015_I1364494.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_2015_I1364494 : public Analysis {
10  public:
11
12    /// Constructor
13    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2015_I1364494);
14
15
16    /// @name Analysis methods
17    //@{
18
19    /// Book histograms and initialise projections before the run
20    void init() {
21
22      // Initialise and register projections
23      declare(UnstableParticles(), "UFS");
24
25      // Book histograms
26      book(_h_m, 1, 1, 3);
27      book(_netap, "TMP/netap");
28    }
29    
30    void findDecayProducts(const Particle & mother, unsigned int & nstable, unsigned int & ngamma, 
31                           unsigned int & nep, unsigned int & nem, FourMomentum & ptot) {
32      for(const Particle & p : mother.children()) {
33        int id = p.pid();
34        if (id == PID::EMINUS ) {
35	  ++nem;
36          ++nstable;
37	  ptot += p.momentum();
38	}
39        else if (id == PID::EPLUS) {
40          ++nep;
41          ++nstable;
42	  ptot += p.momentum();
43        }
44        else if ( !p.children().empty() ) {
45          findDecayProducts(p, nstable, ngamma,nep,nem,ptot);
46        }
47        else if (id == PID::GAMMA) {
48	  ++ngamma;
49          ++nstable;
50        }
51        else
52          ++nstable;
53      }
54    }
55
56
57    /// Perform the per-event analysis
58    void analyze(const Event& event) {
59
60      // Loop over eta' mesons
61      for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles(Cuts::pid==331)) {
62	unsigned nstable(0),ngamma(0),nep(0),nem(0);
63	FourMomentum ptot;
64	findDecayProducts(p,nstable,ngamma,nep,nem,ptot);
65	if(nstable==3 && nem==1 && nem==1 && ngamma==1)
66	  _h_m->fill(ptot.mass());
67	else if(nstable==2 &&ngamma==2)
68	  _netap->fill();
69      }
70    }
71
72
73    /// Normalise histograms etc., after the run
74    void finalize() {
75
76      // divide by no so BR and mult by bin width
77      // and 100 as in %
78      scale(_h_m,1./_netap->sumW()*0.1*100.);
79
80    }
81
82    //@}
83
84
85    /// @name Histograms
86    //@{
87    Histo1DPtr _h_m;
88    CounterPtr _netap;
89    //@}
90
91
92  };
93
94
95  // The hook for the plugin system
96  RIVET_DECLARE_PLUGIN(BESIII_2015_I1364494);
97
98
99}