7 research outputs found

    Measurement of differential cross sections for single diffractive dissociation in √s = 8 TeV pp collisions using the ATLAS ALFA spectrometer

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    A dedicated sample of Large Hadron Collider proton-proton collision data at centre-of-mass energy √ s = 8 TeV is used to study inclusive single diffractive dissociation, pp → Xp. The intact final-state proton is reconstructed in the ATLAS ALFA forward spectrometer, while charged particles from the dissociated system X are measured in the central detector components. The fiducial range of the measurement is −4.0 < log10 ξ < −1.6 and 0.016 < |t| < 0.43 GeV2 , where ξ is the proton fractional energy loss and t is the squared four-momentum transfer. The total cross section integrated across the fiducial range is 1.59 ± 0.13 mb. Cross sections are also measured differentially as functions of ξ, t, and ∆η, a variable that characterises the rapidity gap separating the proton and the system X. The data are consistent with an exponential t dependence, dσ/dt ∝ e Bt with slope parameter B = 7.65 ± 0.34 GeV−2 . Interpreted in the framework of triple Regge phenomenology, the ξ dependence leads to a pomeron intercept of α(0) = 1.07 ± 0.09

    Search for heavy neutral leptons in decays of W bosons produced in 13 TeV pp collisions using prompt and displaced signatures with the ATLAS detector

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    Abstract: The problems of neutrino masses, matter-antimatter asymmetry, and dark matter could be successfully addressed by postulating right-handed neutrinos with Majorana masses below the electroweak scale. In this work, leptonic decays of W bosons extracted from 32.9 fb−1 to 36.1 fb−1 of 13 TeV proton–proton collisions at the LHC are used to search for heavy neutral leptons (HNLs) that are produced through mixing with muon or electron neutrinos. The search is conducted using the ATLAS detector in both prompt and displaced leptonic decay signatures. The prompt signature requires three leptons produced at the interaction point (either μμe or eeμ) with a veto on same-flavour opposite-charge topologies. The displaced signature comprises a prompt muon from the W boson decay and the requirement of a dilepton vertex (either μμ or μe) displaced in the transverse plane by 4–300 mm from the interaction point. The search sets constraints on the HNL mixing to muon and electron neutrinos for HNL masses in the range 4.5–50 GeV

    Measurement of the top-quark mass in t t ¯ + 1-jet events collected with the ATLAS detector in pp collisions at s = 8 TeV

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    Abstract: A determination of the top-quark mass is presented using 20.2 fb−1 of 8 TeV proton-proton collision data produced by the Large Hadron Collider and collected by the ATLAS experiment. The normalised differential cross section of top-quark pair production in association with an energetic jet is measured in the lepton+jets final state and unfolded to parton and particle levels. The unfolded distribution at parton level can be described using next-to-leading-order QCD predictions in terms of either the top-quark pole mass or the running mass as defined in the (modified) minimal subtraction scheme. A comparison between the experimental distribution and the theoretical prediction allows the top-quark mass to be extracted in the two schemes. The value obtained for the pole-mass scheme is: mtpole=171.1±0.4stat±0.9syst−0.3+0.7theoGeV The extracted value in the running-mass scheme is: mtmt=162.9±0.5stat±1.0syst−1.2+2.1theoGeV. The results for the top-quark mass using the two schemes are consistent, when translated from one scheme to the other
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