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(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) A search is presented for a high-mass Higgs boson in the ..., ..., ..., and ... decay modes using the ATLAS detector at the CERN Large Hadron Collider. The search uses proton-proton collision data at a centre-of-mass energy of 8 TeV corresponding to an integrated luminosity of 20.3 fb... The results of the search are interpreted in the scenario of a heavy Higgs boson with a width that is small compared with the experimental mass resolution. The Higgs boson mass range considered extends up to ... for all four decay modes and down to as low as 140 ..., depending on the decay mode. No significant excess of events over the Standard Model prediction is found. A simultaneous fit to the four decay modes yields upper limits on the production cross-section of a heavy Higgs boson times the branching ratio to ... boson pairs. 95 % confidence level upper limits range from 0.53 pb at ... GeV to 0.008 pb at ... GeV for the gluon-fusion production mode and from 0.31 pb at ... GeV to 0.009 pb at ... GeV for the vector-boson-fusion production mode. The results are also interpreted in the context of Type-I and Type-II two-Higgs-doublet models.

A search is presented for the pair production of heavy vector-like B quarks, primarily targeting B quark decays into a W boson and a top quark. The search is based on 36.1 fb−1 of pp collisions at s=13 TeV recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. Data are analysed in the lepton-plus-jets final state, characterised by a high-transverse-momentum isolated electron or muon, large missing transverse momentum, and multiple jets, of which at least one is b-tagged. No significant deviation from the Standard Model expectation is observed. The 95% confidence level lower limit on the B mass is 1350 GeV assuming a 100% branching ratio to Wt. In the SU(2) singlet scenario, the lower mass limit is 1170 GeV. The 100% branching ratio limits are found to be also applicable to heavy vector-like X production, with charge +5/3, that decay into Wt. This search is also sensitive to a heavy vector-like B quark decaying into other final states (Zb and Hb) and thus mass limits on B production are set as a function of the decay branching ratios.

Cross-sections of associated production of a Higgs boson decaying into bottomquark pairs and an electroweak gauge boson, W or Z, decaying into leptons are measured as a function of the gauge boson transverse momentum. The measurements are performed in kinematic fiducial volumes defined in the ‘simplified template cross-section’ framework. The results are obtained using 79.8 fb−1 of proton-proton collisions recorded by the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy of 13 TeV. All measurements are found to be in agreement with the Standard Model predictions, and limits are set on the parameters of an effective Lagrangian sensitive to modifications of the Higgs boson couplings to the electroweak gauge bosons.

Abstract A search for a high-mass Higgs boson H is performed in the H [arrow right] WW [arrow right] νν and H [arrow right] WW [arrow right] νqq decay channels using pp collision data corresponding to an integrated luminosity of 20.3 fb-1 collected at ... TeV by the ATLAS detector at the Large Hadron Collider. No evidence of a high-mass Higgs boson is found. Limits on [sigma] H × BR(H [arrow right] WW) as a function of the Higgs boson mass m H are determined in three different scenarios: one in which the heavy Higgs boson has a narrow width compared to the experimental resolution, one for a width increasing with the boson mass and modeled by the complex-pole scheme following the same behavior as in the Standard Model, and one for intermediate widths. The upper range of the search is m H = 1500 GeV for the narrow-width scenario and m H = 1000 GeV for the other two scenarios. The lower edge of the search range is 200-300 GeV and depends on the analysis channel and search scenario. For each signal interpretation, individual and combined limits from the two WW decay channels are presented. At m H = 1500 GeV, the highest-mass point tested, [sigma] H × BR(H [arrow right] WW) for a narrow-width Higgs boson is constrained to be less than 22 fb and 6.6 fb at 95% CL for the gluon fusion and vector-boson fusion production modes, respectively. [Figure not available: see fulltext.]

The algorithms used by the ATLAS Collaboration during Run 2 of the Large Hadron Collider to identify jets containing b-hadrons are presented. The performance of the algorithms is evaluated in the simulation and the efficiency with which these algorithms identify jets containing b-hadrons is measured in collision data. The measurement uses a likelihood-based method in a sample highly enriched in \\[t{\\bar{t}}\\] events. The topology of the \\[t \\rightarrow W b\\] decays is exploited to simultaneously measure both the jet flavour composition of the sample and the efficiency in a transverse momentum range from 20 to 600 GeV. The efficiency measurement is subsequently compared with that predicted by the simulation. The data used in this measurement, corresponding to a total integrated luminosity of 80.5 \\[\\hbox {fb}^{-1}\\], were collected in proton–proton collisions during the years 2015–2017 at a centre-of-mass energy \\[\\sqrt{s}=\\] 13 TeV. By simultaneously extracting both the efficiency and jet flavour composition, this measurement significantly improves the precision compared to previous results, with uncertainties ranging from 1 to 8% depending on the jet transverse momentum.

A measurement of \\[W^\\pm \\] boson production in Pb+Pb collisions at \\[\\sqrt{s_\\mathrm {NN}} = 5.02~\\text {Te}\\text {V}\\] is reported using data recorded by the ATLAS experiment at the LHC in 2015, corresponding to a total integrated luminosity of \\[0.49\\;\\mathrm {nb^{-1}}\\]. The \\[W^\\pm \\] bosons are reconstructed in the electron or muon leptonic decay channels. Production yields of leptonically decaying \\[W^\\pm \\] bosons, normalised by the total number of minimum-bias events and the nuclear thickness function, are measured within a fiducial region defined by the detector acceptance and the main kinematic requirements. These normalised yields are measured separately for \\[W^+\\] and \\[W^-\\] bosons, and are presented as a function of the absolute value of pseudorapidity of the charged lepton and of the collision centrality. The lepton charge asymmetry is also measured as a function of the absolute value of lepton pseudorapidity. In addition, nuclear modification factors are calculated using the \\[W^\\pm \\] boson production cross-sections measured in pp collisions. The results are compared with predictions based on next-to-leading-order calculations with CT14 parton distribution functions as well as with predictions obtained with the EPPS16 and nCTEQ15 nuclear parton distribution functions. No dependence of normalised production yields on centrality and a good agreement with predictions are observed for mid-central and central collisions. For peripheral collisions, the data agree with predictions within 1.7 (0.9) standard deviations for \\[W^-\\] (\\[W^+\\]) bosons.

The production cross-sections for \\[W^{\\pm }\\] and Z bosons are measured using ATLAS data corresponding to an integrated luminosity of 4.0 pb\\[^{-1}\\] collected at a centre-of-mass energy \\[\\sqrt{s}=2.76\\] TeV. The decay channels \\[W \\rightarrow \\ell \\nu \\] and \\[Z \\rightarrow \\ell \\ell \\] are used, where \\[\\ell \\] can be an electron or a muon. The cross-sections are presented for a fiducial region defined by the detector acceptance and are also extrapolated to the full phase space for the total inclusive production cross-section. The combined (average) total inclusive cross-sections for the electron and muon channels are: \\[\\begin{aligned} \\sigma ^{\\text {tot}}_{W^{+}\\rightarrow \\ell \\nu }= & {} 2312 \\pm 26\\ (\\text {stat.})\\\&\\pm 27\\ (\\text {syst.}) \\pm 72\\ (\\text {lumi.}) \\pm 30\\ (\\text {extr.})~\\text {pb} , \\\ \\sigma ^{\\text {tot}}_{W^{-}\\rightarrow \\ell \\nu }= & {} 1399 \\pm 21\\ (\\text {stat.})\\ \\pm 17\\ (\\text {syst.}) \\\&\\pm 43\\ (\\text {lumi.}) \\pm 21\\ (\\text {extr.})~\\text {pb} , \\\ \\sigma ^{\\text {tot}}_{Z \\rightarrow \\ell \\ell }= & {} 323.4 \\pm 9.8\\ (\\text {stat.}) \\pm 5.0\\ (\\text {syst.})\\\&\\pm 10.0\\ (\\text {lumi.}) \\pm 5.5 (\\text {extr.}) ~\\text {pb} . \\end{aligned}\\]Measured ratios and asymmetries constructed using these cross-sections are also presented. These observables benefit from full or partial cancellation of many systematic uncertainties that are correlated between the different measurements.

A measurement of fiducial and differential cross-sections for \\[W^+W^-\\] production in proton–proton collisions at \\[\\sqrt{s}=13\\] TeV with the ATLAS experiment at the Large Hadron Collider using data corresponding to an integrated luminosity of 36.1 \\[\\hbox {fb}^{-1}\\] is presented. Events with one electron and one muon are selected, corresponding to the decay of the diboson system as \\[WW\\rightarrow e^{\\pm }\\nu \\mu ^{\\mp }\\nu \\]. To suppress top-quark background, events containing jets with a transverse momentum exceeding 35 GeV are not included in the measurement phase space. The fiducial cross-section, six differential distributions and the cross-section as a function of the jet-veto transverse momentum threshold are measured and compared with several theoretical predictions. Constraints on anomalous electroweak gauge boson self-interactions are also presented in the framework of a dimension-six effective field theory.

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}\\], for proton–proton collision data collected by the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy \\[\\sqrt{s}=13\\] \\[\\text {TeV}\\]. These decays are reconstructed from calorimeter jets found with the anti-\\[k_{t}\\]\\[R = 1.0\\] jet algorithm. To tag Higgs bosons, a combination of requirements is used: b-tagging of \\[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}\\] of data collected in 2015 and 2016 using \\[g\\rightarrow b\\bar{b}\\] and \\[Z(\\rightarrow b\\bar{b})\\gamma \\] event selections in data. Both processes are found to be well modelled within the statistical and systematic uncertainties.

A search for excited electrons produced in pp collisions at \\[\\sqrt{s}\\] = 13 \\[\\text {Te}\\text {V}\\] via a contact interaction \\[q{\\bar{q}}\\rightarrow ee^*\\] is presented. The search uses 36.1 fb\\[^{-1}\\] of data collected in 2015 and 2016 by the ATLAS experiment at the Large Hadron Collider. Decays of the excited electron into an electron and a pair of quarks (\\[eq{\\bar{q}}\\]) are targeted in final states with two electrons and two hadronic jets, and decays via a gauge interaction into a neutrino and a \\[W\\] boson (\\[\\nu W\\]) are probed in final states with an electron, missing transverse momentum, and a large-radius jet consistent with a hadronically decaying \\[W\\] boson. No significant excess is observed over the expected backgrounds. Upper limits are calculated for the \\[pp \\rightarrow ee^*\\rightarrow eeq{\\bar{q}} \\] and \\[pp \\rightarrow ee^*\\rightarrow e\\nu W \\] production cross sections as a function of the excited electron mass \\[m_{e^*}\\] at 95% confidence level. The limits are translated into lower bounds on the compositeness scale parameter \\[\\Lambda \\] of the model as a function of \\[m_{e^*}\\]. For \\[m_{e^*} <0.5\\] \\[\\text {Te}\\text {V}\\], the lower bound for \\[\\Lambda \\] is 11 \\[\\text {Te}\\text {V}\\]. In the special case of \\[m_{e^*} =\\Lambda \\], the values of \\[m_{e^*} <4.8\\] \\[\\text {Te}\\text {V}\\] are excluded. The presented limits on \\[\\Lambda \\] are more stringent than those obtained in previous searches.