1// -*- C++ -*-
 2#include "Rivet/Analysis.hh"
 3#include "Rivet/Projections/UnstableParticles.hh"
 4
 5namespace Rivet {
 6
 7
 8  /// @brief B_s0 -> D_s* semileptonic decay
 9  class LHCB_2020_I1787090 : public Analysis {
10  public:
11
12    /// Constructor
13    RIVET_DEFAULT_ANALYSIS_CTOR(LHCB_2020_I1787090);
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_w , 1, 1, 1);
27    }
28
29    // Calculate the Q2 using mother and daugher meson
30    double w(const Particle& B, int mesonID) {
31      Particle D = select(B.children(), Cuts::pid==mesonID)[0];
32      FourMomentum q = B.mom() -D.mom() ;
33      double q2 = q*q;
34      return 0.5*(sqr(B.mass())+sqr(D.mass())-q2)/B.mass()/D.mass();
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      for (const Particle& p :  apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid==531)) {
49	if(p.pid()<0) {
50	  if(isSemileptonicDecay(p, {433, PID::MUON, PID::NU_MUBAR})) {
51	    _h_w->fill(w(p, 433));
52	  }
53	}
54	else {
55	  if(isSemileptonicDecay(p, {-433, PID::ANTIMUON, PID::NU_MU})) {
56	    _h_w->fill(w(p, -433));
57	  }
58	}
59      }
60    }
61
62
63    /// Normalise histograms etc., after the run
64    void finalize() {
65      // normalize to unity
66      normalize(_h_w);
67    }
68
69    /// @}
70
71
72    /// @name Histograms
73    /// @{
74    Histo1DPtr _h_w;
75    /// @}
76
77
78  };
79
80
81  RIVET_DECLARE_PLUGIN(LHCB_2020_I1787090);
82
83}