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 J/psi -> gamma eta pi+ pi-
10  class BES_1999_I498114 : public Analysis {
11  public:
12
13    /// Constructor
14    RIVET_DEFAULT_ANALYSIS_CTOR(BES_1999_I498114);
15
16
17    /// @name Analysis methods
18    /// @{
19
20    /// Book histograms and initialise projections before the run
21    void init() {
22      // Initialise and register projections
23      UnstableParticles ufs = UnstableParticles(Cuts::abspid==443);
24      declare(ufs, "UFS");
25      DecayedParticles PSI(ufs);
26      PSI.addStable(PID::ETA);
27      declare(PSI, "PSI");
28      // histos
29      book(_h,1,1,1);
30    }
31
32
33    /// Perform the per-event analysis
34    void analyze(const Event& event) {
35      // find the J/psi decays
36      static const map<PdgId,unsigned int> & mode = { { 221,1}, { 211,1}, { 211,1}, { 22,1}};
37      DecayedParticles PSI = apply<DecayedParticles>(event, "PSI");
38      // loop over particles
39      for (unsigned int ix=0; ix<PSI.decaying().size(); ++ix) {
40        if (!PSI.modeMatches(ix,4,mode)) continue;
41        const Particle & gam = PSI.decayProducts()[0].at( 22)[0];
42        _h->fill((PSI.decaying()[ix].mom()-gam.mom()).mass());
43      }
44    }
45
46
47    /// Normalise histograms etc., after the run
48    void finalize() {
49      normalize(_h,1.,false);
50    }
51
52    /// @}
53
54
55    /// @name Histograms
56    /// @{
57    Histo1DPtr _h;
58    /// @}
59
60
61  };
62
63
64  RIVET_DECLARE_PLUGIN(BES_1999_I498114);
65
66}