1// -*- C++ -*-
 2#include "Rivet/Analysis.hh"
 3#include "Rivet/Projections/UnstableParticles.hh"
 4
 5namespace Rivet {
 6
 7
 8  /// @brief q^2 in D+ -> eta e+ nu_e
 9  class BESIII_2018_I1662660 : public Analysis {
10  public:
11
12    /// Constructor
13    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2018_I1662660);
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_q2, 1, 1, 1);
27    }
28
29    // Calculate the Q2 using mother and daugher meson
30    double q2(const Particle& B, int mesonID) {
31      FourMomentum q = B.mom() - filter_select(B.children(), Cuts::pid==mesonID)[0];
32      return q*q;
33    }
34
35    // Check for explicit decay into pdgids
36    bool isSemileptonicDecay(const Particle& mother, vector<int> ids) {
37      // Trivial check to ignore any other decays but the one in question modulo photons
38      const Particles children = mother.children(Cuts::pid!=PID::PHOTON);
39      if (children.size()!=ids.size()) return false;
40      // Check for the explicit decay
41      return all(ids, [&](int i){return count(children, hasPID(i))==1;});
42    }
43
44    /// Perform the per-event analysis
45    void analyze(const Event& event) {
46      // Loop over D+ mesons 
47      for(const Particle& p : apply<UnstableParticles>(event, "UFS").particles(Cuts::pid==PID::DPLUS )) {
48        if(p.pid()==PID::DPLUS && isSemileptonicDecay(p, {PID::ETA, PID::EPLUS, PID::NU_E}) ) {
49	  _h_q2->fill(q2(p, PID::ETA));
50        }
51      }
52    }
53
54
55    /// Normalise histograms etc., after the run
56    void finalize() {
57      normalize(_h_q2);
58    }
59
60    ///@}
61
62
63    /// @name Histograms
64    ///@{
65    Histo1DPtr _h_q2;
66    ///@}
67
68
69  };
70
71
72  RIVET_DECLARE_PLUGIN(BESIII_2018_I1662660);
73
74}