Rivet analyses referenceATLAS_2019_I1720442Inclusive 4-lepton lineshape at 13 TeVExperiment: ATLAS (LHC) Inspire ID: 1720442 Status: VALIDATED Authors:
Beam energies: (6500.0, 6500.0) GeV Run details:
A measurement of the four-lepton invariant mass spectrum is made with the ATLAS detector, using an integrated luminosity of 36.1 fb$^{-1}$ of proton-proton collisions at $\sqrt{s} = 13$ TeV delivered by the Large Hadron Collider. The differential cross-section is measured for events containing two same-flavour opposite-sign lepton pairs. It exhibits a rich structure, with different mass regions dominated in the Standard Model by single $Z$ boson production, Higgs boson production, and $Z$ boson pair production, and non-negligible interference effects at high invariant masses. The measurement is compared with state-of-the-art Standard Model calculations, which are found to be consistent with the data. These calculations are used to interpret the data in terms of $gg\to ZZ\to 4\ell$ and $Z\to 4\ell$ subprocesses, and to place constraints on a possible contribution from physics beyond the Standard Model. Source code: ATLAS_2019_I1720442.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
7namespace Rivet {
8
9
10 /// ATLAS 4-lepton lineshape at 13 TeV
11 class ATLAS_2019_I1720442 : public Analysis {
12 public:
13
14 /// Constructor
15 RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2019_I1720442);
16
17 void init() {
18
19 PromptFinalState photons(Cuts::abspid == PID::PHOTON);
20 PromptFinalState elecs(Cuts::abspid == PID::ELECTRON);
21 PromptFinalState muons(Cuts::abspid == PID::MUON);
22
23 // Selection
24 Cut el_fid_sel = (Cuts::abseta < 2.47) && (Cuts::pT > 7*GeV);
25 Cut mu_fid_sel = (Cuts::abseta < 2.7) && (Cuts::pT > 5*GeV);
26
27 LeptonFinder dressed_elecs(elecs, photons, 0.005, el_fid_sel);
28 declare(dressed_elecs, "elecs");
29
30 LeptonFinder dressed_muons(muons, photons, 0.005, mu_fid_sel);
31 declare(dressed_muons, "muons");
32
33 // Book histos
34 book(_h["m4l_inclusive"], 1,1,1);
35
36 book(_h["m4l_ptslice1"], 2,1,1);
37 book(_h["m4l_ptslice2"], 3,1,1);
38 book(_h["m4l_ptslice3"], 4,1,1);
39 book(_h["m4l_ptslice4"], 5,1,1);
40
41 book(_h["m4l_rapidityslice1"], 6,1,1);
42 book(_h["m4l_rapidityslice2"], 7,1,1);
43 book(_h["m4l_rapidityslice3"], 8,1,1);
44 book(_h["m4l_rapidityslice4"], 9,1,1);
45
46 book(_h["m4l_4mu"], 12,1,1);
47 book(_h["m4l_4e"], 13,1,1);
48 book(_h["m4l_2e2mu"], 14,1,1);
49 }
50
51
52 /// @brief Generic dilepton candidate
53 /// @todo Move into the Rivet core?
54 struct Dilepton : public ParticlePair {
55 Dilepton() { }
56 Dilepton(ParticlePair _particlepair) : ParticlePair(_particlepair) {
57 assert(first.abspid() == second.abspid());
58 }
59 FourMomentum mom() const { return first.momentum() + second.momentum(); }
60 operator FourMomentum() const { return mom(); }
61 static bool cmppT(const Dilepton& lx, const Dilepton& rx) { return lx.mom().pT() < rx.mom().pT(); }
62 int flavour() const { return first.abspid(); }
63 double pTl1() const { return first.pT(); }
64 double pTl2() const { return second.pT(); }
65 };
66
67
68 struct Quadruplet {
69 Quadruplet (Dilepton z1, Dilepton z2): _z1(z1), _z2(z2) { }
70 enum class FlavCombi { mm=0, ee, me, em, undefined };
71 FourMomentum mom() const { return _z1.mom() + _z2.mom(); }
72 Dilepton getZ1() const { return _z1; }
73 Dilepton getZ2() const { return _z2; }
74 Dilepton _z1, _z2;
75 FlavCombi type() const {
76 if ( _z1.flavour() == 13 && _z2.flavour() == 13) { return FlavCombi::mm; }
77 else if (_z1.flavour() == 11 && _z2.flavour() == 11) { return FlavCombi::ee; }
78 else if (_z1.flavour() == 13 && _z2.flavour() == 11) { return FlavCombi::me; }
79 else if (_z1.flavour() == 11 && _z2.flavour() == 13) { return FlavCombi::em; }
80 else return FlavCombi::undefined;
81 }
82 };
83
84
85 vector<Quadruplet> getBestQuads(Particles& particles) {
86 // H->ZZ->4l pairing
87 // - Two same flavor opposite charged leptons
88 // - Ambiguities in pairing are resolved by choosing the combination
89 // that results in the smaller value of |mll - mZ| for each pair successively
90 vector<Quadruplet> quads {};
91
92 size_t n_parts = particles.size();
93 if (n_parts < 4) return quads;
94
95 // STEP 1: find SFOS pairs
96 vector<Dilepton> SFOS;
97 for (size_t i = 0; i < n_parts; ++i) {
98 for (size_t j = 0; j < i; ++j) {
99 if (particles[i].pid() == -particles[j].pid()) {
100 // sort such that the negative lepton is listed first
101 if (particles[i].pid() > 0) SFOS.push_back(Dilepton(make_pair(particles[i], particles[j])));
102 else SFOS.push_back(Dilepton(make_pair(particles[j], particles[i])));
103 }
104 }
105 }
106 if (SFOS.size() < 2) return quads;
107
108 // now we sort the SFOS pairs
109 std::sort(SFOS.begin(), SFOS.end(), [](const Dilepton& p1, const Dilepton& p2) {
110 return fabs(p1.mom().mass() - Z_mass) < fabs(p2.mom().mass() - Z_mass);
111 });
112
113 // Form all possible quadruplets passing the pT cuts
114 for (size_t k = 0; k < SFOS.size(); ++k) {
115 for (size_t l = k+1; l < SFOS.size(); ++l) {
116 if (deltaR(SFOS[k].first.mom(), SFOS[l].first.mom()) < 1e-13) continue;
117 if (deltaR(SFOS[k].first.mom(), SFOS[l].second.mom()) < 1e-13) continue;
118 if (deltaR(SFOS[k].second.mom(), SFOS[l].first.mom()) < 1e-13) continue;
119 if (deltaR(SFOS[k].second.mom(), SFOS[l].second.mom()) < 1e-13) continue;
120
121 vector<double> lep_pt { SFOS[k].pTl1(), SFOS[k].pTl2(), SFOS[l].pTl1(), SFOS[l].pTl2() };
122 std::sort(lep_pt.begin(), lep_pt.end(), std::greater<double>());
123 if (!(lep_pt[0] > 20*GeV && lep_pt[1] > 15*GeV && lep_pt[2] > 10*GeV)) continue;
124 quads.push_back( Quadruplet(SFOS[k], SFOS[l]) );
125 }
126 }
127 return quads;
128 }
129
130
131 bool passMassCuts(const Quadruplet& theQuad){
132 const vector<double> cuts_m34{ 5*GeV, 5*GeV, 12*GeV, 12*GeV, 50*GeV };
133 const vector<double> cuts_m4l{ 0, 100*GeV, 110*GeV, 140*GeV, 190*GeV };
134
135 double m4l = theQuad.mom().mass();
136 double mZ1 = theQuad.getZ1().mom().mass();
137 double mZ2 = theQuad.getZ2().mom().mass();
138
139 // Invariant-mass requirements
140 double cutval = cuts_m34.back();
141 for (size_t k = 0; k < cuts_m34.size(); ++k) {
142 if (cuts_m4l[k] > m4l) {
143 cutval = cuts_m34[k-1] + (cuts_m34[k] - cuts_m34[k-1])/(cuts_m4l[k] - cuts_m4l[k-1]) * (m4l - cuts_m4l[k-1]);
144 break;
145 }
146 }
147 return inRange(mZ1, 50*GeV, 106*GeV) && inRange(mZ2, cutval, 115*GeV);
148 }
149
150
151 bool pass_dRll(const Quadruplet& theQuad) {
152 const double dR_min_same = 0.1;
153 const double dR_min_opp = 0.2;
154 double dr_min_cross = dR_min_opp;
155 if (theQuad.getZ1().flavour() == theQuad.getZ2().flavour()) {
156 dr_min_cross = dR_min_same;
157 }
158 return !((deltaR(theQuad.getZ1().first, theQuad.getZ1().second) < dR_min_same) ||
159 (deltaR(theQuad.getZ2().first, theQuad.getZ2().second) < dR_min_same) ||
160 (deltaR(theQuad.getZ1().first, theQuad.getZ2().first) < dr_min_cross) ||
161 (deltaR(theQuad.getZ1().first, theQuad.getZ2().second) < dr_min_cross) ||
162 (deltaR(theQuad.getZ1().second, theQuad.getZ2().first) < dr_min_cross) ||
163 (deltaR(theQuad.getZ1().second, theQuad.getZ2().second) < dr_min_cross));
164 }
165
166
167 bool pass_Jpsi(const Quadruplet& theQuad){
168 Particles all_leps { theQuad.getZ1().first, theQuad.getZ1().second, theQuad.getZ2().first, theQuad.getZ2().second };
169 for (const Particle& lep1 : all_leps) {
170 for (const Particle& lep2 : all_leps) {
171 if (lep1.pid() == -lep2.pid() && (lep1.mom() + lep2.mom()).mass() < 5*GeV) return false;
172 }
173 }
174 return true;
175 }
176
177
178 // Handle 3 further CF stages - m12/34, dRmin, jpsi veto
179 bool passSelection (const Quadruplet& theQuad){
180 return passMassCuts(theQuad) && pass_dRll(theQuad) && pass_Jpsi(theQuad);
181 }
182
183
184 // Do the analysis
185 void analyze(const Event& event) {
186
187 //preselection of leptons for ZZ-> llll final state
188 Particles dressed_leptons;
189 for (auto lep : apply<LeptonFinder>(event, "muons").dressedLeptons()) { dressed_leptons.push_back(lep); }
190 for (auto lep : apply<LeptonFinder>(event, "elecs").dressedLeptons()) { dressed_leptons.push_back(lep); }
191
192 auto foundDressed = getBestQuads(dressed_leptons);
193 // if we don't find any quad, we can stop here
194 if (foundDressed.empty()) vetoEvent;
195
196 bool pass = passSelection(foundDressed[0]);
197 if (pass) {
198 double m4l = foundDressed[0].mom().mass()/GeV;
199 double pt4l = foundDressed[0].mom().pT()/GeV;
200 double y4l = foundDressed[0].mom().absrap();
201 Quadruplet::FlavCombi flavour = foundDressed[0].type();
202 _h["m4l_inclusive"]->fill(m4l);
203 if ( pt4l < 20.) _h["m4l_ptslice1"]->fill(m4l);
204 else if (pt4l < 50.) _h["m4l_ptslice2"]->fill(m4l);
205 else if (pt4l < 100.) _h["m4l_ptslice3"]->fill(m4l);
206 else if (pt4l < 600.) _h["m4l_ptslice4"]->fill(m4l);
207
208 if ( y4l < 0.4) _h["m4l_rapidityslice1"]->fill(m4l);
209 else if (y4l < 0.8) _h["m4l_rapidityslice2"]->fill(m4l);
210 else if (y4l < 1.2) _h["m4l_rapidityslice3"]->fill(m4l);
211 else if (y4l < 2.5) _h["m4l_rapidityslice4"]->fill(m4l);
212
213 if ( flavour == Quadruplet::FlavCombi::mm) _h["m4l_4mu"]->fill(m4l);
214 else if (flavour == Quadruplet::FlavCombi::ee) _h["m4l_4e"]->fill(m4l);
215 else if (flavour == Quadruplet::FlavCombi::me || flavour == Quadruplet::FlavCombi::em) {
216 _h["m4l_2e2mu"]->fill(m4l);
217 }
218 }
219
220 }
221
222
223 /// Finalize
224 void finalize() {
225 const double sf = crossSection() / femtobarn / sumOfWeights();
226 scale(_h, sf);
227 }
228
229
230 private:
231
232 map<string, Histo1DPtr> _h;
233 static constexpr double Z_mass = 91.1876;
234
235 };
236
237
238 RIVET_DECLARE_PLUGIN(ATLAS_2019_I1720442);
239
240}
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