TY - JOUR T1 - 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 JF - Physics Letters B N2 - 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. KW - Parton Distributions KW - Higgs boson KW - DECAY KW - Higgs boson decays KW - GAMMA Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-226147 VL - 782 ER - TY - JOUR A1 - Biedermann, Benedikt A1 - Bräuer, Stephan A1 - Denner, Ansgar A1 - Pellen, Mathieu A1 - Schumann, Steffen A1 - Thompson, Jennifer M. T1 - Automation of NLO QCD and EW corrections with SHERPA and RECOLA JF - European Physical Journal C N2 - This publication presents the combination of the one-loop matrix-element generator Recola with the multipurpose Monte Carlo program Sherpa. Since both programs are highly automated, the resulting Sherpa +Recola framework allows for the computation of – in principle – any Standard Model process at both NLO QCD and EW accuracy. To illustrate this, three representative LHC processes have been computed at NLO QCD and EW: vector-boson production in association with jets, off-shell Z-boson pair production, and the production of a top-quark pair in association with a Higgs boson. In addition to fixed-order computations, when considering QCD corrections, all functionalities of Sherpa, i.e. particle decays, QCD parton showers, hadronisation, underlying events, etc. can be used in combination with Recola. This is demonstrated by the merging and matching of one-loop QCD matrix elements for Drell–Yan production in association with jets to the parton shower. The implementation is fully automatised, thus making it a perfect tool for both experimentalists and theorists who want to use state-of-the-art predictions at NLO accuracy. KW - RECOLA KW - SHERPA KW - NLO QCD KW - EW KW - Higgs boson KW - Large Hadron Collider Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-170615 VL - 77 IS - 492 ER - TY - JOUR A1 - Denner, Ansgar A1 - Lang, Jean-Nicolas A1 - Uccirati, Sandro T1 - NLO electroweak corrections in extended Higgs sectors with RECOLA2 JF - Journal of High Energy Physics N2 - We present the computer code RECOLA2 along with the first NLO electroweak corrections to Higgs production in vector-boson fusion and updated results for Higgs strahlung in the Two-Higgs-Doublet Model and Higgs-Singlet extension of the Standard Model. A fully automated procedure for the generation of tree-level and one-loop matrix elements in general models, including renormalization, is presented. We discuss the application of the Background-Field Method to the extended models. Numerical results for NLO electroweak cross sections are presented for different renormalization schemes in the Two-Higgs-Doublet Model and the Higgs-Singlet extension of the Standard Model. Finally, we present distributions for the production of a heavy Higgs boson. KW - NLO computations KW - phenomenological models KW - Higgs boson Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-170673 VL - 7 IS - 87 ER - 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 invisible decays of the Higgs boson produced in association with a hadronically decaying vector boson in pp collisions at \(\sqrt {s}\) = TeV with the ATLAS detector JF - European Physical Journal C: Particles and Fields N2 - A search for Higgs boson decays to invisible particles is performed using 20.3 fb\(^{−1}\) of pp collision data at a centre-of-mass energy of 8 TeV recorded by the ATLAS detector at the Large Hadron Collider. The process considered is Higgs boson production in association with a vector boson (V = W or Z) that decays hadronically, resulting in events with two or more jets and large missing transverse momentum. No excess of candidates is observed in the data over the background expectation. The results are used to constrain VH production followed by H decaying to invisible particles for the Higgs boson mass range 115 < m\(_{H}\) < 300 GeV. The 95 % confidence-level observed upper limit on σ\(_{VH}\) × BR(H → inv.) varies from 1.6 pb at 115 GeV to 0.13 pb at 300 GeV. Assuming Standard Model production and including the gg → H contribution as signal, the results also lead to an observed upper limit of 78 % at 95 % confidence level on the branching ratio of Higgs bosons decays to invisible particles at a mass of 125 GeV. KW - Higgs boson KW - ATLAS detector KW - decays Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-150126 VL - 75 IS - 7 ER - TY - JOUR T1 - Measurement of the production and lepton charge asymmetry of bosons in Pb+Pb collisions at \(\sqrt {^{S}NN}\) with the ATLAS detector JF - European Physical Journal C: Particles and Fields N2 - A measurement of W boson production in lead-lead collisions at \(\sqrt {^{S}NN}\)=2.76 TeV is presented. It is based on the analysis of data collected with the ATLAS detector at the LHC in 2011 corresponding to an integrated luminosity of 0.14 nb\(^{-1}\) and 0.15 nb\(^{-1}\) in the muon and electron decay channels, respectively. The differential production yields and lepton charge asymmetry are each measured as a function of the average number of participating nucleons ⟨N\(_{part}\)⟩ and absolute pseudorapidity of the charged lepton. The results are compared to predictions based on next-to-leading-order QCD calculations. These measurements are, in principle, sensitive to possible nuclear modifications to the parton distribution functions and also provide information on scaling of W boson production in multi-nucleon systems. KW - Higgs boson KW - lead-lead collision Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-149889 VL - 75 IS - 1 ER - TY - JOUR T1 - Determination of spin and parity of the Higgs boson in the WW\(^{*}\)→eνμν decay channel with the ATLAS detector JF - European Physical Journal C: Particles and Fields N2 - Studies of the spin and parity quantum numbers of the Higgs boson in the WW\(^{*}\)→eνμν final state are presented, based on proton–proton collision data collected by the ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of 20.3 fb\(^{-1}\) at a centre-of-mass energy of \(\sqrt {s}\)=8 TeV. The Standard Model spin-parity J\(^{CP}\)=0\(^{++}\) hypothesis is compared with alternative hypotheses for both spin and CP. The case where the observed resonance is a mixture of the Standard-Model-like Higgs boson and CP-even (J\(^{CP}\)=0\(^{++}\)) or CP-odd (J\(^{CP}\)=0\(^{+-}\)) Higgs boson in scenarios beyond the Standard Model is also studied. The data are found to be consistent with the Standard Model prediction and limits are placed on alternative spin and CP hypotheses, including CP mixing in different scenarios. KW - Higgs boson KW - spin KW - parity Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-149632 VL - 75 IS - 5 ER - TY - JOUR T1 - Search for H→γγH→γγ produced in association with top quarks and constraints on the Yukawa coupling between the top quark and the Higgs boson using data taken at 7 TeV and 8 TeV with the ATLAS detector JF - Physics Letters B N2 - A search is performed for Higgs bosons produced in association with top quarks using the diphoton decay mode of the Higgs boson. Selection requirements are optimized separately for leptonic and fully hadronic final states from the top quark decays. The dataset used corresponds to an integrated luminosity of 4.5 fb\(^{−1}\) of proton–proton collisions at a center-of-mass energy of 7 TeV and 20.3 fb−120.3 fb\(^{−1}\) at 8 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. No significant excess over the background prediction is observed and upper limits are set on the \(t\overline{t}H\) production cross section. The observed exclusion upper limit at 95% confidence level is 6.7 times the predicted Standard Model cross section value. In addition, limits are set on the strength of the Yukawa coupling between the top quark and the Higgs boson, taking into account the dependence of the \(t\overline{t}H\) and tH   cross sections as well as the H→γγH→γγ branching fraction on the Yukawa coupling. Lower and upper limits at 95% confidence level are set at −1.3 and +8.0 times the Yukawa coupling strength in the Standard Model. KW - Higgs boson KW - diphoton decay KW - top quark KW - Yukawa coupling Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-136100 VL - 740 ER - TY - JOUR T1 - Constraints on the off-shell Higgs boson signal strength in the high-mass ZZ and WW final states with the ATLAS detector JF - European Physical Journal C: Particles and Fields N2 - Measurements of the ZZ and WW final states in the mass range above the 2m\(_Z\) and 2m\(_W\) thresholds provide a unique opportunity to measure the off-shell coupling strength of the Higgs boson. This paper presents constraints on the off-shell Higgs boson event yields normalised to the Standard Model prediction (signal strength) in the ZZ→4ℓ, ZZ→2ℓ2ν and WW→eνμν final states. The result is based on pp collision data collected by the ATLAS experiment at the LHC, corresponding to an integrated luminosity of 20.3 fb\(^{-1}\) at a collision energy of \(\sqrt {s}\)=8 TeV. Using the CL\(_S\) method, the observed 95 % confidence level (CL) upper limit on the off-shell signal strength is in the range 5.1–8.6, with an expected range of 6.7–11.0. In each case the range is determined by varying the unknown gg→ZZ and gg→WW background K-factor from higher-order quantum chromodynamics corrections between half and twice the value of the known signal K-factor. Assuming the relevant Higgs boson couplings are independent of the energy scale of the Higgs boson production, a combination with the on-shell measurements yields an observed (expected) 95 % CL upper limit on Γ\(_H\)/Γ\(^{SM}_{H}\) in the range 4.5–7.5 (6.5–11.2) using the same variations of the background K-factor. Assuming that the unknown gg→VV background K-factor is equal to the signal K-factor, this translates into an observed (expected) 95 % CL upper limit on the Higgs boson total width of 22.7 (33.0) MeV. KW - Higgs boson KW - coupling strength Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-149615 VL - 75 IS - 7 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 -