TY - JOUR T1 - Search for Higgs boson pair production in the b\(\overline{b}\)b\(\overline{b}\) final state from pp collisions at \(\sqrt {s}\) = 8 TeV with the ATLAS detector JF - European Physical Journal C: Particles and Fields N2 - A search for Higgs boson pair production pp → hh is performed with 19.5 fb\(^{−1}\) of proton–proton collision data at \(\sqrt {s}\) = 8 TeV, which were recorded by the ATLAS detector at the Large Hadron Collider in 2012. The decay products of each Higgs boson are reconstructed as a high-momentum b\(\overline{b}\) system with either a pair of small-radius jets or a single large-radius jet, the latter exploiting jet substructure techniques and associated b-tagged track-jets. No evidence for resonant or non-resonant Higgs boson pair production is observed. The data are interpreted in the context of the Randall–Sundrum model with a warped extra dimension as well as the two-Higgs-doublet model. An upper limit on the cross-section for pp → G\(^{*}_{KK}\) → hh → b\(\overline{b}\)b\(\overline{b}\) of 3.2(2.3) fb is set for a Kaluza–Klein graviton G\(^{*}_{KK}\) mass of 1.0(1.5) TeV, at the 95 % confidence level. The search for non-resonant Standard Model hh production sets an observed 95 % confidence level upper limit on the production cross-section σ(pp → hh → b\(\overline{b}\)b\(\overline{b}\)) of 202 fb, compared to a Standard Model prediction of σ(pp → hh → b\(\overline{b}\)b\(\overline{b}\)) = 3.6±0.5 fb. KW - Higgs boson KW - proton-proton collision KW - ATLAS detector KW - pair production Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-150119 VL - 75 IS - 9 ER - TY - JOUR T1 - Search for heavy long-lived multi-charged particles in pp collisions at \(\sqrt {s}\) = 8 TeV using the ATLAS detector JF - European Physical Journal C: Particles and Fields N2 - A search for heavy long-lived multi-charged particles is performed using the ATLAS detector at the LHC. Data collected in 2012 at \(\sqrt {s}\) = 8 TeV from pp collisions corresponding to an integrated luminosity of 20.3 fb\(^{−1}\) are examined. Particles producing anomalously high ionisation, consistent with long-lived massive particles with electric charges from |q| = 2e to |q| = 6e are searched for. No signal candidate events are observed, and 95 % confidence level cross-section upper limits are interpreted as lower mass limits for a Drell–Yan production model. The mass limits range between 660 and 785 GeV. KW - ATLAS detector KW - proton-proton collision Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-150100 VL - 75 IS - 8 ER - TY - JOUR T1 - Search for direct pair production of a chargino and a neutralino decaying to the 125 GeV Higgs boson in \(\sqrt {s}\) = 8 TeV pp collisions with the ATLAS detector JF - European Physical Journal C: Particles and Fields N2 - A search is presented for the direct pair production of a chargino and a neutralino pp → \(\tilde{χ}\)\(^{±}_{1}\)\(\tilde{χ}\)\(^{0}_{2}\), where the chargino decays to the lightest neutralino and the W boson, \(\tilde{χ}\)\(^{±}_{1}\)→\(\tilde{χ}\)\(^{0}_{1}\)(W\(^{±}\)→ℓ\(^{±}\)ν), while the neutralino decays to the lightest neutralino and the 125 GeV Higgs boson, \(\tilde{χ}\)\(^{0}_{2}\)→\(\tilde{χ}\)\(^{0}_{1}\)(h→bb/γγ/ℓ\(^{±}\)νqq). The final states considered for the search have large missing transverse momentum, an isolated electron or muon, and one of the following: either two jets identified as originating from bottom quarks, or two photons, or a second electron or muon with the same electric charge. The analysis is based on 20.3 fb\(^{-1}\) of \(\sqrt {s}\) = 8 TeV proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with the Standard Model expectations, and limits are set in the context of a simplified supersymmetric model. KW - neutralino KW - chargino KW - proton-proton collision KW - Higgs boson KW - ATLAS detector Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-150099 VL - 75 IS - 5 ER - TY - JOUR T1 - Search for dark matter in events with heavy quarks and missing transverse momentum in pp collisions with the ATLAS detector JF - European Physical Journal C: Particles and Fields N2 - This article reports on a search for dark matter pair production in association with bottom or top quarks in 20.3 fb\(^{−1}\) of pp collisions collected at \(\sqrt {s}\) = 8 TeV by the ATLAS detector at the LHC. Events with large missing transverse momentum are selected when produced in association with high-momentum jets of which one or more are identified as jets containing b-quarks. Final states with top quarks are selected by requiring a high jet multiplicity and in some cases a single lepton. The data are found to be consistent with the Standard Model expectations and limits are set on the mass scale of effective field theories that describe scalar and tensor interactions between dark matter and Standard Model particles. Limits on the dark-matter–nucleon cross-section for spin-independent and spin-dependent interactions are also provided. These limits are particularly strong for low-mass dark matter. Using a simplified model, constraints are set on the mass of dark matter and of a coloured mediator suitable to explain a possible signal of annihilating dark matter. KW - dark matter KW - proton-proton collision KW - ATLAS detector Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-150089 VL - 75 IS - 2 ER - TY - JOUR T1 - Search for a new resonance decaying to a W or Z boson and a Higgs boson in the ℓℓ/ℓν/νν+b\(\overline{b}\) final states with the ATLAS detector JF - European Physical Journal C: Particles and Fields N2 - A search for a new resonance decaying to a W or Z boson and a Higgs boson in the ℓℓ/ℓν/νν+b\(\overline{b}\) final states is performed using 20.3 fb\(^{−1}\) of pp collision data recorded at \(\sqrt {s}\) = 8 TeV with the ATLAS detector at the Large Hadron Collider. The search is conducted by examining the WH / ZH invariant mass distribution for a localized excess. No significant deviation from the Standard Model background prediction is observed. The results are interpreted in terms of constraints on the Minimal Walking Technicolor model and on a simplified approach based on a phenomenological Lagrangian of Heavy Vector Triplets. KW - Higgs boson KW - W boson KW - Z boson KW - ATLAS detector Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-150075 VL - 75 IS - 6 ER - TY - JOUR T1 - Search for W' → tb → qqbb decays in pp collisions at \(\sqrt {s}\) = 8 TeV with the ATLAS detector JF - European Physical Journal C: Particles and Fields N2 - A search for a massive W′ gauge boson decaying to a top quark and a bottom quark is performed with the ATLAS detector in pp collisions at the LHC. The dataset was taken at a centre-of-mass energy of \(\sqrt {s}\) = 8 TeV and corresponds to 20.3 fb\(^{−1}\) of integrated luminosity. This analysis is done in the hadronic decay mode of the top quark, where novel jet substructure techniques are used to identify jets from high-momentum top quarks. This allows for a search for high-mass W′ bosons in the range 1.5–3.0  TeV. b-tagging is used to identify jets originating from b-quarks. The data are consistent with Standard Model background-only expectations, and upper limits at 95 % confidence level are set on the W′ → tb cross section times branching ratio ranging from 0.16 pb to 0.33 pb for left-handed W′ bosons, and ranging from 0.10 pb to 0.21 pb for W′ bosons with purely right-handed couplings. Upper limits at 95 % confidence level are set on the W′-boson coupling to tb as a function of the W′ mass using an effective field theory approach, which is independent of details of particular models predicting a W′ boson. KW - ATLAS detector KW - proton-proton collision Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-150068 VL - 75 IS - 4 ER - TY - JOUR T1 - Observation and measurements of the production of prompt and non-prompt J/ψ mesons in association with a Z boson in pp collisions at \(\sqrt {s}\)=8 TeV with the ATLAS detector JF - European Physical Journal C: Particles and Fields N2 - The production of a Z boson in association with a J/ψ meson in proton–proton collisions probes the production mechanisms of quarkonium and heavy flavour in association with vector bosons, and allows studies of multiple parton scattering. Using 20.3fb\(^{−1}\) of data collected with the ATLAS experiment at the LHC in pp collisions at \(\sqrt {s}\) = 8 TeV, the first measurement of associated Z+J/ψ production is presented for both prompt and non-prompt J/ψ production, with both signatures having a significance in excess of 5σ. The inclusive production cross-sections for Z boson production (analysed in μ\(^{+}\)μ\(^{−}\) or e\(^{+}\)e\(^{−}\) decay modes) in association with prompt and non-prompt J/ψ(→μ\(^{+}\)μ\(^{−}\)) are measured relative to the inclusive production rate of Z bosons in the same fiducial volume to be (36.8±6.7±2.5)×10\(^{−7}\) and (65.8±9.2±4.2)×10\(^{−7}\) respectively. Normalised differential production cross-section ratios are also determined as a function of the J/ψ transverse momentum. The fraction of signal events arising from single and double parton scattering is estimated, and a lower limit of 5.3 (3.7)mb at 68 (95)% confidence level is placed on the effective cross-section regulating double parton interactions. KW - ATLAS detector KW - Z boson KW - proton-proton-collision Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-149970 VL - 75 IS - 5 ER - TY - JOUR T1 - Measurements of the W production cross sections in association with jets with the ATLAS detector JF - European Physical Journal C: Particles and Fields N2 - This paper presents cross sections for the production of a W boson in association with jets, measured in proton–proton collisions at \(\sqrt {s}\) = 7 TeV with the ATLAS experiment at the large hadron collider. With an integrated luminosity of 4.6 fb\(^{−1}\), this data set allows for an exploration of a large kinematic range, including jet production up to a transverse momentum of 1 TeV and multiplicities up to seven associated jets. The production cross sections for W bosons are measured in both the electron and muon decay channels. Differential cross sections for many observables are also presented including measurements of the jet observables such as the rapidities and the transverse momenta as well as measurements of event observables such as the scalar sums of the transverse momenta of the jets. The measurements are compared to numerous QCD predictions including next-to-leading-order perturbative calculations, resummation calculations and Monte Carlo generators. KW - ATLAS detector KW - W boson KW - proton-prton-collision Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-149925 VL - 75 IS - 2 ER - TY - JOUR T1 - Measurement of three-jet production cross-sections in pp collisions at 7 TeV centre-of-mass energy using the ATLAS detector JF - European Physical Journal C: Particles and Fields N2 - Double-differential three-jet production cross-sections are measured in proton–proton collisions at a centre-of-mass energy of \(\sqrt {s}\) = 7 TeV using the ATLAS detector at the large hadron collider. The measurements are presented as a function of the three-jet mass (m\(_{jjj}\)), in bins of the sum of the absolute rapidity separations between the three leading jets (|Y\(^{*}\)|). Invariant masses extending up to 5 TeV are reached for 8 < |Y\(^{*}\)| < 10. These measurements use a sample of data recorded using the ATLAS detector in 2011, which corresponds to an integrated luminosity of 4.51 fb\(^{-1}\). Jets are identified using the anti-k\(_{t}\) algorithm with two different jet radius parameters, R = 0.4 and R = 0.6. The dominant uncertainty in these measurements comes from the jet energy scale. Next-to-leading-order QCD calculations corrected to account for non-perturbative effects are compared to the measurements. Good agreement is found between the data and the theoretical predictions based on most of the available sets of parton distribution functions, over the full kinematic range, covering almost seven orders of magnitude in the measured cross-section values. KW - proton-proton-collisions KW - ATLAS detector Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-149918 VL - 75 IS - 5 ER - TY - JOUR T1 - Measurement of τ polarization in W→τν decays with the ATLAS detector in pp collisions at s√=7 TeV JF - The European Physical Journal C N2 - In this paper, a measurement of τ polarization in W→τν decays is presented. It is measured from the energies of the decay products in hadronic τ decays with a single final state charged particle. The data, corresponding to an integrated luminosity of 24 pb\(^{−1}\), were collected by the ATLAS experiment at the Large Hadron Collider in 2010. The measured value of the τ polarization is P\(_τ\)=−1.06±0.04 (stat)\(^{+0.05}_{−0.07}\) (syst), in agreement with the Standard Model prediction, and is consistent with a physically allowed 95 % CL interval [−1,−0.91]. Measurements of τ polarization have not previously been made at hadron colliders. KW - total systematic uncertainty KW - energy scale uncertainty KW - multijet background KW - electroweak background KW - jet energy KW - Monte Carlo methods KW - signal template KW - track momentum KW - calorimeter KW - detector track KW - transverse momentum KW - ATLAS detector KW - jet axis KW - multijet event KW - track multipilicty Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-127807 VL - 72 IS - 2062 ER -