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UC Santa Cruz

Open Access Policy Deposits

This series is automatically populated with publications deposited by UC Santa Cruz Department of Physics researchers in accordance with the University of California’s open access policies. For more information see Open Access Policy Deposits and the UC Publication Management System.

Total Cost of Ownership and Evaluation of Google Cloud Resources for the ATLAS Experiment at the LHC

(2025)

Abstract: The ATLAS Google Project was established as part of an ongoing evaluation of the use of commercial clouds by the ATLAS Collaboration, in anticipation of the potential future adoption of such resources by WLCG grid sites to fulfil or complement their computing pledges. Seamless integration of Google cloud resources into the worldwide ATLAS distributed computing infrastructure was achieved at large scale and for an extended period of time, and hence cloud resources are shown to be an effective mechanism to provide additional, flexible computing capacity to ATLAS. For the first time a total cost of ownership analysis has been performed, to identify the dominant cost drivers and explore effective mechanisms for cost control. Network usage significantly impacts the costs of certain ATLAS workflows, underscoring the importance of implementing such mechanisms. Resource bursting has been successfully demonstrated, whilst exposing the true cost of this type of activity. A follow-up to the project is underway to investigate methods for improving the integration of cloud resources in data-intensive distributed computing environments and reducing costs related to network connectivity, which represents the primary expense when extensively utilising cloud resources.

Search for a light charged Higgs boson in t→H±b decays, with H±→cs, in pp collisions at s=13TeV with the ATLAS detector

(2025)

Abstract: A search for a light charged Higgs boson produced in decays of the top quark, $$t \rightarrow H^{\pm } b$$ t → H ± b with $$H^{\pm } \rightarrow cs$$ H ± → c s , is presented. This search targets the production of top-quark pairs $$t\bar{t} \rightarrow Wb H^{\pm } b$$ t t ¯ → W b H ± b , with $$W \rightarrow \ell u $$ W → ℓ ν ( $$\ell = e, \mu $$ ℓ = e , μ ), resulting in a lepton-plus-jets final state characterised by an isolated electron or muon and at least four jets. The search exploits b-quark and c-quark identification techniques as well as multivariate methods to suppress the dominant $$t\bar{t}$$ t t ¯ background. The data analysed correspond to $$140\hbox { fb}^{-1}$$ 140 fb - 1 of $$pp$$ pp collisions at $$\sqrt{s} = 13\hbox { TeV}$$ s = 13 TeV recorded with the ATLAS detector at the LHC between 2015 and 2018. Observed (expected) 95% confidence-level upper limits on the branching fraction $$\mathscr {B}(t\rightarrow H^{\pm } b)$$ B ( t → H ± b ) , assuming $$\mathscr {B}(t\rightarrow Wb) + \mathscr {B}(t \rightarrow H^{\pm } (\rightarrow cs)b)=1.0$$ B ( t → W b ) + B ( t → H ± ( → c s ) b ) = 1.0 , are set between 0.066% (0.077%) and 3.6% (2.3%) for a charged Higgs boson with a mass between 60 and 168 GeV.

Design and performance of the balloon-borne magnetic spectrometer AESOP-Lite

(2025)
Cover page of Constraint on the total width of the Higgs boson from Higgs boson and four-top-quark measurements in pp collisions at s = 13 TeV with the ATLAS detector

Constraint on the total width of the Higgs boson from Higgs boson and four-top-quark measurements in pp collisions at s = 13 TeV with the ATLAS detector

(2025)

This Letter presents a constraint on the total width of the Higgs boson (ΓH) using a combined measurement of on-shell Higgs boson production and the production of four top quarks, which involves contributions from off-shell Higgs boson-mediated processes. This method relies on the assumption that the tree-level Higgs-top Yukawa coupling strength is the same for on-shell and off-shell Higgs boson production processes, thereby avoiding any assumptions about the relationship between on-shell and off-shell gluon fusion Higgs production rates, which were central to previous measurements. The result is based on up to 140 fb−1 of proton–proton collisions at a centre-of-mass energy of s = 13 TeV collected with the ATLAS detector at the Large Hadron Collider. The observed (expected) 95% confidence level upper limit on ΓH is 450 MeV (75 MeV). Additionally, considering the constraint on the Higgs-top Yukawa coupling from loop-induced Higgs boson production and decay processes further yields an observed (expected) upper limit of 160 MeV (55 MeV).

Cover page of Measurement of tt¯ production in association with additional b-jets in the eμ final state in proton–proton collisions at s = 13 TeV with the ATLAS detector

Measurement of tt¯ production in association with additional b-jets in the eμ final state in proton–proton collisions at s = 13 TeV with the ATLAS detector

(2025)

Abstract : This paper presents measurements of top-antitop quark pair ( $$ t\overline{t} $$ t t ¯ ) production in association with additional b-jets. The analysis utilises 140 fb −1 of proton–proton collision data collected with the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy of 13 TeV. Fiducial cross-sections are extracted in a final state featuring one electron and one muon, with at least three or four b-jets. Results are presented at the particle level for both integrated cross-sections and normalised differential cross-sections, as functions of global event properties, jet kinematics, and b-jet pair properties. Observable quantities characterising b-jets originating from the top quark decay and additional b-jets are also measured at the particle level, after correcting for detector effects. The measured integrated fiducial cross-sections are consistent with $$ t\overline{t}b\overline{b} $$ t t ¯ b b ¯ predictions from various next-to-leading-order matrix element calculations matched to a parton shower within the uncertainties of the predictions. State-of-the-art theoretical predictions are compared with the differential measurements; none of them simultaneously describes all observables. Differences between any two predictions are smaller than the measurement uncertainties for most observables.

Cover page of Search for diphoton resonances in the 66 to 110 GeV mass range using pp collisions at s = 13 TeV with the ATLAS detector

Search for diphoton resonances in the 66 to 110 GeV mass range using pp collisions at s = 13 TeV with the ATLAS detector

(2025)

Abstract : A search is performed for light, spin-0 bosons decaying into two photons in the 66 to 110 GeV mass range, using 140 fb −1 of proton-proton collisions at $$ \sqrt{s} $$ s = 13 TeV produced by the Large Hadron Collider and collected by the ATLAS detector. Multivariate analysis techniques are used to define event categories that improve the sensitivity to new resonances beyond the Standard Model. A model-independent search for a generic spin-0 particle and a model-dependent search for an additional low-mass Higgs boson are performed in the diphoton invariant mass spectrum. No significant excess is observed in either search. Mass-dependent upper limits at the 95% confidence level are set in the model-independent scenario on the fiducial cross-section times branching ratio into two photons in the range of 8 fb to 53 fb. Similarly, in the model-dependent scenario upper limits are set on the total cross-section times branching ratio into two photons as a function of the Higgs boson mass in the range of 19 fb to 102 fb.

Cover page of Combination of searches for singly and doubly charged Higgs bosons produced via vector-boson fusion in proton–proton collisions at s = 13 TeV with the ATLAS detector

Combination of searches for singly and doubly charged Higgs bosons produced via vector-boson fusion in proton–proton collisions at s = 13 TeV with the ATLAS detector

(2025)

A combination of searches for singly and doubly charged Higgs bosons, H± and H±±, produced via vector-boson fusion is performed using 140 fb−1 of proton–proton collisions at a centre-of-mass energy of 13 TeV, collected with the ATLAS detector during Run 2 of the Large Hadron Collider. Searches targeting decays to massive vector bosons in leptonic final states (electrons or muons) are considered. New constraints are reported on the production cross-section times branching fraction for charged Higgs boson masses between 200 GeV and 3000 GeV. The results are interpreted in the context of the Georgi-Machacek model for which the most stringent constraints to date are set for the masses considered in the combination.

Cover page of Measurement of top-quark pair production in association with charm quarks in proton–proton collisions at s = 13 TeV with the ATLAS detector

Measurement of top-quark pair production in association with charm quarks in proton–proton collisions at s = 13 TeV with the ATLAS detector

(2025)

Inclusive cross-sections for top-quark pair production in association with charm quarks are measured with proton–proton collision data at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 140 fb−1, collected with the ATLAS experiment at the LHC between 2015 and 2018. The measurements are performed by requiring one or two charged leptons (electrons and muons), two b-tagged jets, and at least one additional jet in the final state. A custom flavor-tagging algorithm is employed for the simultaneous identification of b-jets and c-jets. In a fiducial phase space that replicates the acceptance of the ATLAS detector, the cross-sections for tt¯+≥2c and tt¯+1c production are measured to be 1.28−0.24+0.27pb and 6.4−0.9+1.0pb, respectively. The measurements are primarily limited by uncertainties in the modeling of inclusive tt¯ and tt¯+bb¯ production, in the calibration of the flavor-tagging algorithm, and by data statistics. Cross-section predictions from various tt¯ simulations are largely consistent with the measured cross-section values, though all underpredict the observed values by 0.5 to 2.0 standard deviations. In a phase-space volume without requirements on the tt¯ decay products and the jet multiplicity, the cross-section ratios of tt¯+≥2c and tt¯+1c to total tt¯+jets production are determined to be (1.23±0.25)% and (8.8±1.3)%.

Combination of searches for singly produced vectorlike top quarks in pp collisions at s=13 TeV with the ATLAS detector

(2025)

A combination of searches for the single production of vectorlike top quarks (T) is presented. These analyses are based on proton-proton collisions at s=13  TeV recorded in 2015–2018 with the ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of 139  fb−1. The T decay modes considered in this combination are into a top quark and either a Standard Model Higgs boson or a Z boson (T→Ht and T→Zt). The individual searches used in the combination are differentiated by the number of leptons (e, μ) in the final state. The observed data are found to be in good agreement with the Standard Model background prediction. Interpretations are provided for a range of masses and couplings of the vectorlike top quark for benchmark models and generalized representations in terms of 95% confidence level limits. For a benchmark signal prediction of a vectorlike top quark SU(2) singlet with electroweak coupling, κ, of 0.5, masses below 2.1 TeV are excluded, resulting in the most restrictive limits to date. © 2025 CERN, for the ATLAS Collaboration 2025 CERN

Cover page of Simultaneous Unbinned Differential Cross-Section Measurement of Twenty-Four Z+jets Kinematic Observables with the ATLAS Detector

Simultaneous Unbinned Differential Cross-Section Measurement of Twenty-Four Z+jets Kinematic Observables with the ATLAS Detector

(2024)

Z boson events at the Large Hadron Collider can be selected with high purity and are sensitive to a diverse range of QCD phenomena. As a result, these events are often used to probe the nature of the strong force, improve Monte Carlo event generators, and search for deviations from standard model predictions. All previous measurements of Z boson production characterize the event properties using a small number of observables and present the results as differential cross sections in predetermined bins. In this analysis, a machine learning method called omnifold is used to produce a simultaneous measurement of twenty-four Z+jets observables using 139  fb^{-1} of proton-proton collisions at sqrt[s]=13  TeV collected with the ATLAS detector. Unlike any previous fiducial differential cross-section measurement, this result is presented unbinned as a dataset of particle-level events, allowing for flexible reuse in a variety of contexts and for new observables to be constructed from the twenty-four measured observables.

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