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Öğe Combination of searches for resonant higgs boson pair production using 𝑝𝑝 collisions at √𝑠=13 TeV with the ATLAS detector(American Physical Society, 2024) Filmer, E.K.; Grant, C.M.; Jackson, P; Beddal, Andrew John; Çetin, Serkant Ali; Öztürk, Sertaç; Şimşek, Sinem; Uysal, ZekeriyaA combination of searches for a new resonance decaying into a Higgs boson pair is presented, using up to Formula Presented of Formula Presented collision data at Formula Presented recorded with the ATLAS detector at the LHC. The combination includes searches performed in three decay channels: Formula Presented, Formula Presented, and Formula Presented. No excess above the expected Standard Model background is observed and upper limits are set at the 95% confidence level on the production cross section of Higgs boson pairs originating from the decay of a narrow scalar resonance with mass in the range 251 GeV-5 TeV. The observed (expected) limits are in the range 0.96-600 fb (1.2-390 fb). The limits are interpreted in the type-I two-Higgs-doublet model and the minimal supersymmetric standard model, and constrain parameter space not previously excluded by other searches. © 2024 CERN, for the ATLAS Collaboration.Öğe Observation of an excess of dicharmonium events in the four-muon final state with the ATLAS detector(Amer Physical Soc, 2023) Aad, Georges; Abbott, Braden; Abeling, Kira; Beddall, Andrew John; Çetin, Serkant Ali; Öztürk, Sertaç; Şimşek, SinemA search is made for potential ccc over bar c over bar tetraquarks decaying into a pair of charmonium states in the four ffiffi muon final state using proton-proton collision data at p s = 13 TeV, corresponding to an integrated luminosity of 140 fb-1 recorded by the ATLAS experiment at LHC. Two decay channels, J lig +J lig -4 mu and J lig + ig(2S) -4 mu, are studied. Backgrounds are estimated based on a hybrid approach involving Monte Carlo simulations and data-driven methods. Statistically significant excesses with respect to backgrounds dominated by the single parton scattering are seen in the di-J lig channel consistent with a narrow resonance at 6.9 GeV and a broader structure at lower mass. A statistically significant excess is also seen in the J lig + ig(2S) channel. The fitted masses and decay widths of the structures are reported.Öğe Study of Z ? ll? decays at ?s=8 TeV with the ATLAS detector(Springer, 2024) Aad, G.; Abbott, B.; Abbott, D. C.; Abeling, K.; Abidi, S. H.; Aboulhorma, A.; Çetin, Serkant AliThis paper presents a study of Z -> ll gamma decays with the ATLAS detector at the Large Hadron Collider. The analysis uses a proton-proton data sample corresponding to an integrated luminosity of 20.2 fb(-1) collected at a centre-of-mass energy root s = 8 TeV. Integrated fiducial cross-sections together with normalised differential fiducial cross-sections, sensitive to the kinematics of final-state QED radiation, are obtained. The results are found to be in agreement with state-of-the-art predictions for final-state QED radiation. First measurements of Z -> ll gamma gamma decays are also reported.Öğe Performance of the reconstruction of large impact parameter tracks in the inner detector of ATLAS(Springer, 2023) Aad, G.; Abbott, B.; Abeling, K.; Abicht, N. J.; Abidi, S. H.; Aboulhorma, A.; Çetin, Serkant AliSearches for long-lived particles (LLPs) are among the most promising avenues for discovering physics beyond the Standard Model at the Large Hadron Collider (LHC). However, displaced signatures are notoriously difficult to identify due to their ability to evade standard object reconstruction strategies. In particular, the ATLAS track reconstruction applies strict pointing requirements which limit sensitivity to charged particles originating far from the primary interaction point. To recover efficiency for LLPs decaying within the tracking detector volume, the ATLAS Collaboration employs a dedicated large-radius tracking (LRT) passwith loosened pointing requirements. During Run 2 of the LHC, the LRT implementation produced many incorrectly reconstructed tracks and was therefore only deployed in small subsets of events. In preparation for LHC Run 3, ATLAS has significantly improved both standard and large-radius track reconstruction performance, allowing for LRT to run in all events. This development greatly expands the potential phase-space of LLP searches and streamlines LLP analysis workflows. This paper will highlight the above achievement and report on the readiness of the ATLAS detector for track-based LLP searches in Run 3.Öğe Measurement of the Centrality Dependence of the Dijet Yield in p plus Pb Collisions at ?sNN=8.16 TeV with the ATLAS Detector(Amer Physical Soc, 2024) Aad, G.; Abbott, B.; Abeling, K.; Abicht, N. J.; Abidi, S. H.; Aboulhorma, A.; Çetin, Serkant AliATLAS measured the centrality dependence of the dijet yield using 165 nb-1 of p + Pb data collected at p 1/4 8.16 TeV in 2016. The event centrality, which reflects the p + Pb impact parameter, is ffiffiffiffiffiffiffi sNN characterized by the total transverse energy registered in the Pb-going side of the forward calorimeter. The central-to-peripheral ratio of the scaled dijet yields, RCP, is evaluated, and the results are presented as a function of variables that reflect the kinematics of the initial hard parton scattering process. The RCP shows a scaling with the Bjorken x of the parton originating from the proton, xp, while no such trend is observed as a function of xPb. This analysis provides unique input to understanding the role of small proton spatial configurations in p + Pb collisions by covering parton momentum fractions from the valence region down to xp similar to 10-3 and xPb similar to 4 x 10-4.Öğe Search for single production of vector-like T quarks decaying into Ht or Zt in pp collisions at ?s=13 TeV with the ATLAS detector(Springer, 2023) Aad, G.; Abbott, B.; Abeling, K.; Abidi, S. H.; Aboulhorma, A.; Abramowicz, H.; Çetin, Serkant AliThis paper describes a search for the single production of an up-type vector-like quark (T) decaying as T -> Ht or T -> Zt. The search utilises a dataset of pp collisions at root s = 13 TeV collected with the ATLAS detector during the 2015-2018 data-taking period of the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb(-1). Data are analysed in final states containing a single lepton with multiple jets and b-jets. The presence of boosted heavy resonances in the event is exploited to discriminate the signal from the Standard Model background. No significant excess above the Standard Model expectation is observed, and 95% CL upper limits are set on the production cross section of T quarks in different decay channels. The results are interpreted in several benchmark scenarios to set limits on the mass and universal coupling strength (kappa) of the vector-like quark. For singlet T quarks, kappa values above 0.53 are excluded for all masses below 2.3 TeV. At a mass of 1.6 TeV, kappa values as low as 0.35 are excluded. For T quarks in the doublet scenario, where the production cross section is much lower, kappa values above 0.72 are excluded for all masses below 1.7 TeV, and this exclusion is extended to kappa above 0.55 for low masses around 1.0 TeV.Öğe Search for direct production of electroweakinos in final states with one lepton, jets and missing transverse momentum in pp collisions at ?s=13 TeV with the ATLAS detector(Springer, 2023) Aad, G.; Abbott, B.; Abeling, K.; Abicht, N. J.; Abidi, S. H.; Aboulhorma, A.; Çetin, Serkant AliSearches for electroweak production of wino-like chargino pairs, (chi) over tilde (+)(1)(chi) over tilde (-), 1, and of wino-like chargino and next-to-lightest neutralino, (chi) over tilde (+/-)(1)(chi) over tilde (0)(2), are presented. The models explored assume that the charginos decay into a W boson and the lightest neutralino, (chi) over tilde chi(+/-)(1) -> W-+/- (chi) over tilde (0)(1) The next-to-lightest neutralinos are degenerate in mass with the chargino and decay to (chi) over tilde (0)(1) and either a Z or a Higgs boson, (chi) over tilde (0)(2) -> Z (chi) over tildeX(1)(0) or h (chi) over tilde (0)(1). The searches exploit the presence of a single isolated lepton and missing transverse momentum from the W boson decay products and the lightest neutralinos, and the presence of jets from hadronically decaying Z or W bosons or from the Higgs boson decaying into a pair of b-quarks. The searches use 139 fb(-1) of root s = 13TeV proton-proton collisions data collected by the ATLAS detector at the Large Hadron Collider between 2015 and 2018. No deviations from the Standard Model expectations are found, and 95% confidence level exclusion limits are set. Chargino masses ranging from 260 to 520 GeV are excluded for a massless (chi) over tilde (1)(0) in chargino pair production models. Degenerate chargino and next-to-lightest neutralino masses ranging from 260 to 420 GeV are excluded for a massless (chi) over tilde (1)(0) for (chi) over tilde (0)(2) -> Z (chi) over tilde (0)(1). For decays through an on-shell Higgs boson and for mass-splitting between (chi) over tilde (+/-)(1)/(chi) over tilde (0)(2) and (chi) over tilde (0)(1) as small as the Higgs boson mass, mass limits are improved by up to 40 GeV in the range of 200-260 GeV and 280-470 GeV compared to previous ATLAS constraints.Öğe Search for direct production of winos and higgsinos in events with two same-charge leptons or three leptons in pp collision data at ?s=13 TeV with the ATLAS detector(Springer, 2023) Aad, G.; Abbott, B.; Abbott, D. C.; Abeling, K.; Abidi, S. H.; Aboulhorma, A.; Çetin, Serkant AliA search for supersymmetry targeting the direct production of winos and higgsinos is conducted in final states with either two leptons (e or mu) with the same electric charge, or three leptons. The analysis uses 139 fb(-1) of pp collision data at root s = 13TeV collected with the ATLAS detector during Run 2 of the Large Hadron Collider. No significant excess over the Standard Model expectation is observed. Simplified and complete models with and without R-parity conservation are considered. In topologies with intermediate states including either Wh or WZ pairs, wino masses up to 525 GeV and 250 GeV are excluded, respectively, for a bino of vanishing mass. Higgsino masses smaller than 440 GeV are excluded in a natural R-parity-violating model with bilinear terms. Upper limits on the production cross section of generic events beyond the Standard Model as low as 40 ab are obtained in signal regions optimised for these models and also for an R-parity-violating scenario with baryon-number-violating higgsino decays into top quarks and jets. The analysis significantly improves sensitivity to supersymmetric models and other processes beyond the Standard Model that may contribute to the considered final states.Öğe Measurements of multijet event isotropies using optimal transport with the ATLAS detector(Springer, 2023) Aad, G.; Abbott, B.; Abeling, K.; Abicht, N. J.; Abidi, S. H.; Aboulhorma, A.; Çetin, Serkant AliA measurement of novel event shapes quantifying the isotropy of collider events is performed in 140 fb(-1) of proton-proton collisions with root s = 13TeV centre-of-mass energy recorded with the ATLAS detector at CERN's Large Hadron Collider. These event shapes are defined as the Wasserstein distance between collider events and isotropic reference geometries. This distance is evaluated by solving optimal transport problems, using the 'Energy-Mover's Distance'. Isotropic references with cylindrical and circular symmetries are studied, to probe the symmetries of interest at hadron colliders. The novel event-shape observables defined in this way are infrared- and collinear-safe, have improved dynamic range and have greater sensitivity to isotropic radiation patterns than other event shapes. The measured event-shape variables are corrected for detector effects, and presented in inclusive bins of jet multiplicity and the scalar sum of the two leading jets' transverse momenta. The measured distributions are provided as inputs to future Monte Carlo tuning campaigns and other studies probing fundamental properties of QCD and the production of hadronic final states up to the TeV-scale.Öğe Studies of new Higgs boson interactions through nonresonant HH production in the b(b)over-bar?? final state in pp collisions at ?s=13 TeV with the ATLAS detector(Springer, 2024) Aad, G.; Abbott, B.; Abeling, K.; Abicht, N. J.; Abidi, S. H.; Aboulhorma, A.; Çetin, Serkant AliA search for nonresonant Higgs boson pair production in the b (b) over bar gamma gamma final state is performed using 140 fb(-1) of proton-proton collisions at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. This analysis supersedes and expands upon the previous nonresonant ATLAS results in this final state based on the same data sample. The analysis strategy is optimised to probe anomalous values not only of the Higgs (H) boson self-coupling modifier kappa(lambda) but also of the quartic HHVV (V = W, Z) coupling modifier kappa(2V). No significant excess above the expected background from Standard Model processes is observed. An observed upper limit mu(HH) < 4.0 is set at 95% confidence level on the Higgs boson pair production cross-section normalised to its Standard Model prediction. The 95% confidence intervals for the coupling modifiers are -1.4 < kappa(lambda) < 6.9 and -0.5 < kappa(2V) < 2.7, assuming all other Higgs boson couplings except the one under study are fixed to the Standard Model predictions. The results are interpreted in the Standard Model effective field theory and Higgs effective field theory frameworks in terms of constraints on the couplings of anomalous Higgs boson (self-)interactions.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 Search for a new heavy scalar particle decaying into a Higgs boson and a new scalar singlet in final states with one or two light leptons and a pair of ?-leptons with the ATLAS detector(Springer, 2023) Aad, G.; Abbott, B.; Abeling, K.; Abicht, N. J.; Abidi, S. H.; Aboulhorma, A.; Çetin, Serkant AliA search for a new heavy scalar particle X decaying into a Standard Model (SM) Higgs boson and a new singlet scalar particle S is presented. The search uses a proton-proton (pp) collision data sample with an integrated luminosity of 140 fb(-1) recorded at a centre-of-mass energy of root s = 13 TeV with the ATLAS detector at the Large Hadron Collider. The most sensitive mass parameter space is explored in X mass ranging from 500 to 1500 GeV, with the corresponding S mass in the range 200-500 GeV. The search selects events with two hadronically decaying tau-lepton candidates from H -> tau(+)tau(-) decays and one or two light leptons (l = e, mu) from S -> VV (V = W, Z) decays while the remaining V boson decays hadronically or to neutrinos. A multivariate discriminant based on event kinematics is used to separate the signal from the background. No excess is observed beyond the expected SM background and 95% confidence level upper limits between 72 fb and 542 fb are derived on the cross-section sigma(pp -> X -> SH) assuming the same SM-Higgs boson-like decay branching ratios for the S -> VV decay. Upper limits on the visible cross-sections sigma(pp -> X -> SH -> WW tau tau) and sigma(pp -> X -> SH -> ZZ tau tau) are also set in the ranges 3-26 fb and 6-33 fb, respectively.Öğe Differential cross-section measurements of the production of four charged leptons in association with two jets using the ATLAS detector(Springer, 2024) Aad, G.; Abbott, B.; Abeling, K.; Abicht, N. J.; Abidi, S. H.; Aboulhorma, A.; Çetin, Serkant AliDifferential cross-sections are measured for the production of four charged leptons in association with two jets. These measurements are sensitive to final states in which the jets are produced via the strong interaction as well as to the purely-electroweak vector boson scattering process. The analysis is performed using proton-proton collision data collected by ATLAS at root s = 13TeV and with an integrated luminosity of 140 fb(-1). The data are corrected for the effects of detector inefficiency and resolution and are compared to stateof-the-art Monte Carlo event generator predictions. The differential cross-sections are used to search for anomalous weak-boson self-interactions that are induced by dimension-six and dimension-eight operators in Standard Model effective field theory.Öğe Search for flavour-changing neutral tqH interactions with H ? ?? in pp collisions at ?s=13 TeV using the ATLAS detector(Springer, 2023) Aad, G.; Abbott, B.; Abeling, K.; Abicht, N. J.; Abidi, S. H.; Aboulhorma, A.; Çetin, Serkant AliA search for flavour-changing neutral interactions involving the top quark, the Higgs boson and an up-type quark q ( q = c, u) is presented. The proton-proton collision data set used, with an integrated luminosity of 139 fb(-1), was collected at root s = 13TeV by the ATLAS experiment at the Large Hadron Collider. Both the decay process t -> qH in tt production and the production process pp. tH, with the Higgs boson decaying into two photons, are investigated. No significant excess is observed and upper limits are set on the t. cH and the t. uH branching ratios of 4.3x10(-4) and 3.8x10(-4), respectively, at the 95% confidence level, while the expected limits in the absence of signal are 4.7x10(-4) and 3.9x10(-4). Combining this search with ATLAS searches in the H. t+ t- and H. b b final states yields observed (expected) upper limits on the t -> cH branching ratio of 5.8 x 10(-4) (3.0 x 10(-4)) at the 95% confidence level. The corresponding observed (expected) upper limit on the t -> uH branching ratio is 4.0 x 10(-4) (2.4 x 10(-4)).Öğe Search for vector-boson resonances decaying into a top quark and a bottom quark using pp collisions at ?s=13 TeV with the ATLAS detector(Springer, 2023) Aad, G.; Abbott, B.; Abeling, K.; Abicht, N. J.; Abidi, S. H.; Aboulhorma, A.; Çetin, Serkant AliA search for a new massive charged gauge boson, W ', is performed with the ATLAS detector at the LHC. The dataset used in this analysis was collected from proton-proton collisions at a centre-of-mass energy of root s = 13 TeV, and corresponds to an integrated luminosity of 139 fb(-1). The reconstructed tb invariant mass is used to search for a W ' boson decaying into a top quark and a bottom quark. The result is interpreted in terms of a W ' boson with purely right-handed or left-handed chirality in a mass range of 0.5-6 TeV. Different values for the coupling of the W ' boson to the top and bottom quarks are considered, taking into account interference with single-top-quark production in the s-channel. No significant deviation from the background prediction is observed. The results are expressed as upper limits on the W ' -> tb production cross-section times branching ratio as a function of the W '-boson mass and in the plane of the coupling vs the W '-boson mass.Öğe Search for heavy Higgs bosons with flavour-violating couplings in multi-lepton plus b-jets final states in pp collisions at 13 TeV with the ATLAS detector(Springer, 2023) Aad, G.; Abbott, B.; Abeling, K.; Abicht, N. J.; Abidi, S. H.; Aboulhorma, A.; Çetin, Serkant AliA search for new heavy scalars with flavour-violating decays in final states with multiple leptons and b-tagged jets is presented. The results are interpreted in terms of a general two-Higgs-doublet model involving an additional scalar with couplings to the top-quark and the three up-type quarks (rho(tt),rho(tc), and rho(tu)). The targeted signals lead to final states with either a same-sign top-quark pair, three top-quarks, or four top-quarks. The search is based on a data sample of proton-proton collisions at root s = 13TeV recorded with the ATLAS detector during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb(-1). Events are categorised depending on the multiplicity of light charged leptons (electrons or muons), total lepton charge, and a deep-neural-network output to enhance the purity of each of the signals. Masses of an additional scalar boson mH between 200- 630 GeV with couplings rho(tt) = 0.4, rho(tc) = 0.2, and rho(tu) = 0.2 are excluded at 95% confidence level. Additional interpretations are provided in models of R-parity violating supersymmetry, motivated by the recent flavour and ( g - 2) (mu) anomalies.Öğe Measurement of the B0s ? ?? effective lifetime with the ATLAS detector(Springer, 2023) Aad, G.; Abbott, B.; Abeling, K.; Abicht, N. J.; Abidi, S. H.; Aboulhorma, A.; Çetin, Serkant AliThis paper reports the first ATLAS measurement of the B-s(0) -> mu mu effective lifetime. The measurement is based on the data collected in 2015-2016, amounting to 26.3 fb(-1) of 13TeV LHC proton-proton collisions. The proper decay-time distribution of 58 +/- 13 background-subtracted signal candidates is fit with simulated signal templates parameterised as a function of the B-s(0) effective lifetime, with statistical uncertainties extracted through a Neyman construction. The resulting effective measurement of the B-s(0) -> mu mu lifetime is 0.99(-0.07)(+0.42) (stat.) +/- 0.17 (syst.) ps and it is found to be consistent with the Standard Model.Öğe Measurement of the production cross-section of J/? and ?(2S) mesons in pp collisions at s=13 TeV with the ATLAS detector(Springer Nature, 2024) Aad, G.; Abbott, B.; Abeling, K.; Abicht, N.J.; Abidi, S.H.; Aboulhorma, A.; Çetin, Serkant AliMeasurements of the differential production cross-sections of prompt and non-prompt J/? and ?(2S) mesons with transverse momenta between 8 and 360 GeV and rapidity in the range |y|<2 are reported. Furthermore, measurements of the non-prompt fractions of J/? and ?(2S), and the prompt and non-prompt ?(2S)-to-J/? production ratios, are presented. The analysis is performed using 140 fb-1 of s=13 TeV pp collision data recorded by the ATLAS detector at the LHC during the years 2015–2018. © The Author(s) 2024.Öğe Search for pair production of third-generation leptoquarks decaying into a bottom quark and a ? -lepton with the ATLAS detector(Institute for Ionics, 2023) Aad, G.; Abbott, B.; Abeling, K.; Abidi, S.H.; Aboulhorma, A.; Abramowicz, H.; Çetin, Serkant AliA search for pair-produced scalar or vector leptoquarks decaying into a b-quark and a ? -lepton is presented using the full LHC Run 2 (2015–2018) data sample of 139 fb - 1 collected with the ATLAS detector in proton–proton collisions at a centre-of-mass energy of s=13 TeV. Events in which at least one ? -lepton decays hadronically are considered, and multivariate discriminants are used to extract the signals. No significant deviations from the Standard Model expectation are observed and 95% confidence-level upper limits on the production cross-section are derived as a function of leptoquark mass and branching ratio B into a ? -lepton and b-quark. For scalar leptoquarks, masses below 1460 GeV are excluded assuming B= 100 %, while for vector leptoquarks the corresponding limit is 1650 GeV (1910 GeV) in the minimal-coupling (Yang–Mills) scenario. © 2023, The Author(s).Öğe Measurement of exclusive pion pair production in proton–proton collisions at ?s=7TeV with the ATLAS detector(Institute for Ionics, 2023) Aad, G.; Abbott, B.; Abbott, D.C.; Abeling, K.; Abidi, S.H.; Aboulhorma, A.; Çetin, Serkant AliThe exclusive production of pion pairs in the process pp? pp?+?- has been measured at s=7TeV with the ATLAS detector at the LHC, using 80?b-1 of low-luminosity data. The pion pairs were detected in the ATLAS central detector while outgoing protons were measured in the forward ATLAS ALFA detector system. This represents the first use of proton tagging to measure an exclusive hadronic final state at the LHC. A cross-section measurement is performed in two kinematic regions defined by the proton momenta, the pion rapidities and transverse momenta, and the pion–pion invariant mass. Cross-section values of 4.8±1.0(stat)-0.2+0.3(syst)?b and 9±6(stat)-2+2(syst)?b are obtained in the two regions; they are compared with theoretical models and provide a demonstration of the feasibility of measurements of this type. © 2023, The Author(s).
