1// -*- C++ -*-
 2#include "Rivet/Analysis.hh"
 3#include "Rivet/Projections/UnstableParticles.hh"
 4
 5namespace Rivet {
 6
 7
 8  /// @brief B -> chi_c1 K*
 9  class BELLE_2006_I689881 : public Analysis {
10  public:
11
12    /// Constructor
13    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2006_I689881);
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      UnstableParticles ufs = UnstableParticles(Cuts::abspid==511);
23      declare(ufs, "UFS");
24      // histograms
25      book(_h,1,1,1);
26    }
27
28    bool isK(int pid) const {
29      return pid==130 || pid==310 || pid==311 || pid==321;
30    }
31
32    bool isPi(int pid) const {
33      return pid==211 || pid==111;
34    }
35
36    /// Perform the per-event analysis
37    void analyze(const Event& event) {
38      UnstableParticles ufs = apply<UnstableParticles>(event, "UFS");
39      for(const Particle & B : ufs.particles()) {
40        if (B.children().size()!=2) continue;
41        Particle chic,Kstar;
42        if (B.children()[0].pid()==20443 && B.children()[1].abspid()==313) {
43          chic = B.children()[0];
44          Kstar = B.children()[1];
45        }
46        else if (B.children()[1].pid()==20443 && B.children()[0].abspid()==313) {
47          chic = B.children()[1];
48          Kstar = B.children()[0];
49        }
50        else {
51          continue;
52        }
53        // find Kstar decay products
54        Particle K;
55        if (isK (Kstar.children()[0].abspid()) && isPi(Kstar.children()[1].abspid())) {
56          K = Kstar.children()[0];
57        }
58        else if (isK (Kstar.children()[1].abspid()) &&isPi(Kstar.children()[0].abspid())) {
59          K = Kstar.children()[1];
60        }
61        else {
62          continue;
63        }
64        // boost to B rest frame
65        LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(B.momentum().betaVec());
66        FourMomentum pChi   = boost.transform(chic.momentum());
67        FourMomentum pKstar = boost.transform(Kstar.momentum());
68        FourMomentum pK     = boost.transform(K    .momentum());
69        // axes
70        Vector3 axisX = pChi.p3().unit();
71        // kaon helicity angle
72        LorentzTransform boostK = LorentzTransform::mkFrameTransformFromBeta(pKstar.betaVec());
73        double cosK = -axisX.dot(boostK.transform(pK).p3().unit());
74        // fill hists
75        _h->fill(cosK);
76      }
77    }
78
79
80    /// Normalise histograms etc., after the run
81    void finalize() {
82      normalize(_h,1.,false);
83    }
84
85    /// @}
86
87
88    /// @name Histograms
89    /// @{
90    Histo1DPtr _h;
91    /// @}
92
93
94  };
95
96
97  RIVET_DECLARE_PLUGIN(BELLE_2006_I689881);
98
99}