TY - JOUR T1 - Search for the standard model Higgs boson produced in association with top quarks and decaying into a b(b)overbar pair in \(pp\) collisions at root \(s\)=13 TeV with the ATLAS detector JF - Physical Review D N2 - A search for the standard model Higgs boson produced in association with a top-quark pair, t(t)overbarH, is presented. The analysis uses 36.1 fb(-1) of pp collision data at root s = 13 TeV collected with the ATLAS detector at the Large Hadron Collider in 2015 and 2016. The search targets the H -> b(b)overbar decay mode. The selected events contain either one or two electrons or muons from the top-quark decays, and are then categorized according to the number of jets and how likely these are to contain b-hadrons. Multivariate techniques are used to discriminate between signal and background events, the latter being dominated by ft + jets production. For a Higgs boson mass of 125 GeV, the ratio of the measured t(t)overbarH signal cross-section to the standard model expectation is found to be mu = 0.84(-0.61)(+0.64). A value of mu greater than 2.0 is excluded at 95% confidence level (C.L.) while the expected upper limit is mu < 1.2 in the absence of a t(t)overbarH signal. KW - ++ KW - Symmetries KW - program KW - MASS KW - spontaneous symmetry breaking KW - Higgs bosons KW - Top quark Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-226545 VL - 97 IS - 7 ER - TY - JOUR T1 - Search for W ' -> \({tb}\) decays in the hadronic final state using \({pp}\) collisions at root s=13 TeV with the ATLAS detector JF - Physics Letters B N2 - A search for W'-boson production in the W' -> t (b) over bar -> q (q) over bar 'b (b) over bar decay channel is presented using 36.1 fb(-1) of 13 TeV proton-proton collision data collected by the ATLAS detector at the Large Hadron Collider in 2015 and 2016. The search is interpreted in terms of both a left-handed and a right-handed chiral W' boson within the mass range 1-5 TeV. Identification of the hadronically decaying top quark is performed using jet substructure tagging techniques based on a shower deconstruction algorithm. No significant deviation from the Standard Model prediction is observed and the results are expressed as upper limits on the W' -> t (b) over bar production cross-section times branching ratio as a function of the W'-boson mass. These limits exclude W' bosons with right-handed couplings with masses below 3.0 TeV and W' bosons with left-handed couplings with masses below 2.9 TeV, at the 95% confidence level. (C) 2018 The Author. Published by Elsevier B.V. KW - Symmetry-breaking KW - Pair production KW - ++ KW - Dynamics KW - Physics KW - Mass Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-225987 VL - 781 ER - TY - JOUR T1 - Search for new phenomena using the invariant mass distribution of same-flavour opposite-sign dilepton pairs in events with missing transverse momentum in root \(s\)=13 TeV \(pp\) collisions with the ATLAS detector JF - European Physical Journal C N2 - A search for new phenomena in final states containing an e(+)e(-) or m(+)m(-) pair, jets, and large missing transverse momentum is presented. This analysis makes use of proton-proton collision data with an integrated luminosity of 36.1 fb(-1), collected during 2015 and 2016 at a centre of-mass energy Os = 13 TeV with the ATLAS detector at the Large Hadron Collider. The search targets the pair production of supersymmetric coloured particles (squarks or gluinos) and their decays into final states containing an e(+)e(-) or m(+)m(-) pair and the lightest neutralino ((c) over tilde (0)(1)) via one of two next-to-lightest neutralino ((c) over tilde (0)(2)) decay mechanisms: (c) over tilde (0)(2) Z (c) over tilde (0)(1), where the Z boson decays leptonically leading to a peak in the dilepton invariant mass distribution around the Z boson mass; and (c) over tilde (0)(2) l(+)1(-) (c) over tilde (0)(1) with no intermediate l(+)l(-) resonance, yielding a kinematic endpoint in the dilepton invariant mass spectrum. The data are found to be consistent with the Standard Model expectation. Results are interpreted using simplified models, and exclude gluinos and squarks with masses as large as 1.85 and 1.3 TeV at 95% confidence level, respectively. KW - Parton Distributions KW - Gluino Production KW - ++ KW - Extension KW - Energy KW - Squark KW - Supersymmetry KW - Physics KW - Decay Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-226109 VL - 78 ER - TY - JOUR T1 - Search for High-Mass Resonances Decaying to τν in \(pp\) Collisions at root \(s\)=13 TeV with the ATLAS Detector JF - Physical Review Letters N2 - A search for high-mass resonances decaying to tau nu using proton-proton collisions at root s = 13 TeV produced by the Large Hadron Collider is presented. Only tau-lepton decays with hadrons in the final state are considered. The data were recorded with the ATLAS detector and correspond to an integrated luminosity of 36.1 fb(-1). No statistically significant excess above the standard model expectation is observed; model-independent upper limits are set on the visible tau nu production cross section. Heavy W' bosons with masses less than 3.7 TeV in the sequential standard model and masses less than 2.2-3.8 TeV depending on the coupling in the nonuniversal Go(221) model are excluded at the 95% credibility level. KW - Proton-Proton Collisions KW - Parton Ditributions KW - Cross-Section KW - ++ KW - Lepton KW - Hadron colliders KW - Hypothetical gauge bosons KW - Particle production KW - Extensions of gauge sector Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-226556 VL - 120 ER - TY - JOUR T1 - Search for \({WW/WZ}\) resonance production in \(lvqq\) final states in \(pp\) collisions at root \(s\)=13 TeV with the ATLAS detector JF - Journal of High Energy Physics N2 - A search is conducted for new resonances decaying into a WW or WZ boson pair, where one W boson decays leptonically and the other W or Z boson decays hadronically. It is based on proton-proton collision data with an integrated luminosity of 36.1 fb(-1) collected with the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy of root s = 13 TeV in 2015 and 2016. The search is sensitive to diboson resonance production via vector-boson fusion as well as quark-antiquark annihilation and gluon-gluon fusion mechanisms. No significant excess of events is observed with respect to the Standard Model backgrounds. Several benchmark models are used to interpret the results. Limits on the production cross section are set for a new narrow scalar resonance, a new heavy vector-boson and a spin-2 Kaluza-Klein graviton. KW - Hadron-Hadron scattering (experiments) KW - ++ KW - HIGGS Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-226787 VL - 42 ER - TY - JOUR T1 - Search for electroweak production of supersymmetric states in scenarios with compressed mass spectra at root s=13 TeV with the ATLAS detector JF - Physical Review D N2 - A search for electroweak production of supersymmetric particles in scenarios with compressed mass spectra in final states with two low-momentum leptons and missing transverse momentum is presented. This search uses proton-proton collision data recorded by the ATLAS detector at the Large Hadron Collider in 2015-2016, corresponding to 36.1 tb(-1) of integrated luminosity at root s = 13 TeV. Events with same flavor pairs of electrons or muons with opposite electric charge are selected. The data are found to be consistent with the Standard Model prediction. Results are interpreted using simplified models of R-parity conserving supersymmetry in which there is a small mass difference between the masses of the produced supersymmetric particles and the lightest neutralino. Exclusion limits at 95% confidence level are set on next-to-lightest neutralino masses of up to 145 GeV for Higgsino production and 175 GeV for wino production, and slepton masses of up to 190 GeV for pair production of sleptons. In the compressed mass regime, the exclusion limits extend down to mass splittings of 2.5 GeV for Higgsino production, 2 GeV for wino production, and 1 GeV for slepton production. The results are also interpreted in the context of a radiatively-driven natural supersymmetry model with nonuniversal Higgs boson masses. KW - PP Collicions KW - Parton Distributions KW - Gluino Production KW - Measuring Masses KW - Cross-Section KW - ++ KW - Z Boson KW - Energy KW - Squark KW - Extension Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-226707 VL - 97 IS - 5 ER - TY - JOUR T1 - Search for pair production of up-type vector-like quarks and for four-top-quark events in final states with multiple \(b\)-jets with the ATLAS detector JF - Journal of High Energy Physics N2 - A search for pair production of up-type vector-like quarks (T) with a significant branching ratio into a top quark and either a Standard Model Higgs boson or a Z boson is presented. The same analysis is also used to search for four-top-quark production in several new physics scenarios. The search is based on a dataset of pp collisions at root s = 13TeV recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider and corresponds to an integrated luminosity of 36.1 fb(-1). Data are analysed in the lepton+jets final state, characterised by an isolated electron or muon with high transverse momentum, large missing transverse momentum and multiple jets, as well as the jets+E-T(miss) final state, characterised by multiple jets and large missing transverse momentum. The search exploits the high multiplicity of jets identified as originating from b-quarks, and the presence of boosted, hadronically decaying top quarks and Higgs bosons reconstructed as large-radius jets, characteristic of signal events. No significant excess above the Standard Model expectation is observed, and 95% CL upper limits are set on the production cross sections for the different signal processes considered. These cross-section limits are used to derive lower limits on the mass of a vector-like T quark under several branching ratio hypotheses assuming contributions from T -> Wb, Zt, Ht decays. The 95% CL observed lower limits on the T quark mass range between 0.99TeV and 1.43TeV for all possible values of the branching ratios into the three decay modes considered, significantly extending the reach beyond that of previous searches. Additionally, upper limits on anomalous four-top-quark production are set in the context of an effective field theory model, as well as in an universal extra dimensions model. KW - Beyond Standard Model KW - Hadron-Hadron scattering (experiments) KW - vector-like quarks KW - Parton Distributions KW - ++ KW - Boson KW - Breaking KW - Program KW - Gluon Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-226131 VL - 89 IS - 7 ER - TY - JOUR T1 - Search for pair production of Higgs bosons in the \({bb̅bb̅}\) final state using proton-proton collisions at root s=13 TeV with the ATLAS detector JF - Journal of High Energy Physics N2 - A search for Higgs boson pair production in the bbbb final state is carried out with up to 36.1 fb(-1) of LHC proton-proton collision data collected at s=13 TeV with the ATLAS detector in 2015 and 2016. Three benchmark signals are studied: a spin-2 graviton decaying into a Higgs boson pair, a scalar resonance decaying into a Higgs boson pair, and Standard Model non-resonant Higgs boson pair production. Two analyses are carried out, each implementing a particular technique for the event reconstruction that targets Higgs bosons reconstructed as pairs of jets or single boosted jets. The resonance mass range covered is 260-3000 GeV. The analyses are statistically combined and upper limits on the production cross section of Higgs boson pairs times branching ratio to bbbb are set in each model. No significant excess is observed; the largest deviation of data over prediction is found at a mass of 280 GeV, corresponding to 2.3 standard deviations globally. The observed 95% confidence level upper limit on the non-resonant production is 13 times the Standard Model prediction. KW - Hadron-Hadron scattering (experiments) KW - ++ KW - LHC Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-226001 VL - 30 ER - TY - JOUR T1 - Measurements of differential cross sections of top quark pair production in association with jets in pp collisions at root s=13 TeV using the ATLAS detector JF - Journal of High Energy Physics N2 - Measurements of di ff erential cross sections of top quark pair production in association with jets by the ATLAS experiment at the LHC are presented. The measurements are performed as functions of the top quark transverse momentum, the transverse momentum of the top quark-antitop quark system and the out-of-plane transverse momentum using data from pp collisions at p s = 13TeV collected by the ATLAS detector at the LHC in 2015 and corresponding to an integrated luminosity of 3.2 fb. The top quark pair events are selected in the lepton (electron or muon) + jets channel. The measured cross sections, which are compared to several predictions, allow a detailed study of top quark production. KW - Hadron-Hadron scattering (experiments) KW - Jets KW - Top physics KW - Parton Distributions KW - ++ Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-226023 VL - 159 IS - 10 ER - TY - JOUR T1 - Search for flavour-changing neutral current top-quark decays \(t\) -> \({qZ}\) in proton-proton collisions at root s=13 TeV with the ATLAS detector JF - Journal of High Energy Physics N2 - A search for flavour-changing neutral-current processes in top-quark decays is presented. Data collected with the ATLAS detector from proton-proton collisions at the Large Hadron Collider at a centre-of-mass energy of root s = 13TeV, corresponding to an integrated luminosity of 36.1 fb(-1), are analysed. The search is performed using top-quark pair events, with one top quark decaying through the t -> qZ (q = u, c) flavour-changing neutral-current channel, and the other through the dominant Standard Model mode t -> bW. Only Z boson decays into charged leptons and leptonic W boson decays are considered as signal. Consequently, the final-state topology is characterized by the presence of three isolated charged leptons (electrons or muons), at least two jets, one of the jets originating from a b-quark, and missing transverse momentum from the undetected neutrino. The data are consistent with Standard Model background contributions, and at 95% confidence level the search sets observed (expected) upper limits of 1.7 x 10(-4) (2.4 x 10(-4)) on the t -> uZ branching ratio and 2.4 x 10(-4) (3.2 x 10(-4)) on the t -> cZ branching ratio, constituting the most stringent limits to date. KW - Hadron-Hadron scattering (experiments) KW - Parton Distributions KW - ++ KW - Pair-Production KW - Cross-Section KW - Physics KW - Models Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-226114 VL - 176 IS - 7 ER -