1// -*- C++ -*-
 2#include "Rivet/Analysis.hh"
 3#include "Rivet/Projections/UnstableParticles.hh"
 4#include "Rivet/Projections/DecayedParticles.hh"
 5
 6namespace Rivet {
 7
 8
 9  /// @brief psi(2S) -> eta_c e+e-
10  class BESIII_2022_I2141748 : public Analysis {
11  public:
12
13    /// Constructor
14    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2022_I2141748);
15
16
17    /// @name Analysis methods
18    /// @{
19
20    /// Book histograms and initialise projections before the run
21    void init() {
22      UnstableParticles ufs = UnstableParticles(Cuts::abspid==PID::PSI2S);
23      declare(ufs, "UFS");
24      DecayedParticles psi(ufs);
25      psi.addStable(PID::PI0);
26      psi.addStable(PID::ETAC);
27      declare(psi, "PSI");
28      book(_h, 1, 1, 1);
29    }
30
31
32    /// Perform the per-event analysis
33    void analyze(const Event& event) {
34      // define the decay mode
35      static const map<PdgId,unsigned int> & mode   = { {PID::ETAC,1},{ 11,1}, { -11,1}};
36      DecayedParticles psi = apply<DecayedParticles>(event, "PSI");
37      // loop over particles
38      for(unsigned int ix=0;ix<psi.decaying().size();++ix) {
39	if(!psi.modeMatches(ix,3,mode)) continue;
40	const Particle & em = psi.decayProducts()[ix].at( 11)[0];
41	const Particle & ep = psi.decayProducts()[ix].at(-11)[0];
42	_h->fill((ep.momentum()+em.momentum()).mass());
43      }
44    }
45
46
47    /// Normalise histograms etc., after the run
48    void finalize() {
49      normalize(_h);
50    }
51
52    /// @}
53
54
55    /// @name Histograms
56    /// @{
57    Histo1DPtr _h;
58    /// @}
59
60
61  };
62
63
64  RIVET_DECLARE_PLUGIN(BESIII_2022_I2141748);
65
66}