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The Worldwide LHC Computing Grid (WLCG) is today comprised of a range of different types of resources such as cloud centers, large and small HPC centers, volunteer computing as well as the traditional grid resources. The Nordic Tier 1 (NT1) is a WLCG computing infrastructure distributed over the Nordic countries. The NT1 deploys the Nordugrid ARC-CE, which is non-intrusive and lightweight, originally developed to cater for HPC centers where no middleware could be installed on the worker nodes. The NT1 runs ARC in the native Nordugrid mode which contrary to the Pilot mode leaves jobs data transfers up to ARC. ARCs data transfer capabilities together with the ARC Cache are the most important features of ARC. In this article we will describe the datastaging and cache functionality of the ARC-CE set up as an edge service to an HPC or cloud resource, and show the gain in efficiency this model provides compared to a traditional pilot model, especially for sites with remote storage.

A search for the supersymmetric partners of quarks and gluons (squarks and gluinos) in final states containing jets and missing transverse momentum, but no electrons or muons, is presented. The data used in this search were recorded by the ATLAS experiment in proton-proton collisions at a centre-of-mass energy of root s = 13 TeV during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb(-1). The results are interpreted in the context of various R-parity-conserving models where squarks and gluinos are produced in pairs or in association and a neutralino is the lightest supersymmetric particle. An exclusion limit at the 95% confidence level on the mass of the gluino is set at 2.30 TeV for a simplified model containing only a gluino and the lightest neutralino, assuming the latter is massless. For a simplified model involving the strong production of mass-degenerate first- and second-generation squarks, squark masses below 1.85 TeV are excluded if the lightest neutralino is massless. These limits extend substantially beyond the region of supersymmetric parameter space excluded previously by similar searches with the ATLAS detector.

This paper describes a measurement of light-by-light scattering based on Pb+Pb collision data recorded by the ATLAS experiment during Run 2 of the LHC. The study uses 2.2 nb(-1) of integrated luminosity collected in 2015 and 2018 at root sNN = 5.02TeV. Light-by-light scattering candidates are selected in events with two photons produced exclusively, each with transverse energy E-T(gamma) > 2.5 GeV, pseudorapidity vertical bar eta(gamma)vertical bar < 2.37, diphoton invariant mass m(gamma gamma) > 5 GeV, and with small diphoton transverse momentum and diphoton acoplanarity. The integrated and differential fiducial cross sections are measured and compared with theoretical predictions. The diphoton invariant mass distribution is used to set limits on the production of axion-like particles. This result provides the most stringent limits to date on axion-like particle production for masses in the range 6-100 GeV. Cross sections above 2 to 70 nb are excluded at the 95% CL in that mass interval.

Cross-sections for the production of a Z boson in association with two photons are measured in proton-proton collisions at a centre-of-mass energy of 13 TeV. The data used correspond to an integrated luminosity of 139 fb(-1) recorded by the ATLAS experiment during Run 2 of the LHC. The measurements use the electron and muon decay channels of the Z boson, and a fiducial phase-space region where the photons are not radiated from the leptons. The integrated Z(-> ll)gamma gamma cross-section is measured with a precision of 12% and differential cross-sections are measured as a function of six kinematic variables of the Z gamma gamma system. The data are compared with predictions from MC event generators which are accurate to up to next-to-leading order in QCD. The cross-section measurements are used to set limits on the coupling strengths of dimension-8 operators in the framework of an effective field theory.

This paper presents measurements of top-antitop quark pair (t¯t) production inassociation with additional b-jets. The analysis utilises 140 fb −1 of proton–proton collisiondata collected with the ATLAS detector at the Large Hadron Collider at a centre-of-massenergy of 13 TeV. Fiducial cross-sections are extracted in a final state featuring one electronand one muon, with at least three or four b-jets . Results are presented at the particle level forboth integrated cross-sections and normalised differential cross-sections, as functions of globalevent properties, jet kinematics, and b-jet pair properties. Observable quantities characterisingb-jets originating from the top quark decay and additional b-jets are also measured at theparticle level, after correcting for detector effects. The measured integrated fiducial cross-sections are consistent with t¯tb¯b predictions from various next-to-leading-order matrix elementcalculations matched to a parton shower within the uncertainties of the predictions. State-of-the-art theoretical predictions are compared with the differential measurements; none ofthem simultaneously describes all observables. Differences between any two predictions aresmaller than the measurement uncertainties for most observables.

A measurement of the top-quark pole mass m t pole is presented in tt <over bar> events with an additional jet, tt <over bar>+ 1-jet, produced in pp collisions at √s = 13TeV. The data sample, recorded with the ATLAS experiment during Run 2 of the LHC, corresponds to an integrated luminosity of 140 fb -1 . Events with one electron and one muon of opposite electric charge in the final state are selected to measure the tt <over bar>+ 1-jet differential cross-section as a function of the inverse of the invariant mass of the tt <over bar> + 1-jet system. Iterative Bayesian Unfolding is used to correct the data to enable comparison with fixed-order calculations at next-to-leading-order accuracy in the strong coupling. The process pp → tt <over bar> j (2 → 3), where top quarks are taken as stable particles, and the process pp → bb <over bar>l + νl - ν<over bar> j (2 → 7), which includes top-quark decays to the dilepton final state and off-shell effects, are considered. The top-quark mass is extracted using χ 2 fit of the unfolded normalized differential cross-section distribution. The results obtained with the 2 → 3 and 2 → 7 calculations are compatible within theoretical uncertainties, providing an important consistency check. The more precise determination is obtained for the 2 → 3 measurement: m t pole = 170.7 ± 0.3 (stat.) ± 1.4 (syst.) ± 0.3 (scale) ±0.2 (PDF ⊕ α S ) GeV, which is in good agreement with other top-quark mass results.

Jets with different radius parameters R are an important tool for probing quantum chromodynamics processes at different angular scales. Jets with small R = 0.2 are instrumental in measurements of the substructure of large-R jets resulting from collimated hadronic decays of energetic W, Z, and Higgs bosons, top quarks, and of potential new resonances. This paper presents measurements of the energy scale, resolution, and associated uncertainties of jets with radius parameters R = 0.2 and 0.6, obtained using the ATLAS detector. The results are based on 37 fb(-1) of proton-proton collision data from the Large Hadron Collider at a centre-of-mass energy of root s = 13 TeV. A new in situ method for measuring jet energy scale differences between data and Monte Carlo simulations is presented. The systematic uncertainties in the jet energy scale for central jets (vertical bar eta vertical bar < 1.2) typically vary from 1% to about 5% as a function of vertical bar eta vertical bar at very low transverse momentum, p(T), of around 20 GeV for both R = 0.2 and 0.6 jets. The relative energy resolution ranges from (35 +/- 6)% at p(T) = 20 GeV to (6 +/- 0.5)% at p(T) = 300 GeV for central R = 0.2 jets, and is found to be slightly worse for R = 0.6 jets. Finally, the effect of close-by hadronic activity on the jet energy scale is investigated and is found to be well modelled by the ATLAS Monte Carlo simulations.

A measurement of the B-0 meson lifetime using B-0 -> J/psi K*(0) decays in data from 13 TeV proton-proton collisions with an integrated luminosity of 140 fb(-1) recorded by the ATLAS detector at the LHC is presented. The measured effective lifetime is tau = 1.5053 +/- 0.0012 (stat.) +/- 0.0035 (syst.) ps. The average decay width extracted from the effective lifetime, using parameters from external sources, is Gamma(d) = 0.6639 +/- 0.0005 (stat.) +/- 0.0016 (syst.) +/- 0.0038 (ext.) ps(-1), where the uncertainties are statistical, systematic and from external sources. The earlier ATLAS measurement of Gamma(s) in the B-s(0) -> J/psi phi decay was used to derive a value for the ratio of the average decay widths Gamma(d) and Gamma(s) for B-0 and B-s(0) mesons respectively, of Gamma(d)/Gamma(s) = 0.9905 +/- 0.0022 (stat.)+/- 0.0036 (syst.)+/- 0.0057 (ext.). Themeasured lifetime, average decay width and decay width ratio are in agreement with theoretical predictions and with measurements by other experiments. This measurement provides the most precise result of the effective lifetime of the B-0 meson to date.

A search is presented for a heavy scalar (H) or pseudo-scalar (A) predicted by the two-Higgs-doublet models, where the H/A is produced in association with a top-quark pair (t t<over bar>H/A), and with the H/A decaying into a tt<over bar> pair. The full LHC Run 2 proton-proton collision data collected by the ATLAS experiment is used, corresponding to an integrated luminosity of 139 fb -1 . Events are selected requiring exactly one or two opposite-charge electrons or muons. Data-driven corrections are applied to improve the modelling of the tt<over bar> +jets background in the regime with high jet and b-jet multiplicities. These include a novel multi-dimensional kinematic reweighting based on a neural network trained using data and simulations. An H/A-mass parameterised graph neural network is trained to optimise the signal-to-background discrimination. In combination with the previous search performed by the ATLAS Collaboration in the multilepton final state, the observed upper limits on the tt<over bar>H/A → tt<over bar>tt<over bar> production cross-section at 95% confidence level range between 14 fb and 5.0 fb for an H/A with mass between 400 GeV and 1000 GeV, respectively. Assuming that both the H and A contribute to the tt<over bar>tt<over bar> cross-section, tan β values below 1.7 or 0.7 are excluded for a mass of 400 GeV or 1000 GeV, respectively. The results are also used to constrain a model predicting the pair production of a colour-octet scalar, with the scalar decaying into a tt<over bar> pair.

Inclusive and differential cross-sections are measured at particle level for the associated production of a top quark pair and a photon (tt<over bar>γ). The analysis is performed using an integrated luminosity of 140 fb -1 of proton-proton collisions at a centre-of-mass energy of 13TeV collected by the ATLAS detector. The measurements are performed in the single-lepton and dilepton top quark pair decay channels focusing on tt<over bar>γ topologies where the photon is radiated from an initial-state parton or one of the top quarks. The absolute and normalised differential cross-sections are measured for several variables characterising the photon, lepton and jet kinematics as well as the angular separation between those objects. The observables are found to be in good agreement with the Monte Carlo predictions. The photon transverse momentum differential distribution is used to set limits on effective field theory parameters related to the electroweak dipole moments of the top quark. The combined limits using the photon and the Z boson transverse momentum measured in tt<over bar> production in associations with a Z boson are also set.