517 research outputs found

    Firmware implementation of a recurrent neural network for the computation of the energy deposited in the liquid argon calorimeter of the ATLAS experiment

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    International audienceThe ATLAS experiment measures the properties of particles that are products of proton-proton collisions at the LHC. The ATLAS detector will undergo a major upgrade before the high luminosity phase of the LHC. The ATLAS liquid argon calorimeter measures the energy of particles interacting electromagnetically in the detector. The readout electronics of this calorimeter will be replaced during the aforementioned ATLAS upgrade. The new electronic boards will be based on state-of-the-art field-programmable gate arrays (FPGA) from Intel allowing the implementation of neural networks embedded in firmware. Neural networks have been shown to outperform the current optimal filtering algorithms used to compute the energy deposited in the calorimeter. This article presents the implementation of a recurrent neural network (RNN) allowing the reconstruction of the energy deposited in the calorimeter on Stratix 10 FPGAs. The implementation in high level synthesis (HLS) language allowed fast prototyping but fell short of meeting the stringent requirements in terms of resource usage and latency. Further optimisations in Very High-Speed Integrated Circuit Hardware Description Language (VHDL) allowed fulfilment of the requirements of processing 384 channels per FPGA with a latency smaller than 125 ns

    Measurements of the suppression and correlations of dijets in Xe+Xe collisions at Formula Presented TeV

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    Measurements of the suppression and correlations of dijets is performed using 3 μ b − 1 of Xe+Xe data at s N N = 5.44 TeV collected with the ATLAS detector at the CERN Large Hadron Collider. Dijets with jets reconstructed using the R = 0.4 anti- k t algorithm are measured differentially in jet p T over the range of 32 to 398 GeV and the centrality of the collisions. Significant dijet momentum imbalance is found in the most central Xe+Xe collisions, which decreases in more peripheral collisions. Results from the measurement of per-pair normalized and absolutely normalized dijet p T balance are compared with previous Pb + Pb measurements at s N N = 5.02 TeV. The differences between the dijet suppression in Xe+Xe and Pb + Pb are further quantified by the ratio of pair nuclear-modification factors. The results are found to be consistent with those measured in Pb + Pb data when compared in classes of the same event activity and when taking into account the difference between the center-of-mass energies of the initial parton scattering process in Xe+Xe and Pb + Pb collisions. These results should provide input for a better understanding of the role of energy density, system size, path length, and fluctuations in the parton energy loss

    Underlying-event studies with strange hadrons in pp collisions at s=13 TeV with the ATLAS detector

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    Properties of the underlying-event in pp interactions are investigated primarily via the strange hadrons KS0, Λ and Λ¯, as reconstructed using the ATLAS detector at the LHC in minimum-bias pp collision data at s=13 TeV. The hadrons are reconstructed via the identification of the displaced two-particle vertices corresponding to the decay modes, Λ→π-p and Λ¯→π+p¯. These are used in the construction of underlying-event observables in azimuthal regions computed relative to the leading charged-particle jet in the event. None of the hadronisation and underlying-event physics models considered can describe the data over the full kinematic range considered. Events with a leading charged-particle jet in the range of 10<pT≤40 GeV are studied using the number of prompt charged particles in the transverse region. The ratio N(Λ+Λ¯)/N(KS0) as a function of the number of such charged particles varies only slightly over this range. This disagrees with the expectations of some of the considered Monte Carlo models

    Search for heavy Majorana neutrinos in e±e±e^{\pm} e^{\pm} and e±μ±e^{\pm} \mu^{\pm} final states via WW scattering in pppp collisions at s=13\sqrt{s}=13 TeV with the ATLAS detector

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    International audienceA search for heavy Majorana neutrinos in scattering of same-sign WW boson pairs in proton-proton collisions at s=13\sqrt{s}= 13 TeV at the LHC is reported. The dataset used corresponds to an integrated luminosity of 140 fb1^{-1}, collected with the ATLAS detector during 2015-2018. The search is performed in final states including a same-sign eeee or eμe\mu pair and at least two jets with large invariant mass and a large rapidity difference. No significant excess of events with respect to the Standard Model background predictions is observed. The results are interpreted in a benchmark scenario of the Phenomenological Type-I Seesaw model. New constraints are set on the values of the VeN2\vert V_{e N} \vert^{2} and VeNVμN\vert V_{e N} V^{*}_{\mu N} \vert parameters for heavy Majorana neutrino masses between 50 GeV and 20 TeV, where VNV_{\ell N} is the matrix element describing the mixing of the heavy Majorana neutrino mass eigenstate with the Standard Model neutrino of flavour =e,μ\ell = e, \mu. The sensitivity to the Weinberg operator is investigated and constraints on the effective eeee and eμe\mu Majorana neutrino masses are reported. The statistical combination of the eeee and eμe\mu channels with the previously published μμ\mu\mu channel is performed

    Measurements of longitudinal flow decorrelations in pppp and Xe+Xe collisions with the ATLAS detector

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    Measurements of longitudinal flow decorrelations in 13 TeV pppp and 5.44 TeV Xe+Xe collisions with the ATLAS detector are presented. The measurements are performed using the two-particle correlation method, combining charged-particle tracks within |\eta| < 2.5 with either calorimeter energy clusters or towers within 4.0<|\eta|<4.9. A template-based subtraction procedure is used to remove non-flow effects in both the pppp and the Xe+Xe analyses. The dependence of the longitudinal flow decorrelations on the pseudorapidity separation between the particles is characterized via the slope parameter FnF_n for the elliptic (n=2n=2) and triangular (n=3n=3) harmonic moments. The results are reported as a function of charged-particle multiplicity for the pppp and Xe+Xe collision systems. Comparing the data to a color string-based model of the initial geometry indicates that in pppp and peripheral Xe+Xe collisions, sub-nucleonic structure and fluctuations in longitudinal energy deposition are needed to describe the data

    Measurements of longitudinal flow decorrelations in pppp and Xe+Xe collisions with the ATLAS detector

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    International audienceMeasurements of longitudinal flow decorrelations in 13 TeV pppp and 5.44 TeV Xe+Xe collisions with the ATLAS detector are presented. The measurements are performed using the two-particle correlation method, combining charged-particle tracks within η<2.5|\eta| < 2.5 with either calorimeter energy clusters or towers within 4.0<η<4.94.0<|\eta|<4.9. A template-based subtraction procedure is used to remove non-flow effects in both the pppp and the Xe+Xe analyses. The dependence of the longitudinal flow decorrelations on the pseudorapidity separation between the particles is characterized via the slope parameter FnF_n for the elliptic (n=2n=2) and triangular (n=3n=3) harmonic moments. The results are reported as a function of charged-particle multiplicity for the pppp and Xe+Xe collision systems. Comparing the data to a color string-based model of the initial geometry indicates that in pppp and peripheral Xe+Xe collisions, sub-nucleonic structure and fluctuations in longitudinal energy deposition are needed to describe the data

    Test of CP invariance in Higgs boson vector-boson-fusion production using the H → γγ channel with the ATLAS detector

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    A test of C P invariance in Higgs boson production via vector-boson fusion has been performed in the H → γ γ channel using 139     fb − 1 of proton-proton collision data at √ s = 13     TeV collected by the ATLAS detector at the LHC. The optimal observable method is used to probe the C P structure of interactions between the Higgs boson and electroweak gauge bosons, as described by an effective field theory. No sign of C P violation is observed in the data. Constraints are set on the parameters describing the strength of the C P -odd component in the coupling between the Higgs boson and the electroweak gauge bosons in two effective field theory bases: ˜ d in the HISZ basis and c H ˜ W in the Warsaw basis. The results presented are the most stringent constraints on C P violation in the coupling between Higgs and weak bosons. The 95% C.L. constraint on ˜ d is derived for the first time and the 95% C.L. constraint on c H ˜ W has been improved by a factor of 5 compared to the previous measurement

    Search for a resonance decaying into a scalar particle and a Higgs boson in final states with leptons and two photons in proton-proton collisions at s = 13 TeV with the ATLAS detector

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    A search for a hypothetical heavy scalar particle, X, decaying into a singlet scalar particle, S, and a Standard Model Higgs boson, H, using 140 fb−1 of proton-proton collision data at the centre-of-mass energy of 13 TeV recorded with the ATLAS detector at the LHC is presented. The explored mass range is 300 ≤ mX ≤ 1000 GeV and 170 ≤ mS ≤ 500 GeV. The signature of this search is one or two leptons (e or μ) from the decay of vector bosons originating from the S particle, S → W±W∓/ZZ, and two photons from the Higgs boson decay, H → γγ. No significant excess is observed above the expected Standard Model background. The observed (expected) upper limits at the 95% confidence level on the cross- section for gg → X → SH, assuming the same S → WW/ZZ branching ratios as for a SM-like heavy Higgs boson, are between 530 (800) fb and 120 (170) fb

    Measurement of vector boson production cross sections and their ratios using pp collisions at √s=13.6 TeV with the ATLAS detector

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    Fiducial and total W± and Z boson cross sections, their ratios and the ratio of top-antitop-quark pair and W-boson fiducial cross sections are measured in proton–proton collisions at a centre-of-mass energy of s=13.6 TeV, corresponding to an integrated luminosity of 29 fb−1 of data collected in 2022 by the ATLAS experiment at the Large Hadron Collider. The measured fiducial cross-section values for W+→l+ν, W−→l−ν ̄, and Z→l+l− (l=e or μ) boson productions are 4250±150 pb, 3310±120 pb, and 744±20 pb, respectively, where the uncertainty is the total uncertainty, including that arising from the luminosity of about 2.2%. The measurements are in agreement with Standard-Model predictions calculated at next-to-next-to-leading-order in αs, next-to-next-to-leading logarithmic accuracy and next-to-leading-order electroweak accuracy

    Search for boosted low-mass resonances decaying into hadrons produced in association with a photon in pp collisions at s = 13 TeV with the ATLAS detector

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    Many extensions of the Standard Model, including those with dark matter particles, propose new mediator particles that decay into hadrons. This paper presents a search for such low mass narrow resonances decaying into hadrons using 140 fb−1 of proton-proton collision data recorded with the ATLAS detector at a centre-of-mass energy of 13 TeV. The resonances are searched for in the invariant mass spectrum of large-radius jets with two-pronged substructure that are recoiling against an energetic photon from initial state radiation, which is used as a trigger to circumvent limitations on the maximum data recording rate. This technique enables the search for boosted hadronically decaying resonances in the mass range 20–100 GeV hitherto unprobed by the ATLAS Collaboration. The observed data are found to agree with Standard Model predictions and 95% confidence level upper limits are set on the coupling of a hypothetical new spin-1 Z′ resonance with Standard Model quarks as a function of the assumed Z′-boson mass in the range between 20 and 200 GeV
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