Abstract
A search is presented for four-top-quark production using an integrated luminosity of 139 fb^{-1} of proton–proton collision data at a centre-of-mass energy of 13~text {TeV} collected by the ATLAS detector at the LHC. Events are selected if they contain a same-sign lepton pair or at least three leptons (electrons or muons). Jet multiplicity, jet flavour and event kinematics are used to separate signal from the background through a multivariate discriminant, and dedicated control regions are used to constrain the dominant backgrounds. The four-top-quark production cross section is measured to be 24^{+7}_{-6} fb. This corresponds to an observed (expected) significance with respect to the background-only hypothesis of 4.3 (2.4) standard deviations and provides evidence for this process.
Highlights
The ATLAS detectorThe ATLAS experiment [16,17,18] at the LHC is a multipurpose particle detector with a forward–backward symmetric cylindrical geometry and a nearly 4π coverage in solid angle. It consists of an inner tracking detector (ID) surrounded by a thin superconducting solenoid providing a 2T axial magnetic field, electromagnetic (EM) and hadron calorimeters, and a muon spectrometer
Background estimationBackgrounds in the 2LSS/3L channel can be categorised as irreducible and reducible
In the analysis described in this paper, signal events are separated from background events using a multivariate discriminant
Summary
The ATLAS experiment [16,17,18] at the LHC is a multipurpose particle detector with a forward–backward symmetric cylindrical geometry and a nearly 4π coverage in solid angle. It consists of an inner tracking detector (ID) surrounded by a thin superconducting solenoid providing a 2T axial magnetic field, electromagnetic (EM) and hadron calorimeters, and a muon spectrometer. The ATLAS experiment [16,17,18] at the LHC is a multipurpose particle detector with a forward–backward symmetric cylindrical geometry and a nearly 4π coverage in solid angle.. The ATLAS experiment [16,17,18] at the LHC is a multipurpose particle detector with a forward–backward symmetric cylindrical geometry and a nearly 4π coverage in solid angle.2 It consists of an inner tracking detector (ID) surrounded by a thin superconducting solenoid providing a 2T axial magnetic field, electromagnetic (EM) and hadron calorimeters, and a muon spectrometer. The inner tracking detector covers the pseudorapidity range |η| < 2.5. It consists of silicon pixel, silicon microstrip, and transition radiation tracking detectors. This is followed by a software-based trigger that reduces the accepted event rate to 1kHz, on average, depending on the data-taking conditions [19]
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