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## Rivet analyses reference

### ATLAS_2016_I1468168

Dileptonic $e \mu$ $t\bar{t}$ early cross-section measurement at 13 TeV
Experiment: ATLAS (LHC)
Inspire ID: 1468168
Status: VALIDATED
Authors:
• Tom Neep
• Barbara Alvarez Gonzalez
• Yang Qin
References:
Beams: p+ p+
Beam energies: (6500.0, 6500.0) GeV
Run details:
• $t\bar{t}$ production

This paper describes a measurement of the inclusive top quark pair production cross-section ($\sigma_{t\bar{t}}$) with a data sample of 3.2 fb${}^{-1}$ of proton-proton collisions at a centre-of-mass energy of $\sqrt{s}=13$ TeV, collected in 2015 by the ATLAS detector at the LHC. This measurement uses events with an opposite-charge electron-muon pair in the final state. Jets containing $b$-quarks are tagged using an algorithm based on track impact parameters and reconstructed secondary vertices. The numbers of events with exactly one and exactly two $b$-tagged jets are counted and used to determine simultaneously $\sigma_{t\bar{t}}$ and the efficiency to reconstruct and $b$-tag a jet from a top quark decay, thereby minimising the associated systematic uncertainties. The cross-section is measured to be: $\sigma_{t\bar{t}} = 818 \pm 8$ (stat) $\pm 27$ (syst) $\pm 19$ (lumi) $\pm 12$ (beam) pb, where the four uncertainties arise from data statistics, experimental and theoretical systematic effects, the integrated luminosity and the LHC beam energy, giving a total relative uncertainty of 4.4\%. The result is consistent with theoretical QCD calculations at next-to-next-to-leading order. A fiducial measurement corresponding to the experimental acceptance of the leptons is also presented.

Source code: ATLAS_2016_I1468168.cc
  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 #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 { class ATLAS_2016_I1468168 : public Analysis { public: DEFAULT_RIVET_ANALYSIS_CTOR(ATLAS_2016_I1468168); void init() { // Eta ranges Cut eta_full = Cuts::abseta < 5.0 && Cuts::pT >= 1.0*MeV; // Lepton cuts Cut lep_cuts = Cuts::abseta < 2.5 && Cuts::pT >= 25.0*GeV; // All final state particles FinalState fs(eta_full); // Get photons to dress leptons IdentifiedFinalState photons(fs); photons.acceptIdPair(PID::PHOTON); // Projection to find the electrons IdentifiedFinalState el_id(fs); el_id.acceptIdPair(PID::ELECTRON); PromptFinalState electrons(el_id); electrons.acceptTauDecays(true); DressedLeptons dressedelectrons(photons, electrons, 0.1, lep_cuts, true); declare(dressedelectrons, "DressedElectrons"); // Projection to find the muons IdentifiedFinalState mu_id(fs); mu_id.acceptIdPair(PID::MUON); PromptFinalState muons(mu_id); muons.acceptTauDecays(true); DressedLeptons dressedmuons(photons, muons, 0.1, lep_cuts, true); declare(dressedmuons, "DressedMuons"); book(_s , 2, 1 ,1); book(_c , "_counter"); } void analyze(const Event& event) { // Get the selected objects, using the projections. const size_t num_es = apply(event, "DressedElectrons").dressedLeptons().size(); const size_t num_mus = apply(event, "DressedMuons").dressedLeptons().size(); // Evaluate basic event selection const bool pass_emu = num_es == 1 && num_mus == 1; if (!pass_emu) vetoEvent; // Fill histogram to measure the event acceptance _c->fill(); } void finalize() { // Normalize to cross-section scale(_c, crossSection() / sumOfWeights()); double err = _c->err(); _s->addPoint(13*TeV, _c->val(), make_pair(0.5, 0.5), make_pair(err,err)); } private: CounterPtr _c; Scatter2DPtr _s; }; // The hook for the plugin system DECLARE_RIVET_PLUGIN(ATLAS_2016_I1468168); }