Accelerator Neutrinos

Abstract:

This Letter presents the first study of Higgs boson production in association with a vector boson (V=W or Z) in the fully hadronic qqbb final state using data recorded by the ATLAS detector at the LHC in proton-proton collisions at sqrt[s]=13  TeV and corresponding to an integrated luminosity of 137  fb^{-1}. The vector bosons and Higgs bosons are each reconstructed as large-radius jets and tagged using jet substructure techniques. Dedicated tagging algorithms exploiting b-tagging properties are used to identify jets consistent with Higgs bosons decaying into bb[over ¯]. Dominant backgrounds from multijet production are determined directly from the data, and a likelihood fit to the jet mass distribution of Higgs boson candidates is used to extract the number of signal events. The VH production cross section is measured inclusively and differentially in several ranges of Higgs boson transverse momentum: 250-450, 450-650, and greater than 650 GeV. The inclusive signal yield relative to the standard model expectation is observed to be μ=1.4_{-0.9}^{+1.0} and the corresponding cross section is 3.1±1.3(stat)_{-1.4}^{+1.8}(syst)  pb.

Abstract:

AbstractThis paper presents a study of $$Z \rightarrow ll\gamma $$ Z → l l γ  decays with the ATLAS detector at the Large Hadron Collider. The analysis uses a proton–proton data sample corresponding to an integrated luminosity of 20.2 fb$$^{-1}$$ - 1 collected at a centre-of-mass energy $$\sqrt{s}$$ s = 8 TeV. Integrated fiducial cross-sections together with normalised differential fiducial cross-sections, sensitive to the kinematics of final-state QED radiation, are obtained. The results are found to be in agreement with state-of-the-art predictions for final-state QED radiation. First measurements of $$Z \rightarrow ll\gamma \gamma $$ Z → l l γ γ  decays are also reported.

Abstract:

AbstractA search for the associated production of a heavy resonance with a top-quark or a top-antitop-quark pair, and decaying into a $$t{\bar{t}}$$ t t ¯ pair is presented. The search uses the data recorded by the ATLAS detector in pp collisions at $$\sqrt{s}= 13$$ s = 13  $$\text {TeV}$$ TeV at the Large Hadron Collider during the years 2015–2018, corresponding to an integrated luminosity of 139 $$\text {fb}^{-1}$$ fb - 1 . Events containing exactly one electron or muon are selected. The two hadronically decaying top quarks from the resonance decay are reconstructed using jets clustered with a large radius parameter of $$R=1$$ R = 1 . The invariant mass spectrum of the two top quark candidates is used to search for a resonance signal in the range of 1.0 $$\text {TeV}$$ TeV to 3.2 $$\text {TeV}$$ TeV . The presence of a signal is examined using an approach with minimal model dependence followed by a model-dependent interpretation. No significant excess is observed over the background expectation. Upper limits on the production cross section times branching ratio at 95% confidence level are provided for a heavy $$Z^\prime $$ Z ′ boson based on a simplified model, for $$Z^\prime $$ Z ′ mass between 1.0 $$\text {TeV}$$ TeV and 3.0 $$\text {TeV}$$ TeV . The observed (expected) limits range from 21 (14) fb to 119 (86) fb depending on the choice of model parameters.