Rivet analyses referenceBELLE_2011_I916712$X(3872)$ mass and angular distributions using $B\to KX(3872)$Experiment: BELLE (KEKB) Inspire ID: 916712 Status: VALIDATED NOHEPDATA Authors:
Beam energies: ANY Run details:
Measurement of mass and angular distribution for the production of $X(3872)$ in the decay $B\to KX(3872)$. There is no consensus as to the nature of the $X(3872)$ $c\bar{c}$ state and therefore we taken its PDG code to be 9030443, i.e. the first unused code for an undetermined spin one $c\bar{c}$ state. This can be changed using the PID option if a different code is used by the event generator performing the simulation. Source code: BELLE_2011_I916712.cc 1// -*- C++ -*-
2#include "Rivet/Analysis.hh"
3#include "Rivet/Projections/UnstableParticles.hh"
4
5namespace Rivet {
6
7
8 /// @brief B -> K X(3872)
9 class BELLE_2011_I916712 : public Analysis {
10 public:
11
12 /// Constructor
13 RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2011_I916712);
14
15
16 /// @name Analysis methods
17 /// @{
18
19 /// Book histograms and initialise projections before the run
20 void init() {
21 // set the PDG code
22 _pid = getOption<double>("PID", 9030443);
23 // projections
24 declare(UnstableParticles(Cuts::abspid==511 ||
25 Cuts::abspid==521), "UFS");
26 // histograms
27 for(unsigned int ix=0;ix<4;++ix)
28 book(_h[ix],1+ix,1,1);
29 }
30
31 void findChildren(const Particle & p, Particles & pim, Particles & pip,
32 Particles & Jpsi, unsigned int &ncount) {
33 for( const Particle &child : p.children()) {
34 if(child.pid()==PID::PIPLUS) {
35 pip.push_back(child);
36 ncount+=1;
37 }
38 else if(child.pid()==PID::PIMINUS) {
39 pim.push_back(child);
40 ncount+=1;
41 }
42 else if(child.pid()==PID::JPSI) {
43 Jpsi.push_back(child);
44 ncount+=1;
45 }
46 else if(child.children().empty()) {
47 ncount+=1;
48 }
49 else
50 findChildren(child,pim,pip,Jpsi,ncount);
51 }
52 }
53
54 /// Perform the per-event analysis
55 void analyze(const Event& event) {
56 for(const Particle & p : apply<UnstableParticles>(event, "UFS").particles()) {
57 if(p.children().empty()) continue;
58 if(p.children().size()==1) continue;
59 if(p.children().size()!=2) continue;
60 Particle K,X;
61 if(p.children()[0].pid()==_pid) {
62 X = p.children()[0];
63 K = p.children()[1];
64 }
65 else if(p.children()[1].pid()==_pid) {
66 X = p.children()[1];
67 K = p.children()[0];
68 }
69 else continue;
70 if(K.abspid()!=311 && K.abspid()!=321 &&
71 K.abspid()!=310 && K.abspid()!=130) continue;
72 // X(3872) decay
73 unsigned int ncount=0;
74 Particles pip,pim,Jpsi;
75 findChildren(X,pim,pip,Jpsi,ncount);
76 if( ncount!=3 || !(pim.size()==1 && pip.size()==1 && Jpsi.size()==1)) continue;
77 _h[3]->fill((pip[0].momentum()+pim[0].momentum()).mass());
78 LorentzTransform boostB = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
79 Vector3 axisX = -boostB.transform(K.momentum()).p3().unit();
80 FourMomentum pX = boostB.transform(X .momentum());
81 LorentzTransform boostX = LorentzTransform::mkFrameTransformFromBeta(pX.betaVec());
82 FourMomentum pPsi = boostX.transform(boostB.transform(Jpsi[0].momentum()));
83 double cTheta = axisX.dot(pPsi.p3().unit());
84 _h[0]->fill(cTheta);
85 // finally the leptons from J/psi decay
86 if(Jpsi[0].children().size()!=2) vetoEvent;
87 if(Jpsi[0].children()[0].pid()!=-Jpsi[0].children()[1].pid()) vetoEvent;
88 if(Jpsi[0].children()[0].abspid()!=PID::EMINUS &&
89 Jpsi[0].children()[0].abspid()!=PID::MUON) vetoEvent;
90 Particle lm = Jpsi[0].children()[0];
91 Particle lp = Jpsi[0].children()[1];
92 Vector3 axispi = boostX.transform(boostB(pip[0].momentum())).p3().unit();
93 Vector3 axisZ = axispi.cross(axisX).unit();
94 Vector3 axisL = boostX.transform(boostB(lp.momentum())).p3().unit();
95 _h[2]->fill(abs(axisZ.dot(axisL)));
96 _h[1]->fill(abs(axisX.dot(axisL)));
97 }
98 }
99
100
101 /// Normalise histograms etc., after the run
102 void finalize() {
103 for(unsigned int ix=0;ix<4;++ix)
104 normalize(_h[ix],1.,false);
105 }
106
107 /// @}
108
109
110 /// @name Histograms
111 /// @{
112 Histo1DPtr _h[4];
113 int _pid;
114 /// @}
115
116
117 };
118
119
120 RIVET_DECLARE_PLUGIN(BELLE_2011_I916712);
121
122}
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