Showing papers by "Alastair Dewhurst published in 2020"
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23 Feb 2020
TL;DR: The ATLAS detector as installed in its experimental cavern at point 1 at CERN is described in this paper, where a brief overview of the expected performance of the detector when the Large Hadron Collider begins operation is also presented.
Abstract: The ATLAS detector as installed in its experimental cavern at point 1 at CERN is described in this paper. A brief overview of the expected performance of the detector when the Large Hadron Collider begins operation is also presented.
3,111 citations
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TL;DR: Combined measurements of Higgs boson production cross sections and branching fractions arc are presented in this paper, based on the analyses of the Higgs particle decay modes H -> gamma gamma, ZZ...
Abstract: Combined measurements of Higgs boson production cross sections and branching fractions arc presented. The combination is based on the analyses of the Higgs boson decay modes H -> gamma gamma, ZZ ...
505 citations
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TL;DR: In this article, a search for the electroweak production of charginos and sleptons decaying into final states with two electrons or muons is presented, based on 139.fb$^{-1}$ of proton-proton collisions recorded by the ATLAS detector at the Large Hadron Collider at
Abstract: A search for the electroweak production of charginos and sleptons decaying into final states with two electrons or muons is presented. The analysis is based on 139 fb$^{-1}$ of proton–proton collisions recorded by the ATLAS detector at the Large Hadron Collider at $\sqrt{s}=13$ $\text {TeV}$. Three R-parity-conserving scenarios where the lightest neutralino is the lightest supersymmetric particle are considered: the production of chargino pairs with decays via either W bosons or sleptons, and the direct production of slepton pairs. The analysis is optimised for the first of these scenarios, but the results are also interpreted in the others. No significant deviations from the Standard Model expectations are observed and limits at 95% confidence level are set on the masses of relevant supersymmetric particles in each of the scenarios. For a massless lightest neutralino, masses up to 420 $\text {Ge}\text {V}$ are excluded for the production of the lightest-chargino pairs assuming W-boson-mediated decays and up to 1 $\text {TeV}$ for slepton-mediated decays, whereas for slepton-pair production masses up to 700 $\text {Ge}\text {V}$ are excluded assuming three generations of mass-degenerate sleptons.
272 citations
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TL;DR: In this paper, the trigger algorithms and selection were optimized to control the rates while retaining a high efficiency for physics analyses at the ATLAS experiment to cope with a fourfold increase of peak LHC luminosity from 2015 to 2018 (Run 2), and a similar increase in the number of interactions per beam-crossing to about 60.
Abstract: Electron and photon triggers covering transverse energies from 5 GeV to several TeV are essential for the ATLAS experiment to record signals for a wide variety of physics: from Standard Model processes to searches for new phenomena in both proton–proton and heavy-ion collisions. To cope with a fourfold increase of peak LHC luminosity from 2015 to 2018 (Run 2), to 2.1×1034cm-2s-1, and a similar increase in the number of interactions per beam-crossing to about 60, trigger algorithms and selections were optimised to control the rates while retaining a high efficiency for physics analyses. For proton–proton collisions, the single-electron trigger efficiency relative to a single-electron offline selection is at least 75% for an offline electron of 31 GeV, and rises to 96% at 60 GeV; the trigger efficiency of a 25 GeV leg of the primary diphoton trigger relative to a tight offline photon selection is more than 96% for an offline photon of 30 GeV. For heavy-ion collisions, the primary electron and photon trigger efficiencies relative to the corresponding standard offline selections are at least 84% and 95%, respectively, at 5 GeV above the corresponding trigger threshold.
180 citations
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TL;DR: In this article, a search for the direct production of the supersymmetric partners of staus (staus) in final states with two hadronically decaying leptons is presented.
Abstract: A search for the direct production of the supersymmetric partners of
τ
-leptons (staus) in final states with two hadronically decaying
τ
-leptons is presented. The analysis uses a dataset of
p
p
collisions corresponding to an integrated luminosity of
139
fb
−
1
, recorded with the ATLAS detector at the Large Hadron Collider at a center-of-mass energy of 13 TeV. No significant deviation from the expected Standard Model background is observed. Limits are derived in scenarios of direct production of stau pairs with each stau decaying into the stable lightest neutralino and one
τ
-lepton in simplified models where the two stau mass eigenstates are degenerate. Stau masses from 120 GeV to 390 GeV are excluded at 95% confidence level for a massless lightest neutralino.
69 citations
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TL;DR: In this article, a search for heavy neutral Higgs bosons produced in association with one or two b-quarks and decaying to bquark pairs is presented using 27.8 fb(-1) of root s=13 TeV proton-proton collision data.
Abstract: A search for heavy neutral Higgs bosons produced in association with one or two b-quarks and decaying to b-quark pairs is presented using 27.8 fb(-1) of root s=13 TeV proton-proton collision data r ...
53 citations
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TL;DR: In this article, a search for supersymmetric partners of gluons and quarks is presented, involving signatures with jets and either two isolated leptons (electrons or muons) with the same electric charge.
Abstract: A search for supersymmetric partners of gluons and quarks is presented, involving signatures with jets and either two isolated leptons (electrons or muons) with the same electric charge, or at leas ...
45 citations
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TL;DR: In this paper, a search for long-lived particles decaying into an oppositely charged lepton pair, mu mu, ee, or e mu, is presented using 32.8 fb(-1) of pp collision data collected at root s = 13 TeV by the ATLAS.
44 citations
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TL;DR: In this paper, a measurement of observables sensitive to spin correlations in tt¯ production is presented, using 36.1 fb - 1 of pp collision data at s=13 TeV recorded with the ATLAS detector at the Large Hadron Collider.
Abstract: A measurement of observables sensitive to spin correlations in tt¯ production is presented, using 36.1 fb - 1 of pp collision data at s=13 TeV recorded with the ATLAS detector at the Large Hadron Collider. Differential cross-sections are measured in events with exactly one electron and one muon with opposite-sign electric charge as a function of the azimuthal opening angle and the absolute difference in pseudorapidity between the electron and muon candidates in the laboratory frame. The azimuthal opening angle is also measured as a function of the invariant mass of the tt¯ system. The measured differential cross-sections are compared to predictions by several NLO Monte Carlo generators and fixed-order calculations. The observed degree of spin correlation is somewhat higher than predicted by the generators used. The data are consistent with the prediction of one of the fixed-order calculations at NLO, but agree less well with higher-order predictions. Using these leptonic observables, a search is performed for pair production of supersymmetric top squarks decaying into Standard Model top quarks and light neutralinos. Top squark masses between 170 and 230 GeV are largely excluded at the 95% confidence level for kinematically allowed values of the neutralino mass.
39 citations
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TL;DR: A search for Higgs boson pair production via vector-boson fusion (VBF) in the bbbb final state is carried out with the ATLAS experiment using 126 fb(-1) of proton-proton collision data delivered a...
Abstract: A search for Higgs boson pair production via vector-boson fusion (VBF) in the bbbb final state is carried out with the ATLAS experiment using 126 fb(-1) of proton- proton collision data delivered a ...
36 citations
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TL;DR: Searches for the Higgs boson were performed using data corresponding to an integrated luminosity of 139 fb(-1) collected with the ATLAS detector in pp collisions as discussed by the authors.
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TL;DR: A search for magnetic monopoles and high-electric-charge objects is presented using 34.4 fb^{-1} of 13 TeV pp collision data collected by the ATLAS detector at the LHC during 2015 and 2016, improving by approximately a factor of 5 the constraints on the direct production of magnetic monopole carrying one or two Dirac magnetic charges.
Abstract: A search for magnetic monopoles and high-electric-charge objects is presented using 34.4 fb^{-1} of 13 TeV pp collision data collected by the ATLAS detector at the LHC during 2015 and 2016. The considered signature is based upon high ionization in the transition radiation tracker of the inner detector associated with a pencil-shape energy deposit in the electromagnetic calorimeter. The data were collected by a dedicated trigger based on the tracker high-threshold hit capability. The results are interpreted in models of Drell-Yan pair production of stable particles with two spin hypotheses (0 and 1/2) and masses ranging from 200 to 4000 GeV. The search improves by approximately a factor of 5 the constraints on the direct production of magnetic monopoles carrying one or two Dirac magnetic charges and stable objects with electric charge in the range 20≤|z|≤60 and extends the charge range to 60<|z|≤100.
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TL;DR: In this article, a search for long-lived particles decaying into hadrons and at least one muon is presented, where the analysis selects events that pass a muon or missing transverse-momentum trigger and contain a displaced muon track and a displaced vertex.
Abstract: A search for long-lived particles decaying into hadrons and at least one muon is presented. The analysis selects events that pass a muon or missing-transverse-momentum trigger and contain a displaced muon track and a displaced vertex. The analyzed dataset of proton-proton collisions at s=13 TeV was collected with the ATLAS detector and corresponds to 136 fb-1. The search employs dedicated reconstruction techniques that significantly increase the sensitivity to long-lived particle decays that occur in the ATLAS inner detector. Background estimates for Standard Model processes and instrumental effects are extracted from data. The observed event yields are compatible with those expected from background processes. The results are presented as limits at 95% confidence level on model-independent cross sections for processes beyond the Standard Model, and interpreted as exclusion limits in scenarios with pair production of long-lived top squarks that decay via a small R-parity-violating coupling into a quark and a muon. Top squarks with masses up to 1.7 TeV are excluded for a lifetime of 0.1 ns, and masses below 1.3 TeV are excluded for lifetimes between 0.01 ns and 30 ns.
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TL;DR: In this article, multi-particle azimuthal cumulants are measured as a function of centrality and transverse momentum using 470 mu b(-1) of Pb+Pb collisions at root s(NN) = 5.02TeV with the ATLAS detector at the LHC.
Abstract: Multi-particle azimuthal cumulants are measured as a function of centrality and transverse momentum using 470 mu b(-1) of Pb+Pb collisions at root s(NN) = 5.02TeV with the ATLAS detector at the LHC ...
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TL;DR: A double-differential cross-section measurement of the Lund jet plane is presented using proton-proton collision data collected with the ATLAS detector using jets with transverse momentum above 675 GeV.
Abstract: The prevalence of hadronic jets at the LHC requires that a deep understanding of jet formation and structure is achieved in order to reach the highest levels of experimental and theoretical precision. There have been many measurements of jet substructure at the LHC and previous colliders, but the targeted observables mix physical effects from various origins. Based on a recent proposal to factorize physical effects, this Letter presents a double-differential cross-section measurement of the Lund jet plane using 139 fb^{-1} of sqrt[s]=13 TeV proton-proton collision data collected with the ATLAS detector using jets with transverse momentum above 675 GeV. The measurement uses charged particles to achieve a fine angular resolution and is corrected for acceptance and detector effects. Several parton shower Monte Carlo models are compared with the data. No single model is found to be in agreement with the measured data across the entire plane.
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TL;DR: In this paper, a measurement of the production of a prompt J/psi meson in association with a W-+/- boson with W−/- -> mu nu and J−psi -> mu(+)mu(-) is presented.
Abstract: A measurement of the production of a prompt J/psi meson in association with a W-+/- boson with W-+/- -> mu nu and J/psi -> mu(+)mu(-) is presented for J/psi transverse momenta in the range 8. ...
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TL;DR: The elliptic flow of muons from the decay of charm and bottom hadrons is measured in pp collisions at sqrt[s]=13 TeV using a data sample with an integrated luminosity of 150’ pb^{-1} recorded by the ATLAS detector at the LHC.
Abstract: The elliptic flow of muons from the decay of charm and bottom hadrons is measured in pp collisions at sqrt[s]=13 TeV using a data sample with an integrated luminosity of 150 pb^{-1} recorded by the ATLAS detector at the LHC. The muons from heavy-flavor decay are separated from light-hadron decay muons using momentum imbalance between the tracking and muon spectrometers. The heavy-flavor decay muons are further separated into those from charm decay and those from bottom decay using the distance-of-closest-approach to the collision vertex. The measurement is performed for muons in the transverse momentum range 4-7 GeV and pseudorapidity range |η|<2.4. A significant nonzero elliptic anisotropy coefficient v_{2} is observed for muons from charm decays, while the v_{2} value for muons from bottom decays is consistent with zero within uncertainties.
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TL;DR: In this article, the authors measured the jet energy scale, jet energy resolution, and their systematic uncertainties for jets reconstructed with the ATLAS detector in 2012 using proton-proton data produced at a centre-of-mass energy of 8 TeV with an integrated luminosity of 20fb−1.
Abstract: The jet energy scale, jet energy resolution, and their systematic uncertainties are measured for jets reconstructed with the ATLAS detector in 2012 using proton–proton data produced at a centre-of-mass energy of 8 TeV with an integrated luminosity of 20fb−1. Jets are reconstructed from clusters of energy depositions in the ATLAS calorimeters using the anti-kt algorithm. A jet calibration scheme is applied in multiple steps, each addressing specific effects including mitigation of contributions from additional proton–proton collisions, loss of energy in dead material, calorimeter non-compensation, angular biases and other global jet effects. The final calibration step uses several in situ techniques and corrects for residual effects not captured by the initial calibration. These analyses measure both the jet energy scale and resolution by exploiting the transverse momentum balance in γ + jet, Z + jet, dijet, and multijet events. A statistical combination of these measurements is performed. In the central detector region, the derived calibration has a precision better than 1% for jets with transverse momentum 150GeV
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TL;DR: In this article, the results from the measurement by ATLAS of long-range (|Delta eta|>2) dihadron angular correlations in root s=8 and 13 TeV pp collisions containing a Z boson are presented.
Abstract: Results are presented from the measurement by ATLAS of long-range (|Delta eta|>2) dihadron angular correlations in root s=8 and 13 TeV pp collisions containing a Z boson. The analysis is perform ...
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TL;DR: A mistake was identified for the paper [1] in the treatment of the radion cross-sections, which resulted in multiple changes.
Abstract: Author(s): Aad, G; Abbott, B; Abbott, DC; Abdinov, O; Abed Abud, A; Abeling, K; Abhayasinghe, DK; Abidi, SH; AbouZeid, OS; Abraham, NL; Abramowicz, H; Abreu, H; Abulaiti, Y; Acharya, BS; Achkar, B; Adachi, S; Adam, L; Adam Bourdarios, C; Adamczyk, L; Adamek, L; Adelman, J; Adersberger, M; Adiguzel, A; Adorni, S; Adye, T; Affolder, AA; Afik, Y; Agapopoulou, C; Agaras, MN; Aggarwal, A; Agheorghiesei, C; Aguilar-Saavedra, JA; Ahmadov, F; Ahmed, WS; Ai, X; Aielli, G; Akatsuka, S; Akesson, TPA; Akilli, E; Akimov, AV; Al Khoury, K; Alberghi, GL; Albert, J; Alconada Verzini, MJ; Alderweireldt, S; Aleksa, M; Aleksandrov, IN; Alexa, C; Alexandre, D; Alexopoulos, T; Alfonsi, A; Alhroob, M; Ali, B; Alimonti, G; Alison, J; Alkire, SP; Allaire, C; Allbrooke, BMM; Allen, BW; Allport, PP; Aloisio, A; Alonso, A; Alonso, F; Alpigiani, C; Alshehri, AA; Alvarez Estevez, M; Alvarez Piqueras, D; Alviggi, MG; Amaral Coutinho, Y; Ambler, A; Ambroz, L; Amelung, C; Amidei, D; Amor Dos Santos, SP; Amoroso, S; Amrouche, CS; An, F; Anastopoulos, C; Andari, N; Andeen, T; Anders, CF; Anders, JK; Andreazza, A; Andrei, V; Anelli, CR | Abstract: © 2020, The Author(s). A mistake was identified for the paper [1] in the treatment of the radion [2] cross-sections, which resulted in multiple changes.
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TL;DR: A misinterpretation in the comparison between the reported new ATLAS measurement of the process pp → Xp and previously published CMS data resulted in the measurement corresponding to cases where either proton dissociates.
Abstract: Figure 5b of the paper [1] contained a misinterpretation in the comparison between the reported new ATLAS measurement of the process pp -> Xp and previously published CMS data [2]. The ATLAS mea ...
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TL;DR: The continuing work to optimise both local and remote data access by testing different caching methods at the RAL Tier-1 sites is described.
Abstract: The XRootD software framework is essential for data access at WLCG sites. The WLCG community is exploring and expanding XRootD functionality. This presents a particular challenge at the RAL Tier-1 as the Echo storage service is a Ceph based Erasure Coded object store. External access to Echo uses gateway machines which run GridFTP and caching servers. Local jobs access Echo via caches on every worker node, but it is clear there are inefficiencies in the system. Remote jobs also access data via XRootD on Echo. For CMS jobs this is via the AAA service. ATLAS, who are consolidating their storage at fewer sites, are increasingly accessing job input data remotely. This paper describes the continuing work to optimise both local and remote data access by testing different caching methods.