1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
| // -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/IdentifiedFinalState.hh"
#include "Rivet/Projections/PromptFinalState.hh"
#include "Rivet/Projections/DressedLeptons.hh"
namespace Rivet {
/// Inclusive 4-lepton lineshape
class ATLAS_2015_I1394865 : public Analysis {
public:
/// Default constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2015_I1394865);
void init() {
FinalState fs(Cuts::abseta < 5.0);
PromptFinalState pfs(Cuts::abseta < 5.0);
IdentifiedFinalState photon(fs, PID::PHOTON);
IdentifiedFinalState bare_EL(pfs, {PID::ELECTRON, -PID::ELECTRON});
IdentifiedFinalState bare_MU(pfs, {PID::MUON, -PID::MUON});
// Selection 1: ZZ-> llll selection
Cut etaranges_el = Cuts::abseta < 2.5 && Cuts::pT > 7*GeV;
Cut etaranges_mu = Cuts::abseta < 2.7 && Cuts::pT > 6*GeV;
DressedLeptons electron_sel4l(photon, bare_EL, 0.1, etaranges_el);
declare(electron_sel4l, "ELECTRON_sel4l");
DressedLeptons muon_sel4l(photon, bare_MU, 0.1, etaranges_mu);
declare(muon_sel4l, "MUON_sel4l");
// Both ZZ on-shell histos
book(_h_ZZ_mZZ , 1, 1, 1);
book(_h_ZZ_pTZZ, 2, 1, 1);
}
/// Do the analysis
void analyze(const Event& e) {
////////////////////////////////////////////////////////////////////
// Preselection of leptons for ZZ-> llll final state
////////////////////////////////////////////////////////////////////
Particles leptons_sel4l;
const vector<DressedLepton>& mu_sel4l = apply<DressedLeptons>(e, "MUON_sel4l").dressedLeptons();
const vector<DressedLepton>& el_sel4l = apply<DressedLeptons>(e, "ELECTRON_sel4l").dressedLeptons();
const vector<DressedLepton> leptonsFS_sel4l = mu_sel4l + el_sel4l;
// leptonsFS_sel4l.insert( leptonsFS_sel4l.end(), mu_sel4l.begin(), mu_sel4l.end() );
// leptonsFS_sel4l.insert( leptonsFS_sel4l.end(), el_sel4l.begin(), el_sel4l.end() );
// mu: pT > 6 GeV, eta < 2.7; ele: pT > 7 GeV, eta < 2.5
for (const DressedLepton& l : leptonsFS_sel4l) {
if (l.abspid() == PID::ELECTRON) leptons_sel4l.push_back(l); // REDUNDANT: if (l.pT() > 7*GeV && l.abseta() < 2.5)
else if (l.abspid() == PID::MUON) leptons_sel4l.push_back(l); // REDUNDANT: if (l.pT() > 6*GeV && l.abseta() < 2.7)
}
//////////////////////////////////////////////////////////////////
// Exactly two opposite charged leptons
//////////////////////////////////////////////////////////////////
// Calculate total 'flavour' charge
double totalcharge = 0;
for (const Particle& l : leptons_sel4l) totalcharge += l.pid();
// Analyze 4 lepton events
if (leptons_sel4l.size() != 4 || totalcharge != 0) vetoEvent;
// Identify Z states from 4 lepton pairs
Zstate Z1, Z2, Z1_alt, Z2_alt;
if ( !identifyZstates(Z1, Z2, Z1_alt, Z2_alt, leptons_sel4l) ) vetoEvent;
const double mZ1 = Z1.mom().mass();
const double mZ2 = Z2.mom().mass();
const double mZ1_alt = Z1_alt.mom().mass();
const double mZ2_alt = Z2_alt.mom().mass();
const double pTZ1 = Z1.mom().pT();
const double pTZ2 = Z2.mom().pT();
const double mZZ = (Z1.mom() + Z2.mom()).mass();
const double pTZZ = (Z1.mom() + Z2.mom()).pT();
// Event selections
// pT(Z) > 2 GeV
bool pass = pTZ1 > 2*GeV && pTZ2 > 2*GeV;
if (!pass) vetoEvent;
// Lepton kinematics: pT > 20, 15, 10 (8 if muon) GeV
int n1 = 0, n2 = 0, n3 = 0;
for (Particle& l : leptons_sel4l) {
if (l.pT() > 20*GeV) ++n1;
if (l.pT() > 15*GeV) ++n2;
if (l.pT() > 10*GeV && l.abspid() == PID::ELECTRON) ++n3;
if (l.pT() > 8*GeV && l.abspid() == PID::MUON) ++n3;
}
pass = pass && n1>=1 && n2>=2 && n3>=3;
if (!pass) vetoEvent;
// Dilepton mass: 50 < mZ1 < 120 GeV, 12 < mZ2 < 120 GeV
pass = pass && mZ1 > 50*GeV && mZ1 < 120*GeV;
pass = pass && mZ2 > 12*GeV && mZ2 < 120*GeV;
if (!pass) vetoEvent;
// Lepton separation: deltaR(l, l') > 0.1 (0.2) for same- (different-) flavor leptons
for (size_t i = 0; i < leptons_sel4l.size(); ++i) {
for (size_t j = i + 1; j < leptons_sel4l.size(); ++j) {
const Particle& l1 = leptons_sel4l[i];
const Particle& l2 = leptons_sel4l[j];
pass = pass && deltaR(l1, l2) > (l1.abspid() == l2.abspid() ? 0.1 : 0.2);
if (!pass) vetoEvent;
}
}
// J/Psi veto: m(l+l-) > 5 GeV
pass = pass && mZ1 > 5*GeV && mZ2 > 5*GeV && mZ1_alt > 5*GeV && mZ2_alt > 5*GeV;
if (!pass) vetoEvent;
// 80 < m4l < 1000 GeV
pass = pass && mZZ > 80*GeV && mZZ < 1000*GeV;
if (!pass) vetoEvent;
// Fill histograms
_h_ZZ_mZZ->fill(mZZ);
_h_ZZ_pTZZ->fill(pTZZ);
}
/// Finalize
void finalize() {
const double norm = crossSection()/sumOfWeights()/femtobarn*TeV;
scale(_h_ZZ_mZZ, norm);
scale(_h_ZZ_pTZZ, norm);
}
/// Generic Z candidate
struct Zstate : public ParticlePair {
Zstate() { }
Zstate(ParticlePair _particlepair) : ParticlePair(_particlepair) { }
FourMomentum mom() const { return first.momentum() + second.momentum(); }
operator FourMomentum() const { return mom(); }
static bool cmppT(const Zstate& lx, const Zstate& rx) { return lx.mom().pT() < rx.mom().pT(); }
};
/// @brief 4l to ZZ assignment algorithm
///
/// ZZ->4l pairing
/// - At least two same flavour opposite sign (SFOS) lepton pairs
/// - Ambiguities in pairing are resolved following the procedure
/// 1. the leading Z (Z1) is choosen as the SFOS with dilepton mass closet to Z mass
/// 2. the subleading Z (Z2) is choosen as the remaining SFOS dilepton pair
///
/// Z1, Z2: the selected pairing
/// Z1_alt, Z2_alt: the alternative pairing (the same as Z1, Z2 in 2e2m case)
bool identifyZstates(Zstate& Z1, Zstate& Z2, Zstate& Z1_alt, Zstate& Z2_alt, const Particles& leptons_sel4l) {
const double ZMASS = 91.1876*GeV;
bool findZZ = false;
Particles part_pos_el, part_neg_el, part_pos_mu, part_neg_mu;
for (const Particle& l : leptons_sel4l) {
if (l.abspid() == PID::ELECTRON) {
if (l.pid() < 0) part_neg_el.push_back(l);
if (l.pid() > 0) part_pos_el.push_back(l);
}
else if (l.abspid() == PID::MUON) {
if (l.pid() < 0) part_neg_mu.push_back(l);
if (l.pid() > 0) part_pos_mu.push_back(l);
}
}
// eeee/mmmm channel
if ((part_neg_el.size() == 2 && part_pos_el.size() == 2) || (part_neg_mu.size() == 2 && part_pos_mu.size() == 2)) {
findZZ = true;
Zstate Zcand_1, Zcand_2, Zcand_3, Zcand_4;
Zstate Zcand_1_tmp, Zcand_2_tmp, Zcand_3_tmp, Zcand_4_tmp;
if (part_neg_el.size() == 2) { // eeee
Zcand_1_tmp = Zstate( ParticlePair( part_neg_el[0], part_pos_el[0] ) );
Zcand_2_tmp = Zstate( ParticlePair( part_neg_el[0], part_pos_el[1] ) );
Zcand_3_tmp = Zstate( ParticlePair( part_neg_el[1], part_pos_el[0] ) );
Zcand_4_tmp = Zstate( ParticlePair( part_neg_el[1], part_pos_el[1] ) );
}
else { // mmmm
Zcand_1_tmp = Zstate( ParticlePair( part_neg_mu[0], part_pos_mu[0] ) );
Zcand_2_tmp = Zstate( ParticlePair( part_neg_mu[0], part_pos_mu[1] ) );
Zcand_3_tmp = Zstate( ParticlePair( part_neg_mu[1], part_pos_mu[0] ) );
Zcand_4_tmp = Zstate( ParticlePair( part_neg_mu[1], part_pos_mu[1] ) );
}
// We can have the following pairs: (Z1 + Z4) || (Z2 + Z3)
// Firstly, reorder withing each quadruplet to have
// - fabs(mZ1 - ZMASS) < fabs(mZ4 - ZMASS)
// - fabs(mZ2 - ZMASS) < fabs(mZ3 - ZMASS)
if (fabs(Zcand_1_tmp.mom().mass() - ZMASS) < fabs(Zcand_4_tmp.mom().mass() - ZMASS)) {
Zcand_1 = Zcand_1_tmp;
Zcand_4 = Zcand_4_tmp;
} else {
Zcand_1 = Zcand_4_tmp;
Zcand_4 = Zcand_1_tmp;
}
if (fabs(Zcand_2_tmp.mom().mass() - ZMASS) < fabs(Zcand_3_tmp.mom().mass() - ZMASS)) {
Zcand_2 = Zcand_2_tmp;
Zcand_3 = Zcand_3_tmp;
} else {
Zcand_2 = Zcand_3_tmp;
Zcand_3 = Zcand_2_tmp;
}
// We can have the following pairs: (Z1 + Z4) || (Z2 + Z3)
// Secondly, select the leading and subleading Z following
// 1. the leading Z (Z1) is choosen as the SFOS with dilepton mass closet to Z mass
// 2. the subleading Z (Z2) is choosen as the remaining SFOS dilepton pair
if (fabs(Zcand_1.mom().mass() - ZMASS) < fabs(Zcand_2.mom().mass() - ZMASS)) {
Z1 = Zcand_1;
Z2 = Zcand_4;
Z1_alt = Zcand_2;
Z2_alt = Zcand_3;
} else {
Z1 = Zcand_2;
Z2 = Zcand_3;
Z1_alt = Zcand_1;
Z2_alt = Zcand_4;
}
} // end of eeee/mmmm channel
else if (part_neg_el.size() == 1 && part_pos_el.size() == 1 && part_neg_mu.size() == 1 && part_pos_mu.size() == 1) { // 2e2m channel
findZZ = true;
Zstate Zcand_1, Zcand_2;
Zcand_1 = Zstate( ParticlePair( part_neg_mu[0], part_pos_mu[0] ) );
Zcand_2 = Zstate( ParticlePair( part_neg_el[0], part_pos_el[0] ) );
if (fabs(Zcand_1.mom().mass() - ZMASS) < fabs(Zcand_2.mom().mass() - ZMASS)) {
Z1 = Zcand_1;
Z2 = Zcand_2;
} else {
Z1 = Zcand_2;
Z2 = Zcand_1;
}
Z1_alt = Z1;
Z2_alt = Z2;
}
return findZZ;
}
private:
Histo1DPtr _h_ZZ_pTZZ, _h_ZZ_mZZ;
};
// The hook for the plugin system
RIVET_DECLARE_PLUGIN(ATLAS_2015_I1394865);
}
|