@article{OPUS4-22614,
  title     = {Search for Higgs boson decays into pairs of light (pseudo)scalar particles in the \({γγ jj}\) final state in \({pp}\) collisions at root \(s\)=13 TeV with the ATLAS detector},
  series = {Physics Letters B},
  volume    = {782},
  journal   = {Physics Letters B},
  organization    = {The ATLAS Collaboration},
  doi       = {10.1016/j.physletb.2018.06.011},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-226147},
  pages     = {750-767},
  year      = {2018},
  abstract  = {This Letter presents a search for exotic decays of the Higgs boson to a pair of new (pseudo) scalar particles, H -> aa, where the a particle has a mass in the range 20-60 GeV, and where one of the a bosons decays into a pair of photons and the other to a pair of gluons. The search is performed in event samples enhanced in vector-boson fusion Higgs boson production by requiring two jets with large invariant mass in addition to the Higgs boson candidate decay products. The analysis is based on the full dataset of pp collisions at root s = 13 TeV recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider, corresponding to an integrated luminosity of 36.7 fb(-1). The data are in agreement with the Standard Model predictions and an upper limit at the 95\% confidence level is placed on the production cross section times the branching ratio for the decay H -> aa -> gamma gamma gg. This limit ranges from 3.1 pb to 9.0 pb depending on the mass of the a boson. (C) 2018 The Author. Published by Elsevier B.V.},
  language  = {en}
}
@article{OPUS4-22615,
  title     = {Measurement of the production cross section of three isolated photons in \({pp}\) collisions at root \(s\)=8 TeV using the ATLAS detector},
  series = {Physics Letters B},
  volume    = {781},
  journal   = {Physics Letters B},
  organization    = {The ATLAS Collaboration},
  doi       = {10.1016/j.physletb.2018.03.057},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-226154},
  pages     = {55-76},
  year      = {2018},
  abstract  = {A measurement of the production of three isolated photons in proton-proton collisions at a centre-of-mass energy root s = 8 TeV is reported. The results are based on an integrated luminosity of 20.2 fb(-1) collected with the ATLAS detector at the LHC. The differential cross sections are measured as functions of the transverse energy of each photon, the difference in azimuthal angle and in pseudorapidity between pairs of photons, the invariant mass of pairs of photons, and the invariant mass of the triphoton system. A measurement of the inclusive fiducial cross section is also reported. Next-to-leading-order perturbative QCD predictions are compared to the cross-section measurements. The predictions underestimate the measurement of the inclusive fiducial cross section and the differential measurements at low photon transverse energies and invariant masses. They provide adequate descriptions of the measurements at high values of the photon transverse energies, invariant mass of pairs of photons, and invariant mass of the triphoton system. (C) 2018 The Author. Published by Elsevier B.V.},
  language  = {en}
}
@article{OPUS4-22602,
  title     = {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},
  series = {Journal of High Energy Physics},
  volume    = {159},
  journal   = {Journal of High Energy Physics},
  number    = {10},
  organization    = {The ATLAS Collaboration},
  doi       = {10.1007/JHEP10(2018)159},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-226023},
  pages     = {1-57},
  year      = {2018},
  abstract  = {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.},
  language  = {en}
}
@article{OPUS4-22611,
  title     = {Search for flavour-changing neutral current top-quark decays \(t\) -> \({qZ}\) in proton-proton collisions at root s=13 TeV with the ATLAS detector},
  series = {Journal of High Energy Physics},
  volume    = {176},
  journal   = {Journal of High Energy Physics},
  number    = {7},
  organization    = {The ATLAS Collaboration},
  doi       = {10.1007/JHEP07(2018)176},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-226114},
  pages     = {1-40},
  year      = {2018},
  abstract  = {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.},
  language  = {en}
}
@article{OPUS4-22613,
  title     = {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},
  series = {Journal of High Energy Physics},
  volume    = {89},
  journal   = {Journal of High Energy Physics},
  number    = {7},
  organization    = {The ATLAS Collaboration},
  doi       = {10.1007/JHEP07(2018)089},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-226131},
  pages     = {1-67},
  year      = {2018},
  abstract  = {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.},
  language  = {en}
}
@article{OPUS4-22600,
  title     = {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},
  series = {Journal of High Energy Physics},
  volume    = {30},
  journal   = {Journal of High Energy Physics},
  organization    = {The ATLAS Collaboration},
  doi       = {10.1007/JHEP01(2019)030},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-226001},
  pages     = {1-48},
  year      = {2018},
  abstract  = {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.},
  language  = {en}
}
@article{OPUS4-22596,
  title     = {Comparison between simulated and observed LHC beam backgrounds in the ATLAS experiment at \(E\)\(_{beam}\)=4 TeV},
  series = {Journal of Instrumentation},
  volume    = {13},
  journal   = {Journal of Instrumentation},
  organization    = {The ATLAS Collaboration},
  doi       = {10.1088/1748-0221/13/12/P12006},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-225966},
  pages     = {1-40},
  year      = {2018},
  abstract  = {Results of dedicated Monte Carlo simulations of beam-induced background (BIB) in the ATLAS experiment at the Large Hadron Collider (LHC) are presented and compared with data recorded in 2012. During normal physics operation this background arises mainly from scattering of the 4 TeV protons on residual gas in the beam pipe. Methods of reconstructing the BIB signals in the ATLAS detector, developed and implemented in the simulation chain based on the FLUKA Monte Carlo simulation package, are described. The interaction rates are determined from the residual gas pressure distribution in the LHC ring in order to set an absolute scale on the predicted rates of BIB so that they can be compared quantitatively with data. Through these comparisons the origins of the BIB leading to different observables in the ATLAS detectors are analysed. The level of agreement between simulation results and BIB measurements by ATLAS in 2012 demonstrates that a good understanding of the origin of BIB has been reached.},
  language  = {en}
}
@article{OPUS4-22598,
  title     = {Search for W ' -> \({tb}\) decays in the hadronic final state using \({pp}\) collisions at root s=13 TeV with the ATLAS detector},
  series = {Physics Letters B},
  volume    = {781},
  journal   = {Physics Letters B},
  organization    = {The ATLAS Collaboration},
  doi       = {10.1016/j.physletb.2018.03.036},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-225987},
  pages     = {327-348},
  year      = {2018},
  abstract  = {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.},
  language  = {en}
}
@article{OPUS4-22595,
  title     = {Searches for heavy \({ZZ}\) and \({ZW}\) resonances in the \({llqq}\) and \({vvqq}\) final states in \({pp}\) collisions at root s=13 TeV with the ATLAS detector},
  series = {Journal of High Energy Physics},
  volume    = {9},
  journal   = {Journal of High Energy Physics},
  organization    = {The ATLAS Collaboration},
  doi       = {10.1007/JHEP03(2018)009},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-225951},
  pages     = {1-52},
  year      = {2018},
  abstract  = {This paper reports searches for heavy resonances decaying into ZZ or ZW using data from proton-proton collisions at a centre-of-mass energy of root s - 13 TeV. The data, corresponding to an integrated luminosity of 36.1 fb(-1), were recorded with the ATLAS detector in 2015 and 2016 at the Large Hadron Collider. The searches are performed in final states in which one Z boson decays into either a pair of light charged leptons (electrons and muons) or a pair of neutrinos, and the associated W boson or the other Z boson decays hadronically. No evidence of the production of heavy resonances is observed. Upper bounds on the production cross sections of heavy resonances times their decay branching ratios to ZZ or ZW are derived in the mass range 300-5000 GeV within the context of Standard Model extensions with additional Higgs bosons, a heavy vector triplet or warped extra dimensions. Production through gluon-gluon fusion, Drell-Yan or vector-boson fusion are considered, depending on the assumed model.},
  language  = {en}
}
@article{OPUS4-22670,
  title     = {Search for electroweak production of supersymmetric states in scenarios with compressed mass spectra at root s=13 TeV with the ATLAS detector},
  series = {Physical Review D},
  volume    = {97},
  journal   = {Physical Review D},
  number    = {5},
  organization    = {The ATLAS Collaboration},
  doi       = {10.1103/PhysRevD.97.052010},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-226707},
  pages     = {1-35},
  year      = {2018},
  abstract  = {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.},
  language  = {en}
}