Rivet analyses referenceCMS_2019_I1764472Measurement of the differential ttbar production cross section as a function of the jet mass and top quark mass in boosted hadronic top quark decays.Experiment: CMS (LHC) Inspire ID: 1764472 Status: VALIDATED Authors:
Beam energies: (6500.0, 6500.0) GeV Run details:
A measurement of the ttbar production cross section as a function of the jet mass of hadronic decays of boosted top quarks is presented. The measurement is carried out in the lepton+jets channel. As leptons, muons and electrons are defined with originate from the W boson decay. Jets are clustered from all stable particles excluding neutrinos in a two-step procedure using the XCone algorithm. At first, two large jets (R=1.2) are found aiming at a reconstruction of the two top quarks. Using the constituents of those jets, XCone is run again finding three subjets with R=0.4. A jet representing the hadronic and leptonic top quark decay is found by the angular distance to the leading lepton in the event. The final jets are constructed as the sum of the subjet four-momenta. The jet identified as the one containing the hadronic top quark decay is required to have \pt > 400 GeV. Furthermore, the jet mass of this jet has to be larger than the invariant mass of the combined system of second jet and lepton. Both, the differential and normalized differential ttbar production cross sections are measured as a function of the jet mass. Source code: CMS_2019_I1764472.cc 1// -*- C++ -*-
2#include "Rivet/Analysis.hh"
3#include "Rivet/Projections/PartonicTops.hh"
4#include "Rivet/Projections/FinalState.hh"
5#include "Rivet/Projections/VetoedFinalState.hh"
6#include "Rivet/Projections/PromptFinalState.hh"
7#include "Rivet/Projections/FastJets.hh"
8#include "Rivet/Projections/DressedLeptons.hh"
9#include "Rivet/Projections/ChargedLeptons.hh"
10
11#include "fastjet/contrib/Nsubjettiness.hh"
12#include "fastjet/contrib/XConePlugin.hh"
13
14namespace Rivet {
15
16
17 /// @brief Measurement of the jet mass for boosted top quarks at 13 TeV
18 class CMS_2019_I1764472 : public Analysis {
19 public:
20
21 /// Constructor
22 RIVET_DEFAULT_ANALYSIS_CTOR(CMS_2019_I1764472);
23
24
25 /// @name Analysis methods
26 //@{
27
28 void init() {
29
30 // Prompt leptons
31 ChargedLeptons charged_leptons;
32 PromptFinalState prompt_leptons(charged_leptons);
33 declare(prompt_leptons, "PromptLeptons");
34
35 // Final state particles for jet clustering
36 VetoedFinalState fs_jets;
37 fs_jets.vetoNeutrinos();
38
39 // First XCone jet clustering step
40 fastjet::contrib::PseudoXConePlugin* plugin_xcone = new fastjet::contrib::PseudoXConePlugin(2, 1.2, 2.0);
41 declare(FastJets(fs_jets, plugin_xcone), "FatJets");
42
43 // Partonic tops for decay channel definition
44 declare(PartonicTops(PartonicTops::DecayMode::E_MU, false), "LeptonicTops");
45 declare(PartonicTops(PartonicTops::DecayMode::HADRONIC), "HadronicTops");
46
47 // Book histograms
48 book(_hist_mass, "d01-x01-y01");
49 book(_hist_mass_norm, "d02-x01-y01");
50 }
51
52
53 /// Perform the per-event analysis
54 void analyze(const Event& event) {
55
56 // Decay mode check
57 const Particles& leptonicTops = apply<PartonicTops>(event, "LeptonicTops").particlesByPt();
58 const Particles& hadronicTops = apply<PartonicTops>(event, "HadronicTops").particlesByPt();
59 if (leptonicTops.size() != 1 || hadronicTops.size() != 1) vetoEvent;
60
61
62 // Get prompt leptons
63 const PromptFinalState& prompt_leptons = apply<PromptFinalState>(event, "PromptLeptons");
64 const Particles & leptons = prompt_leptons.particles();
65 if(leptons.empty()) vetoEvent;
66
67 // Select leading lepton
68 Particle lepton;
69 for(const Particle& l : leptons){
70 if(l.pT() > lepton.pT()) lepton = l;
71 }
72 if(lepton.pT() < 60*GeV) vetoEvent;
73
74 // Get the fat jets
75 const Jets& fatjets = applyProjection<FastJets>(event, "FatJets").jets();
76
77 // Get index of hadronic jet by distance to lepton
78 int ihad = 0;
79 int ilep = 1;
80
81 double dR0 = deltaR(lepton, fatjets.at(0));
82 double dR1 = deltaR(lepton, fatjets.at(1));
83
84 if(dR0 < dR1){
85 ihad = 1;
86 ilep = 0;
87 }
88
89 // Get jet constituents
90 const Particles & phad = fatjets.at(ihad).particles();
91 const Particles & plep = fatjets.at(ilep).particles();
92
93 // Cluster subjets
94 FinalState fs_dummy;
95 fastjet::JetDefinition::Plugin* plugin_subhad = new fastjet::contrib::PseudoXConePlugin(3, 0.4, 2.0);
96 fastjet::contrib::PseudoXConePlugin* plugin_sublep = new fastjet::contrib::PseudoXConePlugin(3, 0.4, 2.0);
97 FastJets hadsubcluster(fs_dummy, plugin_subhad);
98 FastJets lepsubcluster(fs_dummy, plugin_sublep);
99 hadsubcluster.calc(phad);
100 lepsubcluster.calc(plep);
101
102 Jets subjets_had = hadsubcluster.jets();
103 Jets subjets_lep = lepsubcluster.jets();
104
105 // Subtract the lepton four vector from closest subjet if dR<0.4
106 Jets subjets_had_clean;
107 double dRmin_had = 0.4;
108 unsigned int i_dRmin_had = 0;
109 bool found_match_had = false;
110 for(unsigned int i=0; i<subjets_had.size(); i++){
111 double dR = deltaR(subjets_had[i], lepton);
112 if(dR < dRmin_had){
113 dRmin_had = dR;
114 i_dRmin_had = i;
115 found_match_had = true;
116 }
117 }
118 for(unsigned int i=0; i<subjets_had.size(); i++){
119 Jet subjet = subjets_had[i];
120 if(found_match_had && i == i_dRmin_had) subjet = Jet(subjets_had[i].momentum()-lepton.momentum(), subjets_had[i].particles(), subjets_had[i].tags());
121 subjets_had_clean.push_back(subjet);
122 }
123 std::sort(subjets_had_clean.begin(), subjets_had_clean.end(), cmpMomByPt);
124
125 // do the same for lep jets
126 Jets subjets_lep_clean;
127 double dRmin_lep = 0.4;
128 unsigned int i_dRmin_lep = 0;
129 bool found_match_lep = false;
130 for(unsigned int i=0; i<subjets_lep.size(); i++){
131 double dR = deltaR(subjets_lep[i], lepton);
132 if(dR < dRmin_lep){
133 dRmin_lep = dR;
134 i_dRmin_lep = i;
135 found_match_lep = true;
136 }
137 }
138 for(unsigned int i=0; i<subjets_lep.size(); i++){
139 Jet subjet = subjets_lep[i];
140 if(found_match_lep && i == i_dRmin_lep) subjet = Jet(subjets_lep[i].momentum()-lepton.momentum(), subjets_lep[i].particles(), subjets_lep[i].tags());
141 subjets_lep_clean.push_back(subjet);
142 }
143 std::sort(subjets_lep_clean.begin(), subjets_lep_clean.end(), cmpMomByPt);
144
145 // Subjet cuts
146 if(subjets_had_clean.size() != 3) vetoEvent;
147 if(subjets_lep_clean.size() != 3) vetoEvent;
148 for (Jet jet : subjets_had_clean){
149 if(jet.pT() < 30*GeV) vetoEvent;
150 if(jet.abseta() > 2.5) vetoEvent;
151 }
152
153 // Combine subjets to final jets
154 FourMomentum hadjet;
155 for(Jet subjet : subjets_had_clean){
156 if(subjet.abseta() < 2.5) hadjet += subjet.momentum();
157 }
158 FourMomentum lepjet;
159 for(Jet subjet : subjets_lep_clean){
160 if(subjet.abseta() < 2.5) lepjet += subjet.momentum();
161 }
162
163 // Jet pT cuts
164 if(hadjet.pT() < 400*GeV) vetoEvent;
165 if(lepjet.pT() < 10*GeV) vetoEvent;
166
167 // m(hadjet) > m(lepjet+lepton)
168 FourMomentum secondJetLepton = lepjet + lepton.momentum();
169 if(hadjet.mass() < secondJetLepton.mass()) vetoEvent;
170
171 // Fill histograms
172 _hist_mass->fill(hadjet.mass()/GeV);
173 _hist_mass_norm->fill(hadjet.mass()/GeV);
174
175 }
176
177 /// Normalise and scale histograms
178 void finalize() {
179 const double sf = crossSection() / femtobarn / sumOfWeights();
180 scale(_hist_mass, sf);
181 normalize(_hist_mass_norm, 1.0, false);
182 }
183
184 //@}
185
186
187 private:
188
189 // Histograms
190 Histo1DPtr _hist_mass, _hist_mass_norm;
191
192 };
193
194
195
196 RIVET_DECLARE_PLUGIN(CMS_2019_I1764472);
197
198}
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