Estimation of backgrounds from jets misidentified as τ-leptons using the Universal Fake Factor method with the ATLAS detector G. Aad, E. Aakvaag, B. Abbott, S. Abdelhameed, K. Abeling, et al. European Physical Journal C, 2025 Processes with $$\\tau $$ τ -leptons in the final state are important for Standard Model measurements and searches for physics beyond the Standard Model. The ATLAS experiment at the Large Hadron Collider observes $$\\tau $$ τ -leptons produced in proton–proton collisions only through their decay products. Data analyses involving hadronically decaying $$\\tau $$ τ -leptons face challenges due to backgrounds from jets misidentified as $$\\tau $$ τ -leptons that are not modelled reliably by Monte Carlo simulations. Data-driven methods such as the fake-factor method allow such misidentified backgrounds to be predicted by measuring transfer factors, known as fake factors, in data from dedicated regions. This paper describes a refined technique for determining the fake factors, the Universal Fake Factor method. It evaluates the fake factors for a signal region by using fake factors from samples enriched in different sources of jets misidentified as $$\\tau $$ τ -leptons (light-quark, gluon, b -quark, and pile-up jets). Each fake factor is calculated as a linear combination of fake factors measured in these different enriched samples. For the full Run 2 data set, the systematic uncertainty of the calculated fake factors, evaluated using $$W(\\mu \\nu )$$ W ( μ ν ) enriched event sample, ranges from 15 to 35% depending on the $$\\tau $$ τ -lepton’s transverse momentum and charged-particle decay multiplicity.
Total Cost of Ownership and Evaluation of Google Cloud Resources for the ATLAS Experiment at the LHC G. Aad, E. Aakvaag, B. Abbott, S. Abdelhameed, K. Abeling, et al. Computing and Software for Big Science, 2025 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 events with one displaced vertex from long-lived neutral particles decaying into hadronic jets in the ATLAS muon spectrometer in pp collisions at (Formula presented) = 13 TeV G. Aad, E. Aakvaag, B. Abbott, S. Abdelhameed, K. Abeling, et al. Physical Review D, 2025 A search for events with one displaced vertex from long-lived particles using data collected by the ATLAS detector at the Large Hadron Collider is presented, using 140 fb − 1 of proton-proton collision data at s = 13 TeV recorded in 2015–2018. The search employs techniques for reconstructing vertices of long-lived particles decaying into hadronic jets in the muon spectrometer displaced between 3 m and 14 m from the primary interaction vertex. The observed number of events is consistent with the expected background and limits for several benchmark signals are determined. A scalar-portal model and a Higgs-boson-portal baryogenesis model are considered. A dedicated analysis channel is employed to target Z-boson associated long-lived particle production, including an axionlike particle and a dark photon model. For the Higgs boson model, branching fractions above 1% are excluded at 95% confidence level for long-lived particle proper decay lengths ranging from 5 cm to 40 m. For the photophobic axionlike particle model considered, this search produces the strongest limits to date for proper decay lengths greater than O ( 10 ) cm .
Measurement of the ttproduction cross-section using eμ events with b-tagged jets in ppcollisions at √s=13 TeV with the ATLAS detector Physics Letters Section B Nuclear Elementary Particle and High Energy Physics, 2016
