145 research outputs found

    Measurement of the production cross section for W-bosons in association with jets in pp collisions at s=7 TeV with the ATLAS detector

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    This Letter reports on a first measurement of the inclusive W + jets cross section in proton-proton collisions at a centre-of-mass energy of 7 TeV at the LHC, with the ATLAS detector. Cross sections, in both the electron and muon decay modes of the W-boson, are presented as a function of jet multiplicity and of the transverse momentum of the leading and next-to-leading jets in the event. Measurements are also presented of the ratio of cross sections sigma (W + >= n)/sigma(W + >= n - 1) for inclusive jet multiplicities n = 1-4. The results, based on an integrated luminosity of 1.3 pb(-1), have been corrected for all known detector effects and are quoted in a limited and well-defined range of jet and lepton kinematics. The measured cross sections are compared to particle-level predictions based on perturbative QCD. Next-to-leading order calculations, studied here for n <= 2, are found in good agreement with the data. Leading-order multiparton event generators, normalized to the NNLO total cross section, describe the data well for all measured jet multiplicitie

    Measurement of the dependence of transverse energy production at large pseudorapidity on the hard-scattering kinematics of proton-proton collisions at √s=2.76 TeV with ATLAS

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    The relationship between jet production in the central region and the underlying-event activity in a pseudorapidity-separated region is studied in 4.0 pb-1 of s=2.76 TeV pp collision data recorded with the ATLAS detector at the LHC. The underlying event is characterised through measurements of the average value of the sum of the transverse energy at large pseudorapidity downstream of one of the protons, which are reported here as a function of hard-scattering kinematic variables. The hard scattering is characterised by the average transverse momentum and pseudorapidity of the two highest transverse momentum jets in the event. The dijet kinematics are used to estimate, on an event-by-event basis, the scaled longitudinal momenta of the hard-scattered partons in the target and projectile beam-protons moving toward and away from the region measuring transverse energy, respectively. Transverse energy production at large pseudorapidity is observed to decrease with a linear dependence on the longitudinal momentum fraction in the target proton and to depend only weakly on that in the projectile proton. The results are compared to the predictions of various Monte Carlo event generators, which qualitatively reproduce the trends observed in data but generally underpredict the overall level of transverse energy at forward pseudorapidity

    Search for the Exclusive W Boson Hadronic Decays W±→π±γ , W±→K±γ and W±→ρ±γ with the ATLAS Detector

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    Measurement of the H → γ γ and H → ZZ∗ → 4 cross-sections in pp collisions at √s = 13.6 TeV with the ATLAS detector

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    The inclusive Higgs boson production cross section is measured in the di-photon and the Z Z∗ → 4 decay channels using 31.4 and 29.0 fb−1 of pp collision data respectively, collected with the ATLAS detector at a centre of-mass energy of √s = 13.6 TeV. To reduce the model dependence, the measurement in each channel is restricted to a particle-level phase space that closely matches the chan nel’s detector-level kinematic selection, and it is corrected for detector effects. These measured fiducial cross-sections are σfid,γ γ = 76+14 −13 fb, and σfid,4 = 2.80 ± 0.74 fb, in agreement with the corresponding Standard Model predic tions of 67.6±3.7 fb and 3.67±0.19 fb. Assuming Standard Model acceptances and branching fractions for the two chan nels, the fiducial measurements are extrapolated to the full phase space yielding total cross-sections of σ (pp → H) = 67+12 −11 pb and 46±12 pb at 13.6 TeV from the di-photon and Z Z∗ → 4 measurements respectively. The two measure ments are combined into a total cross-section measurement of σ (pp → H) = 58.2±8.7 pb, to be compared with the Stan dard Model prediction of σ (pp → H)SM = 59.9 ± 2.6 p

    Electron and photon energy calibration with the ATLAS detector using LHC Run 2 data

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    This paper presents the electron and photon energy calibration obtained with the ATLAS detector using 140 fb−1 of LHC proton-proton collision data recorded at root(s) = 13 TeV between 2015 and 2018. Methods for the measurement of electron and photon energies are outlined, along with the current knowledge of the passive material in front of the ATLAS electromagnetic calorimeter. The energy calibration steps are discussed in detail, with emphasis on the improvements introduced in this paper. The absolute energy scale is set using a large sample of Z-boson decays into electron-positron pairs, and its residual dependence on the electron energy is used for the first time to further constrain systematic uncertainties. The achieved calibration uncertainties are typically 0.05% for electrons from resonant Z-boson decays, 0.4% at ET tilde 10 GeV, and 0.3% at ET tilde 1 TeV; for photons at ET tilde 60 GeV, they are 0.2% on average. This is more than twice as precise as the previous calibration. The new energy calibration is validated using J/psi -&gt; ee and radiative Z-boson decays

    Statistical Combination of ATLAS Run 2 Searches for Charginos and Neutralinos at the LHC

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    Statistical combinations of searches for charginos and neutralinos using various decay channels are performed using 139 fb^{-1} of pp collision data at sqrt[s]=13 TeV with the ATLAS detector at the Large Hadron Collider. Searches targeting pure-wino chargino pair production, pure-wino chargino-neutralino production, or Higgsino production decaying via standard model W, Z, or h bosons are combined to extend the mass reach to the produced supersymmetric particles by 30-100&nbsp;GeV. The depth of the sensitivity of the original searches is also improved by the combinations, lowering the 95% C.L. cross-section upper limits by 15%-40%

    Search for light long-lived neutral particles from Higgs boson decays via vector-boson-fusion production from pp collisions at s=13\sqrt{s}=13 TeV with the ATLAS detector

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    Measurement of ZZ production cross-sections in the four-lepton final state in pp collisions at √s = 13.6 TeV with the ATLAS experiment

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    A search for top-squark pair production, in final states containing a top quark, a charm quark and missing transverse momentum, using the 139 fb−1 of pp collision data collected by the ATLAS detector

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    Measurement of t-channel single-top-quark production in pp collisions at √s = 5.02 TeV with the ATLAS detector

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