This paper presents a search for direct top squark pair production in events with missing transverse momentum plus either a pair of jets consistent with Standard Model Higgs boson decay into b-quarks or a same-flavour opposite-sign dilepton pair with an invariant mass consistent with a Z boson. The analysis is performed using the proton–proton collision data at \n$$\\sqrt{s}=13$$\n\n TeV collected with the ATLAS detector during the LHC Run-2, corresponding to an integrated luminosity of 139 fb\n$$^{-1}$$\n\n. No excess is observed in the data above the Standard Model predictions. The results are interpreted in simplified models featuring direct production of pairs of either the lighter top squark (\n$$\\tilde{t}_1$$\n\n) or the heavier top squark (\n$$\\tilde{t}_2$$\n\n), excluding at 95% confidence level \n$$\\tilde{t}_1$$\n\n and \n$$\\tilde{t}_2$$\n\n masses up to about 1220 and 875 GeV, respectively.

A search is conducted for the electroweak pair production of a chargino and a neutralino pp -> (chi) over tilde (+/-)(1)(chi) over tilde (0)(2), where the chargino decays into the lightest neutralino and a W boson, (chi) over tilde (+/-)(1) -> (chi) over tilde W-0(1)+/- while the neutralino decays into the lightest neutralino and a Standard Model-like 125 GeV Higgs boson,(chi) over tilde (0)(2) -> (chi) over tilde (0)(1)h. Fully hadronic, semileptonic, diphoton, and multilepton (electrons, muons) final. states with missing transverse momentum are considered in this search. Higgs bosons in the final state are identified by either two jets originating from bottom quarks (h -> b (b) over bar), two photons (h -> gamma gamma), or leptons from the decay modes h -> WW, h -> ZZ or h -> tau tau. The analysis is based on 36.1 fb(-1) of s root s = 13 TeV proton-proton collision data recorded by the ATLAS detector at the Large Hadron Collider. Observations are consistent with the Standard Model expectations, and 95% confidence-level limits of up to 680 GeV in (chi) over tilde (+/-)(1)/(chi) over tilde (0)(2) mass are set in the context of a simplified supersymmetric model.

This Letter presents a search for heavy charged long-lived particles produced in proton–proton collisions at √ s = 13 TeV at the LHC using a data sample corresponding to an integrated luminosity of 36 . 1 fb − 1 collected by the ATLAS experiment in 2015 and 2016. These particles are expected to travel with a velocity significantly below the speed of light, and therefore have a specific ionisation higher than any high-momentum Standard Model particle of unit charge. The pixel subsystem of the ATLAS detector is used in this search to measure the ionisation energy loss of all reconstructed charged particles which traverse the pixel detector. Results are interpreted assuming the pair production of R -hadrons as composite colourless states of a long-lived gluino and Standard Model partons. No significant deviation from Standard Model background expectations is observed, and lifetime-dependent upper limits on R -hadron production cross-sections and gluino masses are set, assuming the gluino always decays to two quarks and a 100 GeV stable neutralino. R -hadrons with lifetimes above 1.0 ns are excluded at the 95% confidence level, with lower limits on the gluino mass ranging between 1290 GeV and 2060 GeV. In the case of stable R -hadrons, the lower limit on the gluino mass at the 95% confidence level is 1890 GeV. © 2018 The Author. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP 3 .

Measurements of fiducial integrated and differential cross sections for inclusive $W^+$ , $W^-$ and Z boson production are reported. They are based on $25.0 \\pm 0.5\\, \\mathrm {pb}^{-1}$ of pp collision data at $\\sqrt{s} = 5.02$ TeV collected with the ATLAS detector at the CERN Large Hadron Collider. Electron and muon decay channels are analysed, and the combined $W^+$ , $W^-$ and Z integrated cross sections are found to be $\\sigma _{W^+}= 2266 \\pm 9~\\text {(stat)} \\pm 29~\\text {(syst)} \\pm 43~\\text {(lumi)}$ pb, $\\sigma _{W^-}= 1401 \\pm 7~\\text {(stat)} \\pm 18~\\text {(syst)} \\pm 27~\\text {(lumi)}$ pb, and $\\sigma _Z= 374.5 \\pm 3.4~\\text {(stat)} \\pm 3.6~\\text {(syst)} \\pm 7.0~\\text {(lumi)}$ pb, in good agreement with next-to-next-to-leading-order QCD cross-section calculations. These measurements serve as references for Pb+Pb interactions at the LHC at $\\sqrt{s_{\\mathrm {NN}}}=5.02$ TeV.

A measurement of off-shell Higgs boson production in the ZZ -> 4l and ZZ -> 2l2v decay channels, where stands for either an electron or a muon, is performed using data from proton-proton collisions at a centre-of-mass energy of root s = 13 TeV. The data were collected by the ATLAS experiment in 2015 and 2016 at the Large Hadron Collider, and they correspond to an integrated luminosity of 36.1 fb(-1). An observed (expected) upper limit on the off-shell Higgs signal strength, defined as the event yield normalised to the Standard Model prediction, of 3.8 (3.4) is obtained at 95% confidence level (CL). Assuming the ratio of the Higgs boson couplings to the Standard Model predictions is independent of the momentum transfer of the Higgs production mechanism considered in the analysis, a combination with the on-shell signal-strength measurements yields an observed (expected) 95% CL upper limit on the Higgs boson total width of 14.4 (15.2) MeV. (C) 2018 The Author. Published by Elsevier B.V.

A search for new charged massive gauge bosons, W′, is performed with the ATLAS detector at the LHC. Data were collected in proton–proton collisions at a center-of-mass energy of s=13 TeV and correspond to an integrated luminosity of 36.1 fb−1. This analysis searches for W′ bosons in the W′→tb¯ decay channel in final states with an electron or muon plus jets. The search covers resonance masses between 0.5 and 5.0 TeV and considers right-handed W′ bosons. No significant deviation from the Standard Model (SM) expectation is observed and upper limits are set on the W′→tb¯ cross section times branching ratio and the W′ boson effective couplings as a function of the W′ boson mass. For right-handed W′ bosons with coupling to the SM particles equal to the SM weak coupling constant, masses below 3.15 TeV are excluded at the 95% confidence level. This search is also combined with a previously published ATLAS result for W′→tb¯ in the fully hadronic final state. Using the combined searches, right-handed W′ bosons with masses below 3.25 TeV are excluded at the 95% confidence level. © 2018 The Author(s)

A search for the decay of the Standard Model Higgs boson into a b ¯ b pair when produced in association with a W or Z boson is performed with the ATLAS detector. The data, corresponding to an integrated luminosity of 79 . 8 fb − 1 were collected in proton–proton collisions during Run 2 of the Large Hadron Collider at a centre-of-mass energy of 13 TeV. For a Higgs boson mass of 125 GeV, an excess of events over the expected background from other Standard Model processes is found with an observed (expected) significance of 4.9 (4.3) standard deviations. A combination with the results from other searches in Run 1 and in Run 2 for the Higgs boson in the b ¯ b decay mode is performed, which yields an observed (expected) significance of 5.4 (5.5) standard deviations, thus providing direct observation of the Higgs boson decay into b -quarks. The ratio of the measured event yield for a Higgs boson decaying into b ¯ b to the Standard Model expectation is 1 . 01 ± 0 . 12 ( stat .) + 0 . 16 − 0 . 15 ( syst .) . Additionally, a combination of Run 2 results searching for the Higgs boson produced in association with a vector boson yields an observed (expected) significance of 5.3 (4.8) standard deviations. © 2018 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP 3 .

A measurement of production cross sections of the Higgs boson in proton-proton collisions is presentedin the H → ττ decay channel. The analysis is performed using 36.1 fb−1 of data recorded by the ATLASexperiment at the Large Hadron Collider at a center-of-mass energy of ffiffis p ¼ 13 TeV. All combinations ofleptonic (τ → lvv¯ with l ¼ e; μ) and hadronic (τ → hadrons v) τ decays are considered. The H → ττsignal over the expected background from other Standard Model processes is established with an observed(expected) significance of 4.4 (4.1) standard deviations. Combined with results obtained using data taken at7 and 8 TeV center-of-mass energies, the observed (expected) significance amounts to 6.4 (5.4) standarddeviations and constitutes an observation of H → ττ decays. Using the data taken at ffiffis p ¼ 13 TeV, thetotal cross section in the H → ττ decay channel is measured to be 3.77þ0.60 −0.59 ðstatÞ þ0.87 −0.74 ðsystÞ pb, for aHiggs boson of mass 125 GeV assuming the relative contributions of its production modes aspredicted by the Standard Model. Total cross sections in the H → ττ decay channel are determinedseparately for vector-boson-fusion production and gluon-gluon-fusion production to be σVBFH→ττ ¼ 0.280.09 ðstatÞ þ0.11 −0.09 ðsystÞ pb and σggFH→ττ ¼ 3.1 1.0 ðstatÞ þ1.6 −1.3 ðsystÞ pb, respectively. Similarly, results of a fitare reported in the framework of simplified template cross sections. All measurements are in agreementwith Standard Model expectations.

A search for resonant and nonresonant pair production of Higgs bosons in the bb¯τ+τ- final state is presented. The search uses 36.1  fb-1 of pp collision data with s=13  TeV recorded by the ATLAS experiment at the LHC in 2015 and 2016. Decays of the τ-lepton pairs with at least one τ lepton decaying to final states with hadrons and a neutrino are considered. No significant excess above the expected background is observed in the data. The cross-section times branching ratio for nonresonant Higgs boson pair production is constrained to be less than 30.9 fb, 12.7 times the standard model expectation, at 95% confidence level. The data are also analyzed to probe resonant Higgs boson pair production, constraining a model with an extended Higgs sector based on two doublets and a Randall-Sundrum bulk graviton model. Upper limits are placed on the resonant Higgs boson pair production cross-section times branching ratio, excluding resonances X in the mass range 305  GeV<mX<402  GeV in the simplified hMSSM minimal supersymmetric model for tanβ=2 and excluding bulk Randall-Sundrum gravitons GKK in the mass range 325  GeV<mGKK<885  GeV for k/M¯Pl=1.

A search for pair production of the supersymmetric partners of the Higgs boson (higgsinos ˜H) in gauge-mediated scenarios is reported. Each higgsino is assumed to decay to a Higgs boson and a gravitino. Two complementary analyses, targeting high- and low-mass signals, are performed to maximize sensitivity. The two analyses utilize LHC pp collision data at a center-of-mass energy √s=13  TeV, the former with an integrated luminosity of 36.1  fb−1 and the latter with 24.3  fb−1, collected with the ATLAS detector in 2015 and 2016. The search is performed in events containing missing transverse momentum and several energetic jets, at least three of which must be identified as b-quark jets. No significant excess is found above the predicted background. Limits on the cross section are set as a function of the mass of the ˜H in simplified models assuming production via mass-degenerate higgsinos decaying to a Higgs boson and a gravitino. Higgsinos with masses between 130 and 230 GeV and between 290 and 880 GeV are excluded at the 95% confidence level. Interpretations of the limits in terms of the branching ratio of the higgsino to a Z boson or a Higgs boson are also presented, and a 45% branching ratio to a Higgs boson is excluded for m˜H≈400  GeV.