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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:
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
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86 | #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 {
/// @brief dileptonic e-mu ttbar
class ATLAS_2016_I1468168 : public Analysis {
public:
RIVET_DEFAULT_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<DressedLeptons>(event, "DressedElectrons").dressedLeptons().size();
const size_t num_mus = apply<DressedLeptons>(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
RIVET_DECLARE_PLUGIN(ATLAS_2016_I1468168);
}
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