1// -*- C++ -*-
 2#include "Rivet/Analysis.hh"
 3#include "Rivet/Projections/UnstableParticles.hh"
 4
 5namespace Rivet {
 6
 7
 8  /// @brief D_s -> eta, eta' semi-leptonic
 9  class BESIII_2023_I2679776 : public Analysis {
10  public:
11
12    /// Constructor
13    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2023_I2679776);
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      // histograms
24      for (unsigned int ix=0; ix<2; ++ix) {
25        for (unsigned int iy=0; iy<2; ++iy) {
26          book(_h[ix][iy], ix+1, 1, iy+1);
27        }
28      }
29      // counter for normalization
30      book(_nDs, "TMP/nDs");
31    }
32
33    // Calculate the Q2 using mother and daugher meson
34    double q2(const Particle& B, int mesonID) {
35      FourMomentum q = B.mom() - select(B.children(), Cuts::pid==mesonID)[0];
36      return q*q;
37    }
38
39    // Check for explicit decay into pdgids
40    bool isSemileptonicDecay(const Particle& mother, const vector<int>& ids) {
41      // Trivial check to ignore any other decays but the one in question modulo photons
42      const Particles children = mother.children(Cuts::pid!=PID::PHOTON);
43      if (children.size() != ids.size()) return false;
44      // Check for the explicit decay
45      return all(ids, [&](int i){return count(children, hasPID(i))==1;});
46    }
47
48    /// Perform the per-event analysis
49    void analyze(const Event& event) {
50      // Loop over Ds mesons
51      for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles()) {
52        _nDs->fill();
53        if (isSemileptonicDecay(p, {PID::ETA, PID::ANTIMUON, PID::NU_MU})) {
54          _h[0][0]->fill(q2(p, PID::ETA));
55          _h[0][1]->fill(q2(p, PID::ETA));
56        }
57        else if (isSemileptonicDecay(p, {PID::ETAPRIME, PID::ANTIMUON, PID::NU_MU})) {
58          _h[1][0]->fill(q2(p, PID::ETAPRIME));
59          _h[1][1]->fill(q2(p, PID::ETAPRIME));
60        }
61      }
62    }
63
64
65    /// Normalise histograms etc., after the run
66    void finalize() {
67      // D_s lifetime pdg2023 (ns)
68      const double tau = 504e-6;
69      for (unsigned int ix=0; ix<2; ++ix) {
70        scale(_h[ix], 1./tau/ *_nDs);
71      }
72    }
73
74    /// @}
75
76
77    /// @name Histograms
78    /// @{
79    CounterPtr _nDs;
80    Histo1DPtr _h[2][2];
81    /// @}
82
83
84  };
85
86
87  RIVET_DECLARE_PLUGIN(BESIII_2023_I2679776);
88
89}