Rivet analyses referenceBABAR_2009_I827985Helicity angle distributions in excited $D_s$ meson decaysExperiment: BABAR (PEP-II) Inspire ID: 827985 Status: VALIDATED Authors:
Beam energies: ANY Run details:
The decays $D_s^{**} \to D^{*+}K^0_S\to D^0\pi^+K^0_S$ are used to measure the helicity angle, i.e. the angle between the pion and kaon in the rest frame of the $D^*$. The decays of $D_{s1}^*(2700)^+$ and with mass 2.8 GeV were measured. It is unclear if this is the $D_{s1}^*(2860)^+$, $D_{s3}^*(2860)^+$ or a mixture of the two. This histogram is therefore filled we with each state and the admixture. The data were read from the plots in the papers. Source code: BABAR_2009_I827985.cc 1// -*- C++ -*-
2#include "Rivet/Analysis.hh"
3#include "Rivet/Projections/UnstableParticles.hh"
4
5namespace Rivet {
6
7
8 /// @brief D**_s decays
9 class BABAR_2009_I827985 : public Analysis {
10 public:
11
12 /// Constructor
13 RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2009_I827985);
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_DStar_ctheta, 1,1,1);
27 book(_h_D3_ctheta[0], 1,1,2);
28 book(_h_D3_ctheta[1], 1,1,3);
29 book(_h_D3_ctheta[2], 1,1,4);
30 }
31
32 /// Recursively walk the decay tree to find decay products of @a p
33 void findDecayProducts(Particle mother, Particles & dstar, Particles & d0, Particles & K0, Particles & pi, unsigned int & ncount) {
34 for(const Particle & p: mother.children()) {
35 if(p.abspid()==413)
36 dstar.push_back(p);
37 else if(p.abspid()==421)
38 d0.push_back(p);
39 else if(p.abspid()==130 || p.abspid()==130 || p.abspid()==311)
40 K0.push_back(p);
41 else if(p.abspid()==211)
42 pi.push_back(p);
43 ncount +=1;
44 }
45 }
46
47 /// Perform the per-event analysis
48 void analyze(const Event& event) {
49 for(const Particle& p : apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid==100433 || Cuts::abspid==437 ||
50 Cuts::abspid==30433)) {
51 // decay products
52 Particles dstar,d0,K0,pi;
53 unsigned int ncount=0;
54 findDecayProducts(p, dstar, d0, K0, pi, ncount);
55 if(ncount!=2 || dstar.size()!=1 || K0.size()!=1 ) continue;
56 if(dstar[0].pid()/p.pid()<0) continue;
57 Particle p2 = dstar[0];
58 LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(p2.momentum().betaVec());
59 Vector3 d1 = boost.transform(K0[0].momentum()).p3().unit();
60 ncount=0;
61 dstar.clear();
62 d0.clear();
63 pi.clear();
64 findDecayProducts(p2, dstar, d0, K0, pi, ncount);
65 if(ncount!=2 || pi.size()!=1 || d0.size()!=1 ) continue;
66 if(pi[0].pid()/p2.pid()<0) continue;
67 Vector3 d2 = boost.transform(pi[0].momentum()).p3().unit();
68 double cTheta = d1.dot(d2);
69 // decay angles
70 if(p.abspid()==100433)
71 _h_DStar_ctheta->fill(cTheta);
72 else if(p.abspid()==30433) {
73 _h_D3_ctheta[0]->fill(cTheta);
74 _h_D3_ctheta[2]->fill(cTheta);
75 }
76 else if(p.abspid()==437) {
77 _h_D3_ctheta[1]->fill(cTheta);
78 _h_D3_ctheta[2]->fill(cTheta);
79 }
80 }
81 }
82
83
84 /// Normalise histograms etc., after the run
85 void finalize() {
86 normalize(_h_DStar_ctheta);
87 normalize(_h_D3_ctheta[0]);
88 normalize(_h_D3_ctheta[1]);
89 normalize(_h_D3_ctheta[2]);
90 }
91
92 /// @}
93
94
95 /// @name Histograms
96 /// @{
97 Histo1DPtr _h_DStar_ctheta,_h_D3_ctheta[3];
98 /// @}
99
100
101 };
102
103
104 RIVET_DECLARE_PLUGIN(BABAR_2009_I827985);
105
106}
|