Rivet analyses referenceATLAS_2021_I1913061b-fragmentation at 13 TeVExperiment: ATLAS (LHC) Inspire ID: 1913061 Status: VALIDATED Authors:
Beam energies: (6500.0, 6500.0) GeV Run details:
The fragmentation properties of jets containing $b$-hadrons are studied using charged $B$-mesons in 139 fb$^{-1}$ of $pp$ collisions at $\sqrt{s} = 13$ TeV, recorded with the ATLAS detector at the LHC during the period from 2015 to 2018. The $B$ mesons are reconstructed using the decay of $B^{\pm}$ into $J/\psi K^{\pm}$, with the $J/\psi$ decaying into a pair of muons. Jets are reconstructed using the anti-$k_t$ algorithm with radius parameter $R=0.4$. The measurement determines the longitudinal and transverse momentum profiles of the reconstructed $B$-hadrons with respect to the axes of the jets to which they are geometrically associated. These distributions are measured in intervals of the jet transverse momentum, ranging from 50 GeV to above 100 GeV. The results are corrected for detector effects and compared with several Monte Carlo predictions using different parton shower and hadronisation models. The results for the longitudinal and transverse profiles provide useful inputs to improve the description of heavy-flavour fragmentation in jets. Source code: ATLAS_2021_I1913061.cc 1// -*- C++ -*-
2#include "Rivet/Analysis.hh"
3#include "Rivet/Projections/FinalState.hh"
4#include "Rivet/Projections/PromptFinalState.hh"
5#include "Rivet/Projections/LeptonFinder.hh"
6#include "Rivet/Projections/VetoedFinalState.hh"
7#include "Rivet/Projections/UnstableParticles.hh"
8#include "Rivet/Projections/FastJets.hh"
9
10namespace Rivet {
11
12
13 /// @brief b-fragmentation at 13 TeV
14 class ATLAS_2021_I1913061 : public Analysis {
15
16 public:
17
18 /// Default constructor
19 RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2021_I1913061);
20
21 /// @name Analysis methods
22 /// @{
23
24 void init() {
25
26 //Jet building: anti-kT R = 0.4, including muons and neutrinos.
27 FinalState photons(Cuts::abspid == PID::PHOTON);
28
29 PromptFinalState bare_mu(Cuts::abspid == PID::MUON, TauDecaysAs::PROMPT);
30 LeptonFinder all_dressed_mu(bare_mu, photons, 0.1, Cuts::abseta < 2.5);
31
32 PromptFinalState bare_el(Cuts::abspid == PID::ELECTRON, TauDecaysAs::PROMPT);
33 LeptonFinder all_dressed_el(bare_el, photons, 0.1, Cuts::abseta < 2.5);
34
35 VetoedFinalState vfs(FinalState(Cuts::abseta < 4.5));
36 vfs.addVetoOnThisFinalState(all_dressed_el);
37 vfs.addVetoOnThisFinalState(all_dressed_mu);
38
39 FastJets jets(vfs, JetAlg::ANTIKT, 0.4, JetMuons::ALL, JetInvisibles::DECAY);
40 declare(jets, "JETS");
41
42 //Charged B mesons
43 UnstableParticles bpm_fs(Cuts::abspid == 521);
44 declare(bpm_fs, "BPM_FS");
45
46 // Book histograms
47 book(_h["zFrag_pt01"], 1,1,1);
48 book(_h["ptRel_pt01"], 2,1,1);
49 book(_h["zFrag_pt02"], 3,1,1);
50 book(_h["ptRel_pt02"], 4,1,1);
51 book(_h["zFrag_pt03"], 5,1,1);
52 book(_h["ptRel_pt03"], 6,1,1);
53 book(_p["zFrag"], 7,1,1);
54 book(_p["ptRel"], 8,1,1);
55 }
56
57
58 /// Perform the per-event analysis
59 void analyze(const Event& event) {
60
61 const Jets& jets = apply<FastJets>(event, "JETS").jetsByPt(Cuts::pT > 7*GeV);
62 const Particles& bpmFS = apply<UnstableParticles>(event, "BPM_FS").particlesByPt();
63
64 //Preselect B mesons in J/psi K decay channel
65 Particles goodHadrons;
66
67 for (const Particle& p : bpmFS) {
68
69 bool passKaon = 0;
70 bool passMuon1 = 0;
71 bool passMuon2 = 0;
72
73 const Particles& bDecays = p.children();
74
75 for (const Particle& s : bDecays){
76
77 if (s.abspid() == PID::KPLUS && s.pt() > 4*GeV) passKaon = 1;
78 if (s.abspid() == PID::JPSI) {
79
80 const Particles& jpsiDecays = s.children();
81
82 for (const Particle& m : jpsiDecays){
83
84 if (m.pid() == PID::ANTIMUON && m.pt() > 6*GeV) passMuon1 = 1;
85 if (m.pid() == PID::MUON && m.pt() > 6*GeV) passMuon2 = 1;
86 }
87 }
88 }
89
90 if (passKaon && passMuon1 && passMuon2) goodHadrons += p;
91 }
92
93 //Preselect jets passing kinematic cuts
94 Jets goodJets;
95 for (size_t i = 0; i < jets.size(); ++i) {
96 if (jets[i].pT() <= 20*GeV) continue;
97 if (jets[i].abseta() >= 2.1) continue;
98 bool overlaps = false;
99 for (size_t j = i + 1; j < jets.size(); ++j) {
100 if (jets[j].pT() > 20*GeV && deltaR(jets[i], jets[j]) < 0.8) {
101 overlaps = true; break;
102 }
103 }
104 if (!overlaps) goodJets += jets[i];
105 }
106
107 //Associate the jets to the B hadrons.
108 for (const Jet& thisJet : goodJets) {
109
110 Particles jetHads;
111 for (const Particle& thisHad : goodHadrons) {
112 if (deltaR(thisJet, thisHad) < 0.4) jetHads += thisHad;
113 }
114
115 if (jetHads.size() == 1){
116 const Particle& jetHadron = jetHads[0];
117
118 //Out-of-cone correction for B-decay products
119 Vector3 jetVector = momentum3(thisJet); Vector3 jetVector0 = jetVector;
120 Vector3 hadronVector = momentum3(jetHadron);
121 Vector3 kaonVector; Vector3 muonVector1; Vector3 muonVector2;
122
123 const Particles& bDecays = jetHadron.children();
124 for (const Particle& s : bDecays){
125
126 if (s.abspid() == PID::KPLUS) kaonVector = momentum3(s);
127 if (s.abspid() == PID::JPSI) {
128
129 const Particles& jpsiDecays = s.children();
130
131 for (const Particle& m : jpsiDecays){
132
133 if (m.pid() == PID::ANTIMUON && m.pt() > 6*GeV) muonVector1 = momentum3(m);
134 if (m.pid() == PID::MUON && m.pt() > 6*GeV) muonVector2 = momentum3(m);
135 }
136 }
137 }
138
139 if (deltaR(muonVector1, jetVector0) > 0.4) jetVector += muonVector1;
140 if (deltaR(muonVector2, jetVector0) > 0.4) jetVector += muonVector2;
141 if (deltaR(kaonVector, jetVector0) > 0.4) jetVector += kaonVector;
142
143 if (jetVector.perp() <= 30.0*GeV) vetoEvent;
144 if (jetVector.abseta() >= 2.1) vetoEvent;
145 if (deltaR(jetVector, hadronVector) >= 0.4) vetoEvent;
146
147 //Longitudinal and transverse profiles
148 double zFrag = hadronVector.dot(jetVector)/jetVector.mod2();
149 double ptRel = (hadronVector.cross(jetVector)).mod()/jetVector.mod();
150
151 if (jetVector.perp() >= 50*GeV && jetVector.perp() < 70*GeV) {
152 if (zFrag <= 0.23) zFrag = 0.24;
153 if (zFrag >= 1.00) zFrag = 0.99;
154 if (ptRel >= 8.00) ptRel = 7.90;
155
156 _h["zFrag_pt01"]->fill(zFrag);
157 _h["ptRel_pt01"]->fill(ptRel);
158 }
159
160 if (jetVector.perp() >= 70*GeV && jetVector.perp() < 100*GeV) {
161 if (zFrag <= 0.23) zFrag = 0.24;
162 if (zFrag >= 1.00) zFrag = 0.99;
163 if (ptRel >= 10.0) ptRel = 9.90;
164
165 _h["zFrag_pt02"]->fill(zFrag);
166 _h["ptRel_pt02"]->fill(ptRel);
167 }
168
169 if (jetVector.perp() >= 100*GeV) {
170 if (zFrag <= 0.16) zFrag = 0.17;
171 if (zFrag >= 1.00) zFrag = 0.99;
172 if (ptRel >= 14.0) ptRel = 13.9;
173
174 _h["zFrag_pt03"]->fill(zFrag);
175 _h["ptRel_pt03"]->fill(ptRel);
176 }
177
178 double ptFill = jetVector.perp()/GeV;
179 if (ptFill >= 150.) ptFill = 125.;
180
181 // For pTrel, we need to weight the mean by 1/binWidth
182 // (what is being plotted is the mean of the histogram, not the variable!)
183 // This doesn't apply to z since all bins have the same width.
184 double binWidth = 0.0;
185 double transBins[12] = { 0.0, 0.5, 1.0, 1.5, 2.2, 3.0, 4.0, 5.0, 6.5, 8.0, 10.0, 14.0 };
186
187 for (size_t iBin = 0; iBin < 11; ++iBin) {
188 if (ptRel >= transBins[iBin] && ptRel < transBins[iBin+1]) binWidth = transBins[iBin+1]-transBins[iBin];
189 }
190
191 _p["zFrag"]->fill(ptFill, zFrag);
192 _p["ptRel"]->fill(ptFill, ptRel, 1./binWidth);
193
194 }
195 }
196 }
197
198
199 void finalize() {
200 normalize(_h);
201 }
202
203
204 private:
205
206 //Histograms
207 map<string, Histo1DPtr> _h;
208 map<string, Profile1DPtr> _p;
209
210 };
211
212
213 RIVET_DECLARE_PLUGIN(ATLAS_2021_I1913061);
214
215}
|
