1// -*- C++ -*-
 2#include "Rivet/Analysis.hh"
 3#include "Rivet/Projections/UnstableParticles.hh"
 4
 5namespace Rivet {
 6
 7
 8  /// @brief Differential decay rates for $D^+\to \{\bar{K}^0,\pi^0\} e^+\nu_e$ from BES
 9  class BESIII_2017_I1519425 : public Analysis {
10  public:
11
12    /// Constructor
13    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2017_I1519425);
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_K , 1, 1, 1);
27      book(_h_q2_pi, 2, 1, 1);
28
29    }
30
31    // Calculate the Q2 using mother and daugher meson
32    double q2(const Particle& B, int mesonID) {
33      FourMomentum q = B.mom() - select(B.children(), Cuts::pid==mesonID)[0];
34      return q*q;
35    }
36
37    // Check for explicit decay into pdgids
38    bool isSemileptonicDecay(const Particle& mother, vector<int> ids) {
39      // Trivial check to ignore any other decays but the one in question modulo photons
40      const Particles children = mother.children(Cuts::pid!=PID::PHOTON);
41      if (children.size()!=ids.size()) return false;
42      // Check for the explicit decay
43      return all(ids, [&](int i){return count(children, hasPID(i))==1;});
44    }
45
46    /// Perform the per-event analysis
47    void analyze(const Event& event) {
48
49      // Loop over D+/- mesons
50      for (const Particle& p :  apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid==PID::DPLUS)) {
51        if (isSemileptonicDecay(p, {PID::PI0, PID::POSITRON, PID::NU_E}) ||
52            isSemileptonicDecay(p, {PID::PI0, PID::ELECTRON, PID::NU_EBAR})) {
53          _h_q2_pi->fill(q2(p, PID::PI0));
54        }
55        else if(isSemileptonicDecay(p, {-311, PID::POSITRON, PID::NU_E})) {
56          _h_q2_K ->fill(q2(p, -311));
57        }
58        else if(isSemileptonicDecay(p, { 311, PID::ELECTRON, PID::NU_EBAR})) {
59          _h_q2_K ->fill(q2(p, 311));
60        }
61        else if(isSemileptonicDecay(p, {PID::K0S, PID::POSITRON, PID::NU_E}) ||
62                isSemileptonicDecay(p, {PID::K0S, PID::ELECTRON, PID::NU_EBAR})) {
63          _h_q2_K ->fill(q2(p, PID::K0S));
64        }
65        else if(isSemileptonicDecay(p, {PID::K0L, PID::POSITRON, PID::NU_E}) ||
66                isSemileptonicDecay(p, {PID::K0L, PID::ELECTRON, PID::NU_EBAR})) {
67          _h_q2_K ->fill(q2(p, PID::K0L));
68        }
69      }
70
71    }
72
73
74    /// Normalise histograms etc., after the run
75    void finalize() {
76      // normalize to unity
77      normalize(_h_q2_K );
78      normalize(_h_q2_pi);
79
80    }
81
82    /// @}
83
84
85    /// @name Histograms
86    /// @{
87    Histo1DPtr _h_q2_K,_h_q2_pi;
88    /// @}
89
90
91  };
92
93
94  RIVET_DECLARE_PLUGIN(BESIII_2017_I1519425);
95
96
97}