scholarly journals Evidence for $$t\bar{t}t\bar{t}$$ production in the multilepton final state in proton–proton collisions at $$\sqrt{s}=13$$ $$\text {TeV}$$ with the ATLAS detector

2020 ◽  
Vol 80 (11) ◽  
Author(s):  
G. Aad ◽  
◽  
B. Abbott ◽  
D. C. Abbott ◽  
A. Abed Abud ◽  
...  
Keyword(s):  
Top Quark ◽  
Production Cross ◽  
Atlas Detector ◽  
Proton Collision ◽  
Final State ◽  
Proton Proton ◽  
Top Quark Production ◽  
Quark Production ◽  
Proton Proton Collision ◽  
Multivariate Discriminant

AbstractA search is presented for four-top-quark production using an integrated luminosity of 139 fb$$^{-1}$$ - 1 of proton–proton collision data at a centre-of-mass energy of $$13~\text {TeV}$$ 13 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 $$24^{+7}_{-6}$$ 24 - 6 + 7  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.

scholarly journals Measurement of single top-quark production in association with a W boson in the single-lepton channel at $$\sqrt{s} = 8\,\text {TeV}$$ with the ATLAS detector

2021 ◽  
Vol 81 (8) ◽  
Author(s):  
G. Aad ◽  
B. Abbott ◽  
D. C. Abbott ◽  
A. Abed Abud ◽  
K. Abeling ◽  
...  
Keyword(s):  
Neural Network ◽  
Cross Section ◽  
Top Quark ◽  
W Boson ◽  
Production Cross ◽  
Hadron Collider ◽  
Atlas Detector ◽  
Proton Proton ◽  
Top Quark Production ◽  
Quark Production

AbstractThe production cross-section of a top quark in association with a W boson is measured using proton–proton collisions at $$\sqrt{s} = 8\,\text {TeV}$$ s = 8 TeV . The dataset corresponds to an integrated luminosity of $$20.2\,\text {fb}^{-1}$$ 20.2 fb - 1 , and was collected in 2012 by the ATLAS detector at the Large Hadron Collider at CERN. The analysis is performed in the single-lepton channel. Events are selected by requiring one isolated lepton (electron or muon) and at least three jets. A neural network is trained to separate the tW signal from the dominant $$t{\bar{t}}$$ t t ¯ background. The cross-section is extracted from a binned profile maximum-likelihood fit to a two-dimensional discriminant built from the neural-network output and the invariant mass of the hadronically decaying W boson. The measured cross-section is $$\sigma _{tW} = 26 \pm 7\,\text {pb}$$ σ tW = 26 ± 7 pb , in good agreement with the Standard Model expectation.

scholarly journals Measurement of the t$$ \overline{t} $$t$$ \overline{t} $$ production cross section in pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector

2021 ◽  
Vol 2021 (11) ◽  
Author(s):  
◽  
G. Aad ◽  
B. Abbott ◽  
D. C. Abbott ◽  
A. Abed Abud ◽  
...  
Keyword(s):  
Cross Section ◽  
Top Quark ◽  
Production Cross Section ◽  
Production Cross ◽  
Atlas Detector ◽  
Proton Collision ◽  
Atlas Collaboration ◽  
Top Quark Production ◽  
Quark Production ◽  
Standard Deviations

Abstract A measurement of four-top-quark production using proton-proton collision data at a centre-of-mass energy of 13 TeV collected by the ATLAS detector at the Large Hadron Collider corresponding to an integrated luminosity of 139 fb−1 is presented. Events are selected if they contain a single lepton (electron or muon) or an opposite-sign lepton pair, in association with multiple jets. The events are categorised according to the number of jets and how likely these are to contain b-hadrons. A multivariate technique is then used to discriminate between signal and background events. The measured four-top-quark production cross section is found to be $$ {26}_{-15}^{+17} $$ 26 − 15 + 17 fb, with a corresponding observed (expected) significance of 1.9 (1.0) standard deviations over the background-only hypothesis. The result is combined with the previous measurement performed by the ATLAS Collaboration in the multilepton final state. The combined four-top-quark production cross section is measured to be $$ {24}_{-6}^{+7} $$ 24 − 6 + 7 fb, with a corresponding observed (expected) signal significance of 4.7 (2.6) standard deviations over the background-only predictions. It is consistent within 2.0 standard deviations with the Standard Model expectation of 12.0 ± 2.4 fb.

scholarly journals Search for s-channel single top-quark production in proton–proton collisions at s=8 TeV with the ATLAS detector

2015 ◽  
Vol 740 ◽  
pp. 118-136 ◽  
Author(s):  
G. Aad ◽  
B. Abbott ◽  
J. Abdallah ◽  
S. Abdel Khalek ◽  
O. Abdinov ◽  
...  
Keyword(s):  
Top Quark ◽  
Atlas Detector ◽  
Proton Proton ◽  
Proton Collisions ◽  
Single Top ◽  
Top Quark Production ◽  
Quark Production ◽  
8 Tev ◽  
Proton Proton Collisions

scholarly journals Search for type-III seesaw heavy leptons in dilepton final states in pp collisions at $$ \sqrt{s} = 13\,{\text {TeV}} $$ with the ATLAS detector

2021 ◽  
Vol 81 (3) ◽  
Author(s):  
G. Aad ◽  
◽  
B. Abbott ◽  
D. C. Abbott ◽  
A. Abed Abud ◽  
...  
Keyword(s):  
Hadron Collider ◽  
Atlas Detector ◽  
Proton Collision ◽  
Final State ◽  
Proton Proton ◽  
Type Iii ◽  
Missing Transverse Momentum ◽  
Proton Proton Collision ◽  
Heavy Leptons ◽  
Two Jets

AbstractA search for the pair production of heavy leptons as predicted by the type-III seesaw mechanism is presented. The search uses proton–proton collision data at a centre-of-mass energy of 13 TeV, corresponding to $$ 139\,{\text {fb}}^{-1} $$ 139 fb - 1 of integrated luminosity recorded by the ATLAS detector during Run 2 of the Large Hadron Collider. The analysis focuses on the final state with two light leptons (electrons or muons) of different flavour and charge combinations, with at least two jets and large missing transverse momentum. No significant excess over the Standard Model expectation is observed. The results are translated into exclusion limits on heavy-lepton masses, and the observed lower limit on the mass of the type-III seesaw heavy leptons is 790 GeV at 95% confidence level.

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