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Öğe Calibration of a soft secondary vertex tagger using proton-proton collisions at Formula Presented with the ATLAS detector(American physical society, 2024) Aad, G.; Aakvaag, E.; Abbott, B.; Beddall, Andrew John; Çetin, Serkant Ali; Öztürk, Sertaç; Şimşek, Sinem; Uysal, Zekeriya; Çelebi, EmreSeveral processes studied by the ATLAS experiment at the Large Hadron Collider produce low-momentum Formula Presented-flavored hadrons in the final state. This paper describes the calibration of a dedicated tagging algorithm that identifies Formula Presented-flavored hadrons outside of hadronic jets by reconstructing the soft secondary vertices originating from their decays. The calibration is based on a proton-proton collision dataset at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of Formula Presented. Scale factors used to correct the algorithm’s performance in simulated events are extracted for the Formula Presented-tagging efficiency and the mistag rate of the algorithm using a data sample enriched in Formula Presented events. Several orthogonal measurement regions are defined, binned as a function of the multiplicities of soft secondary vertices and jets containing a Formula Presented-flavored hadron in the event. The mistag rate scale factors are estimated separately for events with low and high average numbers of interactions per bunch crossing. The results, which are derived from events with low missing transverse momentum, are successfully validated in a phase space characterized by high missing transverse momentum and therefore are applicable to new physics searches carried out in either phase space regime.Öğe Constraint on the total width of the Higgs boson from Higgs boson and four-top-quark measurements in pp collisions at = 13 TeV with the ATLAS detector(Elsevier B.V., 2025) Aad, G.; Aakvaag, E.; Abbott, B.; Beddall, Andrew John; Çelebi,; Öztürk, Sertaç; Şahinsoy, Merve; Şimşek, Sinem; Uysal, ZekeriyaThis 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). © 2025 CERN for the benefit of the ATLAS CollaborationÖğe Differential cross-sections for events with missing transverse momentum and jets measured with the ATLAS detector in 13 TeV proton-proton collisions(Springer Science and Business Media Deutschland GmbH, 2024) Aad, G.; Aakvaag, E.; Abbott, B.; Uysal, Zekariya; Beddall, Andrew John; Çetin, Serkant Ali; Öztürk, Sertaç; Şimşek, SinemMeasurements of inclusive, differential cross-sections for the production of events with missing transverse momentum in association with jets in proton-proton collisions at s = 13 TeV are presented. The measurements are made with the ATLAS detector using an integrated luminosity of 140 fb−1 and include measurements of dijet distributions in a region in which vector-boson fusion processes are enhanced. They are unfolded to correct for detector resolution and efficiency within the fiducial acceptance, and are designed to allow robust comparisons with a wide range of theoretical predictions. A measurement of differential cross sections for the Z → νν process is made. The measurements are generally well-described by Standard Model predictions except for the dijet invariant mass distribution. Auxiliary measurements of the hadronic system recoiling against isolated leptons, and photons, are also made in the same phase space. Ratios between the measured distributions are then derived, to take advantage of cancellations in modelling effects and some of the major systematic uncertainties. These measurements are sensitive to new phenomena, and provide a mechanism to easily set constraints on phenomenological models. To illustrate the robustness of the approach, these ratios are compared with two common Dark Matter models, where the constraints derived from the measurement are comparable to those set by dedicated detector-level searches. © The Author(s) 2024.Öğe Measurement of the VH,H → ττ process with the ATLAS detector at 13 TeV(Elsevier B.V., 2024) Aad, G.; Aakvaag, E.; Abbott, B.; Beddall, Andrew John; Çetin, Serkant Ali; Öztürk, Sertaç; Şimşek, Sinem; Uysal, ZekeriyaA measurement of the Standard Model Higgs boson produced in association with a W or Z boson and decaying into a pair of τ-leptons is presented. This search is based on proton-proton collision data collected at s=13 TeV by the ATLAS experiment at the LHC corresponding to an integrated luminosity of 140 fb−1. For the Higgs boson candidate, only final states with at least one τ-lepton decaying hadronically (τ→hadrons+ντ) are considered. For the vector bosons, only leptonic decay channels are considered: Z→ℓℓ and W→ℓνℓ, with ℓ=e,μ. An excess of events over the expected background is found with an observed (expected) significance of 4.2 (3.6) standard deviations, providing evidence of the Higgs boson produced in association with a vector boson and decaying into a pair of τ-leptons. The ratio of the measured cross-section to the Standard Model prediction is μVHττ=1.28−0.29+0.30(stat.)−0.21+0.25(syst.). This result represents the most accurate measurement of the VH(ττ) process achieved to date. © 2024 The Author(s)Öğe Measurement of vector boson production cross sections and their ratios using pp collisions at √s=13.6 TeV with the ATLAS detector(Elsevier, 2024) Aad, G.; Aakvaag, E.; Abbott, B.; Beddall, Andrew John; Çetin, Serkant Ali; Öztürk, Sertaç; Şimşek, Sinem; Uysal, ZekeriyaFiducial and total W+ and Z boson cross sections, their ratios and the ratio of top-antitop-quark pair and.. -boson fiducial cross sections are measured in proton-proton collisions at a centre-of-mass energy of root 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(+) v, W- -> l(-) v- , and Z -> l(+)l(-) (l =e or mu) 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 alpha(s) ,next-to-nextto-leading logarithmic accuracy and next-to-leading-order electroweak accuracy.Öğe Search for dark matter produced in association with a Higgs boson decaying to tau leptons at ?s=13 TeV with the ATLAS detector(Springer, 2023) Aad, G.; Aakvaag, E.; Abbott, B.; Abeling, K.; Abidi, S. H.; Aboulhorma, A.; Çetin, Serkant AliA search for dark matter produced in association with a Higgs boson in final states with two hadronically decaying tau-leptons and missing transverse momentum is presented. The analysis uses 139 fb(-1) of proton-proton collision data at root s = 13 TeV collected by the ATLAS experiment at the Large Hadron Collider between 2015 and 2018. No evidence of physics beyond the Standard Model is found. The results are interpreted in terms of a 2HDM+a model featuring two scalar Higgs doublets and a pseudoscalar singlet field. Exclusion limits on the parameters of the model in selected benchmark scenarios are derived at 95% confidence level. Model-independent limits are also set on the visible cross-section for processes beyond the Standard Model producing missing transverse momentum in association with a Higgs boson decaying into tau-leptons.Öğe Searches for exclusive Higgs boson decays into D⁎γ and Z boson decays into D0γ and Ks 0γ in pp collisions at s=13TeV with the ATLAS detector(Elsevier, 2024) Aad, G.; Aakvaag, E.; Abbott, B.; Beddall, Andrew John; Çetin, Serkant Ali; Öztürk, Sertaç; Şimşek, Sinem; Uysal, ZekeriyaSearches for exclusive decays of the Higgs boson into D⁎γ and of the Z boson into D0γ and Ks 0γ can probe flavour-violating Higgs boson and Z boson couplings to light quarks. Searches for these decays are performed with a pp collision data sample corresponding to an integrated luminosity of 136.3 fb−1 collected at s=13TeV between 2016–2018 with the ATLAS detector at the CERN Large Hadron Collider. In the D⁎γ and D0γ channels, the observed (expected) 95% confidence-level upper limits on the respective branching fractions are B(H→D⁎γ)<1.0(1.2)×10−3, B(Z→D0γ)<4.0(3.4)×10−6, while the corresponding results in the Ks 0γ channel are B(Z→Ks 0γ)<3.1(3.0)×10−6.
