scholarly journals Search for supersymmetry in final states with two same-sign or three leptons and jets using 36 fb−1 of $$ \sqrt{s}=13 $$ TeV pp collision data with the ATLAS detector

2017 ◽  
Vol 2017 (9) ◽  
Author(s):  
M. Aaboud ◽  
◽  
G. Aad ◽  
B. Abbott ◽  
O. Abdinov ◽  
...  
Keyword(s):  
Top Quark ◽  
Confidence Level ◽  
Standard Model Prediction ◽  
Hadron Collider ◽  
Atlas Detector ◽  
Proton Proton ◽  
Missing Transverse Momentum ◽  
Parity Conservation ◽  
Signal Region ◽  
Quark Models

Abstract A search for strongly produced supersymmetric particles using signatures involving multiple energetic jets and either two isolated same-sign leptons (e or μ), or at least three isolated leptons, is presented. The analysis relies on the identification of b-jets and high missing transverse momentum to achieve good sensitivity. A data sample of proton-proton collisions at $$ \sqrt{s}=13 $$ s = 13 TeV recorded with the ATLAS detector at the Large Hadron Collider in 2015 and 2016, corresponding to a total integrated luminosity of 36.1 fb−1, is used for the search. No significant excess over the Standard Model prediction is observed. The results are interpreted in several simplified supersymmetric models featuring R-parity conservation or R-parity violation, extending the exclusion limits from previous searches. In models considering gluino pair production, gluino masses are excluded up to 1.87 TeV at 95% confidence level. When bottom squarks are pair-produced and decay to a chargino and a top quark, models with bottom squark masses below 700 GeV and light neutralinos are excluded at 95% confidence level. In addition, model-independent limits are set on a possible contribution of new phenomena to the signal region yields.

scholarly journals Search for squarks and gluinos in final states with jets and missing transverse momentum using 139 fb−1 of $$ \sqrt{s} $$ = 13 TeV pp collision data with the ATLAS detector

2021 ◽  
Vol 2021 (2) ◽  
Author(s):  
G. Aad ◽  
◽  
B. Abbott ◽  
D. C. Abbott ◽  
A. Abed Abud ◽  
...  
Keyword(s):  
Transverse Momentum ◽  
Hadron Collider ◽  
Atlas Detector ◽  
Simplified Model ◽  
Supersymmetric Particle ◽  
Final States ◽  
Proton Proton ◽  
Missing Transverse Momentum ◽  
First And Second Generation ◽  
Proton Proton Collisions

Abstract A search for the supersymmetric partners of quarks and gluons (squarks and gluinos) in final states containing jets and missing transverse momentum, but no electrons or muons, is presented. The data used in this search were recorded by the ATLAS experiment in proton-proton collisions at a centre-of-mass energy of $$ \sqrt{s} $$ s = 13 TeV during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb−1. The results are interpreted in the context of various R-parity-conserving models where squarks and gluinos are produced in pairs or in association and a neutralino is the lightest supersymmetric particle. An exclusion limit at the 95% confidence level on the mass of the gluino is set at 2.30 TeV for a simplified model containing only a gluino and the lightest neutralino, assuming the latter is massless. For a simplified model involving the strong production of mass-degenerate first- and second-generation squarks, squark masses below 1.85 TeV are excluded if the lightest neutralino is massless. These limits extend substantially beyond the region of supersymmetric parameter space excluded previously by similar searches with the ATLAS detector.

scholarly journals Search for new phenomena in events with two opposite-charge leptons, jets and missing transverse momentum in pp collisions at $$ \sqrt{\mathrm{s}} $$ = 13 TeV with the ATLAS detector

2021 ◽  
Vol 2021 (4) ◽  
Author(s):  
G. Aad ◽  
◽  
B. Abbott ◽  
D. C. Abbott ◽  
A. Abed Abud ◽  
...  
Keyword(s):  
Dark Matter ◽  
Transverse Momentum ◽  
Pair Production ◽  
Hadron Collider ◽  
Atlas Detector ◽  
Top Squark ◽  
Proton Proton ◽  
Opposite Charge ◽  
Missing Transverse Momentum ◽  
Wide Range

Abstract The results of a search for direct pair production of top squarks and for dark matter in events with two opposite-charge leptons (electrons or muons), jets and missing transverse momentum are reported, using 139 fb−1 of integrated luminosity from proton-proton collisions at $$ \sqrt{s} $$ s = 13 TeV, collected by the ATLAS detector at the Large Hadron Collider during Run 2 (2015–2018). This search considers the pair production of top squarks and is sensitive across a wide range of mass differences between the top squark and the lightest neutralino. Additionally, spin-0 mediator dark-matter models are considered, in which the mediator is produced in association with a pair of top quarks. The mediator subsequently decays to a pair of dark-matter particles. No significant excess of events is observed above the Standard Model background, and limits are set at 95% confidence level. The results exclude top squark masses up to about 1 TeV, and masses of the lightest neutralino up to about 500 GeV. Limits on dark-matter production are set for scalar (pseudoscalar) mediator masses up to about 250 (300) GeV.

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.

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 Search for pair production of scalar leptoquarks decaying into first- or second-generation leptons and top quarks in proton–proton collisions at $$\sqrt{s}$$ = 13 TeV with the ATLAS detector

2021 ◽  
Vol 81 (4) ◽  
Author(s):  
G. Aad ◽  
◽  
B. Abbott ◽  
D. C. Abbott ◽  
A. Abed Abud ◽  
...  
Keyword(s):  
Pair Production ◽  
Top Quark ◽  
Hadron Collider ◽  
Atlas Detector ◽  
Large Radius ◽  
Proton Proton ◽  
Proton Collisions ◽  
Muon Channel ◽  
Scalar Leptoquarks ◽  
Proton Proton Collisions

AbstractA search for pair production of scalar leptoquarks, each decaying into either an electron or a muon and a top quark, is presented. This is the first leptoquark search using ATLAS data to investigate top-philic cross-generational couplings that could provide explanations for recently observed anomalies in B meson decays. This analysis targets high leptoquark masses which cause the decay products of each resultant top quark to be contained within a single high-$$p_{\mathrm {T}}$$ p T large-radius jet. The full Run 2 dataset is exploited, consisting of $$139~\hbox {fb}^{-1}$$ 139 fb - 1 of data collected from proton–proton collisions at $$\sqrt{s}=13~\mathrm {TeV}$$ s = 13 TeV from 2015 to 2018 with the ATLAS detector at the CERN Large Hadron Collider. In the absence of any significant deviation from the background expectation, lower limits on the leptoquark masses are set at $$1480~\mathrm {GeV}$$ 1480 GeV and $$1470~\mathrm {GeV}$$ 1470 GeV for the electron and muon channel, respectively.

scholarly journals Identification of boosted Higgs bosons decaying into b-quark pairs with the ATLAS detector at 13 $$\text {TeV}$$

2019 ◽  
Vol 79 (10) ◽  
Author(s):  
G. Aad ◽  
◽  
B. Abbott ◽  
D. C. Abbott ◽  
O. Abdinov ◽  
...  
Keyword(s):  
Top Quark ◽  
Hadron Collider ◽  
Atlas Detector ◽  
Higgs Bosons ◽  
Proton Collision ◽  
Jet Substructure ◽  
Proton Proton ◽  
Quark Pairs ◽  
Systematic Uncertainties ◽  
B Quark

Abstract This paper describes a study of techniques for identifying Higgs bosons at high transverse momenta decaying into bottom-quark pairs, $$H \rightarrow b\bar{b}$$H→bb¯, for proton–proton collision data collected by the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy $$\sqrt{s}=13$$s=13 $$\text {TeV}$$TeV. These decays are reconstructed from calorimeter jets found with the anti-$$k_{t}$$kt$$R = 1.0$$R=1.0 jet algorithm. To tag Higgs bosons, a combination of requirements is used: b-tagging of $$R = 0.2$$R=0.2 track-jets matched to the large-R calorimeter jet, and requirements on the jet mass and other jet substructure variables. The Higgs boson tagging efficiency and corresponding multijet and hadronic top-quark background rejections are evaluated using Monte Carlo simulation. Several benchmark tagging selections are defined for different signal efficiency targets. The modelling of the relevant input distributions used to tag Higgs bosons is studied in 36 fb$$^{-1}$$-1 of data collected in 2015 and 2016 using $$g\rightarrow b\bar{b}$$g→bb¯ and $$Z(\rightarrow b\bar{b})\gamma $$Z(→bb¯)γ event selections in data. Both processes are found to be well modelled within the statistical and systematic uncertainties.

scholarly journals Measurements of the inclusive and differential production cross sections of a top-quark–antiquark pair in association with a Z boson at $$\sqrt{s} = 13$$ TeV with the ATLAS detector

2021 ◽  
Vol 81 (8) ◽  
Author(s):  
◽  
G. Aad ◽  
B. Abbott ◽  
D. C. Abbott ◽  
A. Abed Abud ◽  
...  
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Top Quark ◽  
Production Cross ◽  
Hadron Collider ◽  
Inclusive Cross Section ◽  
Atlas Detector ◽  
Proton Collision ◽  
Proton Proton ◽  
Theoretical Predictions

AbstractMeasurements of both the inclusive and differential production cross sections of a top-quark–antiquark pair in association with a Z boson ($$t{\bar{t}}Z$$ t t ¯ Z ) are presented. The measurements are performed by targeting final states with three or four isolated leptons (electrons or muons) and are based on $$\sqrt{s} = 13$$ s = 13  TeV proton–proton collision data with an integrated luminosity of 139 $$\hbox {fb}^{-1}$$ fb - 1 , recorded from 2015 to 2018 with the ATLAS detector at the CERN Large Hadron Collider. The inclusive cross section is measured to be $$\sigma _{t{\bar{t}}Z} = 0.99 \pm 0.05$$ σ t t ¯ Z = 0.99 ± 0.05  (stat.) $$\pm \, 0.08$$ ± 0.08  (syst.) pb, in agreement with the most precise theoretical predictions. The differential measurements are presented as a function of a number of kinematic variables which probe the kinematics of the $$t{\bar{t}}Z$$ t t ¯ Z system. Both absolute and normalised differential cross-section measurements are performed at particle and parton levels for specific fiducial volumes and are compared with theoretical predictions at different levels of precision, based on a $$\chi ^{2}/$$ χ 2 / ndf and p value computation. Overall, good agreement is observed between the unfolded data and the predictions.

scholarly journals Search for electroweak production of charginos and sleptons decaying into final states with two leptons and missing transverse momentum in $$\sqrt{s}=13$$ $$\text {TeV}$$ pp collisions using the ATLAS detector

2020 ◽  
Vol 80 (2) ◽  
Author(s):  
G. Aad ◽  
◽  
B. Abbott ◽  
D. C. Abbott ◽  
O. Abdinov ◽  
...  
Keyword(s):  
Hadron Collider ◽  
Atlas Detector ◽  
Supersymmetric Particle ◽  
Final States ◽  
Proton Proton ◽  
Direct Production ◽  
Proton Collisions ◽  
Missing Transverse Momentum ◽  
The Masses ◽  
Proton Proton Collisions

Abstract A search for the electroweak production of charginos and sleptons decaying into final states with two electrons or muons is presented. The analysis is based on 139 fb$$^{-1}$$-1 of proton–proton collisions recorded by the ATLAS detector at the Large Hadron Collider at $$\sqrt{s}=13$$s=13 $$\text {TeV}$$TeV. Three R-parity-conserving scenarios where the lightest neutralino is the lightest supersymmetric particle are considered: the production of chargino pairs with decays via either W bosons or sleptons, and the direct production of slepton pairs. The analysis is optimised for the first of these scenarios, but the results are also interpreted in the others. No significant deviations from the Standard Model expectations are observed and limits at 95% confidence level are set on the masses of relevant supersymmetric particles in each of the scenarios. For a massless lightest neutralino, masses up to 420 $$\text {Ge}\text {V}$$Ge are excluded for the production of the lightest-chargino pairs assuming W-boson-mediated decays and up to 1 $$\text {TeV}$$TeV for slepton-mediated decays, whereas for slepton-pair production masses up to 700 $$\text {Ge}\text {V}$$Ge are excluded assuming three generations of mass-degenerate sleptons.

scholarly journals Search for supersymmetry in events with four or more charged leptons in 139 fb−1 of $$ \sqrt{s} $$ = 13 TeV pp collisions with the ATLAS detector

2021 ◽  
Vol 2021 (7) ◽  
Author(s):  
◽  
G. Aad ◽  
B. Abbott ◽  
D. C. Abbott ◽  
A. Abed Abud ◽  
...  
Keyword(s):  
Standard Model ◽  
Hadron Collider ◽  
New Physics ◽  
Atlas Detector ◽  
Supersymmetric Particle ◽  
Simplified Models ◽  
Final State ◽  
Proton Proton ◽  
Signal Region ◽  
Charged Leptons

Abstract A search for supersymmetry in events with four or more charged leptons (electrons, muons and τ-leptons) is presented. The analysis uses a data sample corresponding to 139 fb−1 of proton-proton collisions delivered by the Large Hadron Collider at $$ \sqrt{s} $$ s = 13 TeV and recorded by the ATLAS detector. Four-lepton signal regions with up to two hadronically decaying τ-leptons are designed to target several supersymmetric models, while a general five-lepton signal region targets any new physics phenomena leading to a final state with five charged leptons. Data yields are consistent with Standard Model expectations and results are used to set upper limits on contributions from processes beyond the Standard Model. Exclusion limits are set at the 95% confidence level in simplified models of general gauge-mediated supersymmetry, excluding higgsino masses up to 540 GeV. In R-parity-violating simplified models with decays of the lightest supersymmetric particle to charged leptons, lower limits of 1.6 TeV, 1.2 TeV, and 2.5 TeV are placed on wino, slepton and gluino masses, respectively.

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