Rivet analyses referenceBELLE_2012_I1123656Helicity angles in B0→D∗+D∗−Experiment: BELLE (KEKB) Inspire ID: 1123656 Status: VALIDATED NOHEPDATA Authors:
Beam energies: ANY Run details:
Helicity angle distributions in B0→D∗+D∗− decays Source code: BELLE_2012_I1123656.cc 1// -*- C++ -*-
2#include "Rivet/Analysis.hh"
3#include "Rivet/Projections/UnstableParticles.hh"
4
5namespace Rivet {
6
7
8 /// @brief B0 -> D*+ D*-
9 class BELLE_2012_I1123656 : public Analysis {
10 public:
11
12 /// Constructor
13 RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2012_I1123656);
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 for(unsigned int ix=0;ix<2;++ix)
26 book(_h[ix],1,1,1+ix);
27 }
28
29
30 /// Perform the per-event analysis
31 void analyze(const Event& event) {
32 Particles B0 = apply<UnstableParticles>(event, "UFS").particles();
33 for(const Particle & p : B0) {
34 if(p.children().size()!=2) continue;
35 if(p.children()[0].pid()!=-p.children()[1].pid()) continue;
36 if(p.children()[0].abspid()!=413) continue;
37 Particle Dp = p.children()[0];
38 Particle Dm = p.children()[1];
39 if (p.pid()>0 && Dp.pid()<0) swap(Dp,Dm);
40 else if(p.pid()<0 && Dp.pid()>0) swap(Dp,Dm);
41 // find children of the D mesons
42 Particle pip,pim;
43 if(Dp.children().size()!=2) continue;
44 if(Dp.children()[0].abspid()==PID::PIPLUS &&
45 Dp.children()[1].abspid()==PID::D0)
46 pip = Dp.children()[0];
47 else if (Dp.children()[1].abspid()==PID::PIPLUS &&
48 Dp.children()[0].abspid()==PID::D0)
49 pip = Dp.children()[1];
50 else
51 continue;
52 if(Dm.children().size()!=2) continue;
53 if(Dm.children()[0].abspid()==PID::PIPLUS &&
54 Dm.children()[1].abspid()==PID::D0) {
55 pim = Dm.children()[0];
56 }
57 else if (Dm.children()[1].abspid()==PID::PIPLUS &&
58 Dm.children()[0].abspid()==PID::D0) {
59 pim = Dm.children()[1];
60 }
61 else
62 continue;
63 // boost to rest frame
64 LorentzTransform boostB = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
65 FourMomentum pDstarPlus = boostB.transform(Dp.momentum());
66 FourMomentum pDstarMinus = boostB.transform(Dm.momentum());
67 LorentzTransform boostDp = LorentzTransform::mkFrameTransformFromBeta(pDstarPlus .betaVec());
68 FourMomentum ppip = boostDp.transform(boostB.transform(pip.momentum()));
69 LorentzTransform boostDm = LorentzTransform::mkFrameTransformFromBeta(pDstarMinus.betaVec());
70 FourMomentum ppim = boostDm.transform(boostB.transform(pim.momentum()));
71 Vector3 axisX = pDstarPlus.p3().unit();
72 // ctheta1
73 _h[1]->fill(axisX.dot(ppim.p3().unit()));
74 // y and z axis
75 ppim = boostDp.transform(boostB.transform(pim.momentum()));
76 Vector3 axisZ = axisX.cross(ppim.p3()).unit();
77 // cThetaTr
78 _h[0]->fill(axisZ.dot(ppip.p3().unit()));
79 }
80 }
81
82
83 /// Normalise histograms etc., after the run
84 void finalize() {
85 for(unsigned int ix=0;ix<2;++ix)
86 normalize(_h[ix],1.,false);
87 }
88
89 /// @}
90
91
92 /// @name Histograms
93 /// @{
94 Histo1DPtr _h[2];
95 /// @}
96
97
98 };
99
100
101 RIVET_DECLARE_PLUGIN(BELLE_2012_I1123656);
102
103}
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