L. Zwalinski

Topological cell clustering in the ATLAS calorimeters and its performance in LHC Run 1

The reconstruction of the signal from hadrons and jets emerging from the proton–proton collisions at the Large Hadron Collider (LHC) and entering the ATLAS calorimeters is based on a three-dimensional topological clustering of individual calorimeter cell signals. The cluster formation follows cell signal-significance patterns generated by electromagnetic and hadronic showers. In this, the clustering algorithm implicitly performs a topological noise suppression by removing cells with insignificant signals which are not in close proximity to cells with significant signals. The resulting topological cell clusters have shape and location information, which is exploited to apply a local energy calibration and corrections depending on the nature of the cluster. Topological cell clustering is established as a well-performing calorimeter signal definition for jet and missing transverse momentum reconstruction in ATLAS.

Evidence for the associated production of the Higgs boson and a top quark pair with the ATLAS detector

A search for the associated production of the Higgs boson with a top quark pair (tt̄H) is reported. The search is performed in multilepton final states using a dataset corresponding to an integrated luminosity of 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at a center-of-mass energy √ s = 13 TeV at the Large Hadron Collider. Higgs boson decays toWW∗, ττ, and Z Z∗ are targeted. Seven final states, categorized by the number and flavor of charged-lepton candidates, are examined for the presence of the Standard Model Higgs boson with a mass of 125 GeV and a pair of top quarks. An excess of events over the expected background from Standard Model processes is found with an observed significance of 4.1 standard deviations, compared to an expectation of 2.8 standard deviations. The best fit for the tt̄H production cross section is σ(tt̄H) = 790+230 −210 fb, in agreement with the Standard Model prediction of 507+35 −50 fb. The combination of this result with other tt̄H searches from the ATLAS experiment using the Higgs boson decay modes to bb̄, γγ and Z Z∗ → 4`, has an observed significance of 4.2 standard deviations, compared to an expectation of 3.8 standard deviations. This provides evidence for the tt̄H production mode.

Search for long-lived, massive particles in events with displaced vertices and missing transverse momentum in s =13 TeV pp collisions with the ATLAS detector

A search for long-lived, massive particles predicted by many theories beyond the Standard Model is presented. The search targets final states with large missing transverse momentum and at least one high-mass displaced vertex with five or more tracks, and uses 32.8 fb−1 of √ s = 13 TeV pp collision data collected by the ATLAS detector at the LHC. The observed yield is consistent with the expected background. The results are used to extract 95% CL exclusion limits on the production of long-lived gluinos with masses up to 2.37 TeV and lifetimes of O(10−2)–O(10) ns in a simplified model inspired by Split Supersymmetry.

Search for the Dimuon Decay of the Higgs Boson in pp Collisions at s =13 TeV with the ATLAS Detector

A search for the dimuon decay of the Higgs boson has been performed using data corresponding to an integrated luminosity of 36.1 fb−1 collected with the ATLAS detector in pp collisions at √ s =13 TeV at the LHC. No significant excess is observed above the background expectation. The observed (expected) upper limit on the cross-section times the branching ratio is 3.0 (3.1) times the Standard Model prediction at the 95% confidence level for a Higgs boson mass of 125 GeV. When combined with the pp collisions data at √ s =7 TeV and √ s =8 TeV, the observed (expected) upper limit is 2.8 (2.9) times the Standard Model prediction.A search for the dimuon decay of the Higgs boson was performed using data corresponding to an integrated luminosity of 36.1u2009u2009fb^{-1} collected with the ATLAS detector in pp collisions at sqrt[s]=13u2009u2009TeV at the Large Hadron Collider. No significant excess is observed above the expected background. The observed (expected) upper limit on the cross section times branching ratio is 3.0 (3.1) times the Standard Model prediction at the 95%xa0confidence level for a Higgs boson mass of 125xa0GeV. When combined with the pp collision data at sqrt[s]=7u2009u2009TeV and sqrt[s]=8u2009u2009TeV, the observed (expected) upper limit is 2.8 (2.9) times the Standard Model prediction.

Measurement of the differential cross-sections of prompt and non-prompt production of J / ψ and ψ (2S) in pp collisions at √s = 7 and 8 TeV with the ATLAS detector

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Measurement of long-range multiparticle azimuthal correlations with the subevent cumulant method in pp and p plus Pb collisions with the ATLAS detector at the CERN Large Hadron Collider

J/psi

Evidence for the H → bb¯ decay with the ATLAS detector

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