Rivet analyses referenceCMS_2018_I1686000Fiducial single-top + photon cross-section measurement at 13 TeVExperiment: CMS (LHC) Inspire ID: 1682495 Status: VALIDATED Authors:
Beam energies: (6500.0, 6500.0) GeV Run details:
The first evidence of events consistent with the production of a single top quark in association with a photon is reported. The analysis is based on proton-proton collisions at s=13 TeV and recorded by the CMS experiment in 2016, corresponding to an integrated luminosity of 35.9 fb-1. Events are selected by requiring the presence of a muon, a photon, an imbalance in transverse momentum from an undetected neutrino, and at least two jets of which exactly one is identified as associated with the hadronization of a b quark. A multivariate discriminant based on topological and kinematic event properties is employed to separate signal from background processes. An excess above the background-only hypothesis is observed, with a significance of 4.4 standard deviations. A fiducial cross section is measured for isolated photons with transverse momentum greater than 25 GeV in the central region of the detector. The measured product of the cross section and branching fraction is $115 \pm 17 \text{ (stat)} \pm 30 \text{ (syst)} \mathrm{fb}$, consistent with the Standard Model prediction. Warning: the fiducial definition in this analysis relies on generation-level cuts and cannot be exactly reproduced. Source code: CMS_2018_I1686000.cc 1// -*- C++ -*-
2#include "Rivet/Analysis.hh"
3#include "Rivet/Projections/LeptonFinder.hh"
4#include "Rivet/Projections/FastJets.hh"
5#include "Rivet/Projections/MergedFinalState.hh"
6#include "Rivet/Projections/IdentifiedFinalState.hh"
7#include "Rivet/Projections/MissingMomentum.hh"
8#include "Rivet/Projections/PartonicTops.hh"
9#include "Rivet/Projections/PromptFinalState.hh"
10
11namespace Rivet {
12
13
14 /// Fiducial single-top + photon cross-section measurement at 13 TeV
15 class CMS_2018_I1686000 : public Analysis {
16 public:
17
18 /// Constructor
19 RIVET_DEFAULT_ANALYSIS_CTOR(CMS_2018_I1686000);
20
21
22 /// @name Analysis methods
23 /// @{
24
25 /// Book histograms and initialise projections before the run
26 void init() {
27
28 // Leptons
29 declare(LeptonFinder(Cuts::abseta < 2.4 && Cuts::pT > 26*GeV, 0.1), "Leptons");
30
31 // Jets
32 declare(FastJets(FinalState(Cuts::abseta < 5), JetAlg::ANTIKT, 0.4), "Jets");
33
34 // Photons
35 declare(PromptFinalState(Cuts::pid == PID::PHOTON && Cuts::pT > 25*GeV && Cuts::abseta < 1.44), "Photons");
36
37 // MET
38 declare(MissingMomentum(FinalState(Cuts::abseta < 5)), "MET");
39
40
41 // Book xsec counter
42 book(_c_xsec_fid, "xsec");
43 }
44
45
46 /// Perform the per-event analysis
47 void analyze(const Event& event) {
48
49 // // Find at least 2 jets, one b-tagged
50 // const Jets jets = apply<JetFinder>(event, "Jets").jetsByPt(Cuts::abseta < 4.7 && Cuts::pT > 40*GeV);
51 // Jets bjets, ljets;
52 // for (const Jet& j : jets)
53 // ((j.abseta() < 2.5 && j.bTagged()) ? bjets : ljets) += j;
54 // if (bjets.empty() || ljets.empty()) vetoEvent;
55 // const Jet& bjet = bjets[0];
56 // const Jet& ljet = ljets[0];
57
58 // // Require exactly one isolated lepton, and it has to be a muon
59 // const Particles& leps = apply<FinalState>(event, "Leptons").particlesByPt();
60 // const Particles isoleps = discardIfAnyDeltaRLess(leps, jets, 0.3);
61 // if (isoleps.size() != 1 || isoleps[0].abspid() != PID::MUON) vetoEvent;
62 // const Particle& muon = isoleps[0];
63
64 // // Require exactly one isolated photon
65 // const Particles& photons = apply<FinalState>(event, "Photons").particlesByPt();
66 // const Particles muisophotons = discard(photons, deltaRLess(muon,0.5));
67 // const Particles isophotons = discardIfAnyDeltaRLess(muisophotons, Jets{bjet,ljet}, 0.5);
68 // if (isophotons.size() != 1) vetoEvent;
69
70 // // Require 30 GeV of missing ET
71 // const double met = apply<MissingMomentum>(event, "MET").met();
72 // if (met < 30*GeV) vetoEvent;
73
74
75 // Find light jets
76 const Jets jets = apply<JetFinder>(event, "Jets").jetsByPt();
77 const Jets ljets = discard(jets, [](const Jet& j){ return j.abseta() < 2.5 && j.bTagged(); } );
78
79 // Require a photon, isolated from the light jet
80 Particles photons = apply<FinalState>(event, "Photons").particlesByPt();
81 if (!ljets.empty()) idiscard(photons, deltaRLess(ljets[0], 0.5));
82 if (photons.empty()) vetoEvent;
83
84 // Fill counter
85 _c_xsec_fid->fill();
86 }
87
88
89 /// Normalise histograms etc., after the run
90 void finalize() {
91 const double BRmu = 0.13 + 0.13*0.17; //< decay BR direct to a muon, and to a muon via a tau
92 scale(_c_xsec_fid, BRmu*crossSection()/femtobarn/sumOfWeights());
93 }
94
95 /// @}
96
97
98 /// Counter
99 CounterPtr _c_xsec_fid;
100
101
102 };
103
104
105 RIVET_DECLARE_PLUGIN(CMS_2018_I1686000);
106
107}
|