1// -*- C++ -*-
 2#include "Rivet/Analysis.hh"
 3#include "Rivet/Projections/UnstableParticles.hh"
 4
 5namespace Rivet {
 6
 7
 8  /// @brief D_s -> f0 e+ nu_e
 9  class BESIII_2023_I2645182 : public Analysis {
10  public:
11
12    /// Constructor
13    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2023_I2645182);
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==431), "UFS");
23      // histos
24      book(_h,1,1,1);
25      book(_nDs, "TMP/nDs");
26    }
27
28    // Check for explicit decay into pdgids
29    bool isSemileptonicDecay(const Particle& mother, vector<int> ids) {
30      // Trivial check to ignore any other decays but the one in question modulo photons
31      const Particles children = mother.children(Cuts::pid!=PID::PHOTON);
32      if (children.size()!=ids.size()) return false;
33      // Check for the explicit decay
34      return all(ids, [&](int i){return count(children, hasPID(i))==1;});
35    }
36
37    /// Perform the per-event analysis
38    void analyze(const Event& event) {
39      static const int mesonID=9010221;
40      // Loop over Ds mesons
41      for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles()) {
42        _nDs->fill();
43        Particle f0;
44        if (isSemileptonicDecay(p, {mesonID, PID::POSITRON, PID::NU_E})) {
45          f0  = select(p.children(), Cuts::pid==mesonID)[0];
46          if (f0.children().size()==2 &&
47              f0.children()[1].pid() == -f0.children()[0].pid() &&
48              f0.children()[0].abspid()==211) {
49            _h->fill((p.mom()-f0.mom()).mass2());
50          }
51        }
52      }
53    }
54
55
56    /// Normalise histograms etc., after the run
57    void finalize() {
58      // D_s lifetime pdg2022 (ns)
59      const double tau = 504e-6;
60      scale(_h,1./tau/ *_nDs);
61    }
62
63    /// @}
64
65
66    /// @name Histograms
67    /// @{
68    Histo1DPtr _h;
69    CounterPtr _nDs;
70    /// @}
71
72
73  };
74
75
76  RIVET_DECLARE_PLUGIN(BESIII_2023_I2645182);
77
78}