A bstract A search for the exclusive decays of the Higgs and Z bosons to a ϕ or ρ meson and a photon is performed with a pp collision data sample corresponding to an integrated luminosity of up to 35 . 6 fb −1 collected at $$ \sqrt{s}=13 $$ s = 13 TeV with the ATLAS detector at the CERN Large Hadron Collider. These decays have been suggested as a probe of the Higgs boson couplings to light quarks. No significant excess of events is observed above the background, as expected from the Standard Model. Upper limits at 95% confidence level were obtained on the branching fractions of the Higgs boson decays to ϕ γ and ρ γ of 4 . 8 × 10 −4 and 8 . 8 × 10 −4 , respectively. The corresponding 95% confidence level upper limits for the Z boson decays are 0 . 9 × 10 −6 and 25 × 10 −6 for ϕ γ and ρ γ, respectively.

The production cross-sections for W +/- and Z bosons are measured using ATLAS data corresponding to an integrated luminosity of 4.0 pb-1 collected at a centre-ofmass energy v s = 2.76 TeV. The deca ...

This change does not have any impact on the measured helicity fractions, but it changes the obtained limits on the anomalous couplings.

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 √(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 300-5000GeV 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.

The shared HPC cluster NEMO at the University of Freiburg has been made available to local ATLAS users through the provisioning of virtual machines incorporating the ATLAS software environment analogously to a WLCG center. This concept allows to run both data analysis and production on the HPC host system which is connected to the existing Tier2/Tier3 infrastructure. Schedulers of the two clusters were integrated in a dynamic, on-demand way. An automatically generated, fully functional virtual machine image provides access to the local user environment. The performance in the virtualized environment is evaluated for typical High-Energy Physics applications.

Abstract A search for supersymmetry involving the pair production of gluinos decaying via third-generation squarks into the lightest neutralino $$ \left({\tilde{\chi}}_1^0\right) $$ χ ˜ 1 0 is reported. It uses LHC proton-proton collision data at a centre-of-mass energy $$ \sqrt{s}=13 $$ s = 13 TeV with an integrated luminosity of 36.1 fb−1 collected with the ATLAS detector in 2015 and 2016. The search is performed in events containing large missing transverse momentum and several energetic jets, at least three of which must be identified as originating from b-quarks. To increase the sensitivity, the sample is divided into subsamples based on the presence or absence of electrons or muons. No excess is found above the predicted background. For $$ {\tilde{\chi}}_1^0 $$ χ ˜ 1 0 masses below approximately 300 GeV, gluino masses of less than 1.97 (1.92) TeV are excluded at 95% confidence level in simplified models involving the pair production of gluinos that decay via top (bottom) squarks. An interpretation of the limits in terms of the branching ratios of the gluinos into third-generation squarks is also provided. These results improve upon the exclusion limits obtained with the 3.2 fb−1 of data collected in 2015.

This paper presents a search for direct electroweak gaugino or gluino pair production with a chargino nearly mass-degenerate with a stable neutralino. It is based on an integrated luminosity of 36.1 $\mathrm{fb}^{-1}$ of $pp$ collisions at $\sqrt{s} = 13$ TeV collected by the ATLAS experiment at the LHC. The final state of interest is a disappearing track accompanied by at least one jet with high transverse momentum from initial-state radiation or by four jets from the gluino decay chain. The use of short track segments reconstructed from the innermost tracking layers significantly improves the sensitivity to short chargino lifetimes. The results are found to be consistent with Standard Model predictions. Exclusion limits are set at 95% confidence level on the mass of charginos and gluinos for different chargino lifetimes. For a pure wino with a lifetime of about 0.2 ns, chargino masses up to 460 GeV are excluded. For the strong production channel, gluino masses up to 1.65 TeV are excluded assuming a chargino mass of 460 GeV and lifetime of 0.2 ns.

Abstract Measurements of longitudinal flow correlations are presented for charged particles in the pseudorapidity range $$|\eta |<2.4$$ |η|<2.4 using 7 and 470 $$\upmu \hbox {b}^{-1}$$ μb-1 of Pb+Pb collisions at $$\sqrt{s_{\text {NN}}}=2.76$$ sNN=2.76 and 5.02 TeV, respectively, recorded by the ATLAS detector at the LHC. It is found that the correlation between the harmonic flow coefficients $$v_n$$ vn measured in two separated $$\eta $$ η intervals does not factorise into the product of single-particle coefficients, and this breaking of factorisation, or flow decorrelation, increases linearly with the $$\eta $$ η separation between the intervals. The flow decorrelation is stronger at 2.76 TeV than at 5.02 TeV. Higher-order moments of the correlations are also measured, and the corresponding linear coefficients for the $$k{\text {th}}$$ kth -moment of the $$v_n$$ vn are found to be proportional to k for $$v_3$$ v3 , but not for $$v_2$$ v2 . The decorrelation effect is separated into contributions from the magnitude of $$v_n$$ vn and the event-plane orientation, each as a function of $$\eta $$ η . These two contributions are found to be comparable. The longitudinal flow correlations are also measured between $$v_n$$ vn of different order in n. The decorrelations of $$v_2$$ v2 and $$v_3$$ v3 are found to be independent of each other, while the decorrelations of $$v_4$$ v4 and $$v_5$$ v5 are found to be driven by the nonlinear contribution from $$v_2^2$$ v22 and $$v_2v_3$$ v2v3 , respectively.

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)

Searches for the exclusive decays of the Higgs and Z bosons into a J/ψ, ψ(2S), or ϒ(nS) (n=1,2,3) meson and a photon are performed with a pp collision data sample corresponding to an integrated luminosity of 36.1fb−1 collected at s=13TeV with the ATLAS detector at the CERN Large Hadron Collider. No significant excess of events is observed above the expected backgrounds, and 95% confidence-level upper limits on the branching fractions of the Higgs boson decays to J/ψγ, ψ(2S)γ, and ϒ(nS)γ of 3.5×10−4, 2.0×10−3, and (4.9,5.9,5.7)×10−4, respectively, are obtained assuming Standard Model production. The corresponding 95% confidence-level upper limits for the branching fractions of the Z boson decays are 2.3×10−6, 4.5×10−6 and (2.8,1.7,4.8)×10−6, respectively.

Abstract Inclusive jet and dijet cross-sections are measured in proton-proton collisions at a centre-of-mass energy of 13 TeV. The measurement uses a dataset with an integrated luminosity of 3.2 fb−1 recorded in 2015 with the ATLAS detector at the Large Hadron Collider. Jets are identified using the anti-k t algorithm with a radius parameter value of R = 0.4. The inclusive jet cross-sections are measured double-differentially as a function of the jet transverse momentum, covering the range from 100 GeV to 3.5 TeV, and the absolute jet rapidity up to |y| = 3. The double-differential dijet production cross-sections are presented as a function of the dijet mass, covering the range from 300 GeV to 9 TeV, and the half absolute rapidity separation between the two leading jets within |y| < 3, y ∗, up to y ∗ = 3. Next-to-leading-order, and next-to-next-to-leading-order for the inclusive jet measurement, perturbative QCD calculations corrected for non-perturbative and electroweak effects are compared to the measured cross-sections.

Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B; Abhayasinghe, DK; Abidi, S.H.; Abouzeid, Ossama Sherif Alexander; Abraham, NL; Abramowicz, H.; Abreu, H.; Abulaiti, Y.; Acharya, B.S.; Adachi, Shin-ichi; Adamczyk, L.; Adelman, J.; Adersberger, M.; Adiguzel, A.; Adye, T.; Affolder, A. A.; Afik, Y. ; Besjes, Geert-Jan; Bajic, Milena; Alonso Diaz, Alejandro; de Almeida Dias, Flavia; Dam, Mogens; Hansen, Peter Henrik; Hansen, Jørn Dines; Hansen, Jørgen Beck; Galster, Gorm Aske Gram Krohn; Monk, James William; Petersen, Troels Christian; Thiele, Fabian Alexander Jürgen; Xella, Stefania; Stark, Simon Holm; Wiglesworth, Graig

Abstract Charged Higgs bosons produced either in top-quark decays or in association with a top-quark, subsequently decaying via H ± → τ ± ν τ , are searched for in 36.1 fb−1 of proton-proton collision data at $$ \sqrt{s}=13 $$ s = 13 TeV recorded with the ATLAS detector. Depending on whether the top-quark produced together with H ± decays hadronically or leptonically, the search targets τ+jets and τ+lepton final states, in both cases with a hadronically decaying τ-lepton. No evidence of a charged Higgs boson is found. For the mass range of $$ {m}_{H^{\pm }} $$ m H ± = 90–2000 GeV, upper limits at the 95% confidence level are set on the production cross-section of the charged Higgs boson times the branching fraction $$ \mathrm{\mathcal{B}}\left({H}^{\pm}\to {\tau}^{\pm }{\nu}_{\tau}\right) $$ ℬ H ± → τ ± ν τ in the range 4.2–0.0025 pb. In the mass range 90–160 GeV, assuming the Standard Model cross-section for $$ t\overline{t} $$ t t ¯ production, this corresponds to upper limits between 0.25% and 0.031% for the branching fraction $$ \mathrm{\mathcal{B}}\left(t\to b{H}^{\pm}\right)\times \mathrm{\mathcal{B}}\left({H}^{\pm}\to {\tau}^{\pm }{\nu}_{\tau}\right) $$ ℬ t → b H ± × ℬ H ± → τ ± ν τ .

A search for the supersymmetric partners of quarks and gluons (squarks and gluinos) in final states containing hadronic jets and missing transverse momentum, but no electrons or muons, is presented. The data used in this search were recorded in 2015 and 2016 by the ATLAS experiment in ffiffiffi s p ¼ TeV proton-proton collisions at the Large Hadron Collider, corresponding to an integrated luminosity of 36 . 1 fb − 1 . The results are interpreted in the context of various models where squarks and gluinos are pair produced and the neutralino is the lightest supersymmetric particle. An exclusion limit at the 95% confidence level on the mass of the gluino is set at 2.03 TeV for a simplified model incorporating only a gluino and the lightest neutralino, assuming the lightest neutralino is massless. For a simplified model involving the strong production of mass-degenerate first- and second-generation squarks, squark masses below 1.55 TeVare excluded if the lightest neutralino is massless. These limits substantially extend the region of supersymmetric parameter space previously excluded by searches with the ATLAS detector. and the dotted lines are obtained by varying the signal cross section by the renormalization and factorization scale and PDF uncertainties. Results are compared with the observed limits obtained by the previous ATLAS searches with jets, missing transverse momentum, and no leptons [11].

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.

A bstract A measurement of b -hadron pair production is presented, based on a data set corresponding to an integrated luminosity of 11.4 fb −1 of proton-proton collisions recorded at $$ \sqrt{s}=8 $$ s = 8 TeV with the ATLAS detector at the LHC. Events are selected in which a b -hadron is reconstructed in a decay channel containing J/ψ → μμ , and a second b -hadron is reconstructed in a decay channel containing a muon. Results are presented in a fiducial volume defined by kinematic requirements on three muons based on those used in the analysis. The fiducial cross section is measured to be 17.7 ± 0.1(stat.) ± 2.0(syst.) nb. A number of normalised differential cross sections are also measured, and compared to predictions from the P ythia 8, H erwig ++, M ad G raph 5_ a MC@NLO+P ythia 8 and S herpa event generators, providing new constraints on heavy flavour production.