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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 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 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).Öğe Luminosity determination in pp collisions at ?s=13 TeV using the ATLAS detector at the LHC(Institute for Ionics, 2023) Aad, G.; Abbott, B.; Abeling, K.; Abidi, S.H.; Aboulhorma, A.; Abramowicz, H.; Çetin, Serkant AliThe luminosity determination for the ATLAS detector at the LHC during Run 2 is presented, with pp collisions at a centre-of-mass energy s=13 TeV. The absolute luminosity scale is determined using van der Meer beam separation scans during dedicated running periods in each year, and extrapolated to the physics data-taking regime using complementary measurements from several luminosity-sensitive detectors. The total uncertainties in the integrated luminosity for each individual year of data-taking range from 0.9% to 1.1%, and are partially correlated between years. After standard data-quality selections, the full Run 2 pp data sample corresponds to an integrated luminosity of 140.1 ± 1.2 fb - 1 , i.e. an uncertainty of 0.83%. A dedicated sample of low-pileup data recorded in 2017–2018 for precision Standard Model physics measurements is analysed separately, and has an integrated luminosity of 338.1 ± 3.1 pb - 1 . © 2023, The Author(s).Öğe Evidence for the Higgs boson decay to a Z boson and a photon at the LHC(American Physical Society, 2024) Aad, G.; Abbott, B.; Abeling, K.; Abicht, N.J.; Abidi, S.H.; Aboulhorma, A.; Çetin, Serkant AliThe first evidence for the Higgs boson decay to a Formula Presented boson and a photon is presented, with a statistical significance of 3.4 standard deviations. The result is derived from a combined analysis of the searches performed by the ATLAS and CMS Collaborations with proton-proton collision datasets collected at the CERN Large Hadron Collider (LHC) from 2015 to 2018. These correspond to integrated luminosities of around Formula Presented for each experiment, at a center-of-mass energy of 13 TeV. The measured signal yield is Formula Presented times the standard model prediction, and agrees with the theoretical expectation within 1.9 standard deviations. © 2024 CERN, for the ATLAS and CMSs Collaboration.Öğe Observation of D+ ? KS0 a0 (980)+ in the Amplitude Analysis of D+ ? KS0 ?+?(American Physical Society, 2024) Ablikim, M.; Achasov, M.N.; Adlarson, P.; Ai, X.C.; Aliberti, R.; Amoroso, A.; Çetin, Serkant AliWe perform for the first time an amplitude analysis of the decay D+?KS0?+? and report the observation of the decay D+?KS0a0(980)+ using 2.93 fb-1 of e+e- collision data taken at a center-of-mass energy of 3.773 GeV with the BESIII detector. As the only W-annihilation-free decay among D to a0(980) pseudoscalar, D+?KS0a0(980)+ is the ideal decay in extracting the contributions of the W-emission amplitudes involving a0(980) and to study the final-state interactions. The absolute branching fraction of D+?KS0?+? is measured to be (1.27±0.04stat±0.03syst)%. The branching fractions of intermediate processes D+?KS0a0(980)+ with a0(980)+??+? and D+??+K?0?(1430)0 with K?0?(1430)0?KS0? are measured to be (1.33±0.05stat±0.04syst)% and (0.14±0.03stat±0.01syst)%, respectively. © 2024 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "https://creativecommons.org/licenses/by/4.0/"Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.Öğe Search for displaced photons produced in exotic decays of the Higgs boson using 13 TeV pp collisions with the ATLAS detector(American Physical Society, 2023) Filmer, E.K.; Jackson, P.; Kong, A.X.Y.; Potti, H.; Ruggeri, T.A.; Ting, E.X.L.; Çetin, Serkant AliA search is performed for delayed and nonpointing photons originating from the displaced decay of a neutral long-lived particle (LLP). The analysis uses the full run 2 dataset of proton-proton collisions delivered by the LHC at a center-of-mass energy of Formula Presented between 2015 and 2018 and recorded by the ATLAS detector, corresponding to an integrated luminosity of Formula Presented. The capabilities of the ATLAS electromagnetic calorimeter are exploited to precisely measure the arrival times and trajectories of photons. The results are interpreted in a scenario where the LLPs are pair produced in exotic decays of the 125 GeV Higgs boson, and each LLP subsequently decays into a photon and a particle that escapes direct detection, giving rise to missing transverse momentum. No significant excess is observed above the expectation due to Standard Model background processes. The results are used to set upper limits on the branching ratio of the exotic decay of the Higgs boson. A model-independent limit is also set on the production of photons with large values of displacement and time delay. © 2023 CERN, for the ATLAS Collaboration.Öğe Observation of W?? triboson production in proton-proton collisions at s=13 TeV with the ATLAS detector(Elsevier B.V., 2024) Aad, G.; Abbott, B.; Abeling, K.; Abicht, N.J.; Abidi, S.H.; Aboulhorma, A.; Çetin, Serkant AliThis letter reports the observation of W(??)?? production in proton-proton collisions. This measurement uses the full Run 2 sample of events recorded at a center-of-mass energy of s=13 TeV by the ATLAS detector at the LHC, corresponding to an integrated luminosity of 140 fb?1. Events with a leptonically-decaying W boson and at least two photons are considered. The background-only hypothesis is rejected with an observed and expected significance of 5.6 standard deviations. The inclusive fiducial production cross section of W(e?)?? and W(??)?? events is measured to be ?fid=13.8±1.1(stat)+2.1?2.0(syst)±0.1(lumi) fb, in agreement with the Standard Model prediction. © 2023 The Author(s)Öğe Inclusive and differential cross-sections for dilepton tt¯ production measured in ?s = 13 TeV pp collisions with the ATLAS detector(Springer Science and Business Media Deutschland GmbH, 2023) Aad, G.; Abbott, B.; Abbott, D.C.; Abeling, K.; Abidi, S.H.; Aboulhorma, A.; Çetin, Serkant AliDifferential and double-differential distributions of kinematic variables of leptons from decays of top-quark pairs (tt¯) are measured using the full LHC Run 2 data sample collected with the ATLAS detector. The data were collected at a pp collision energy of s = 13 TeV and correspond to an integrated luminosity of 140 fb?1. The measurements use events containing an oppositely charged e? pair and b-tagged jets. The results are compared with predictions from several Monte Carlo generators. While no prediction is found to be consistent with all distributions, a better agreement with measurements of the lepton p T distributions is obtained by reweighting the tt¯ sample so as to reproduce the top-quark p T distribution from an NNLO calculation. The inclusive top-quark pair production cross-section is measured as well, both in a fiducial region and in the full phase-space. The total inclusive cross-section is found to be ?tt¯=829±1(stat)±13(syst)±8(lumi)±2(beam)pb, where the uncertainties are due to statistics, systematic effects, the integrated luminosity and the beam energy. This is in excellent agreement with the theoretical expectation. [Figure not available: see fulltext.] © 2023, The Author(s).Öğe Search for direct pair production of sleptons and charginos decaying to two leptons and neutralinos with mass splittings near the W-boson mass in ?s = 13 TeV pp collisions with the ATLAS detector(Springer Science and Business Media Deutschland GmbH, 2023) Aad, G.; Abbott, B.; Abbott, D.C.; Abeling, K.; Abidi, S.H.; Aboulhorma, A.; Çetin, Serkant AliA search for the electroweak production of pairs of charged sleptons or charginos decaying into two-lepton final states with missing transverse momentum is presented. Two simplified models of R-parity-conserving supersymmetry are considered: direct pair-production of sleptons (?~ ?~) , with each decaying into a charged lepton and a ?~10 neutralino, and direct pair-production of the lightest charginos (?~1±?~1?) , with each decaying into a W-boson and a ?~10 . The lightest neutralino (?~10) is assumed to be the lightest supersymmetric particle (LSP). The analyses target the experimentally challenging mass regions where m(?~)?m(?~10) and m(?~1±)?m(?~10) are close to the W-boson mass (‘moderately compressed’ regions). The search uses 139 fb?1 of s = 13 TeV proton-proton collisions recorded by the ATLAS detector at the Large Hadron Collider. No significant excesses over the expected background are observed. Exclusion limits on the simplified models under study are reported in the (?~?~10) and (?~1±?~10) mass planes at 95% confidence level (CL). Sleptons with masses up to 150 GeV are excluded at 95% CL for the case of a mass-splitting between sleptons and the LSP of 50 GeV. Chargino masses up to 140 GeV are excluded at 95% CL for the case of a mass-splitting between the chargino and the LSP down to about 100 GeV. [Figure not available: see fulltext.] © 2023, The Author(s).Öğe Search for dark photons from Higgs boson decays via ZH production with a photon plus missing transverse momentum signature from pp collisions at ?s = 13 TeV with the ATLAS detector(Springer Science and Business Media Deutschland GmbH, 2023) Aad, G.; Abbott, B.; Abbott, D.C.; Abeling, K.; Abidi, S.H.; Aboulhorma, A.; Çetin, Serkant AliThis paper describes a search for dark photons (?d) in proton-proton collisions at s = 13 TeV at the Large Hadron Collider (LHC). The dark photons are searched for in the decay of Higgs bosons (H ? ??d) produced through the ZH production mode. The transverse mass of the system, made of the photon and the missing transverse momentum from the non-interacting ?d, presents a distinctive signature as it peaks near the Higgs boson mass. The results presented use the total Run-2 integrated luminosity of 139 fb?1 recorded by the ATLAS detector at the LHC. The dominant reducible background processes are estimated using data-driven techniques. A Boosted Decision Tree technique is adopted to enhance the sensitivity of the search. As no excess is observed with respect to the Standard Model prediction, an observed (expected) upper limit on the branching ratio BR(H ? ??d) of 2.28% (2.82?0.84+1.33%) is set at 95% CL for massless ?d. For massive dark photons up to 40 GeV, the observed (expected) upper limits on BR(H ? ??d) at 95% confidence level is found within the [2.19,2.52]% ([2.71,3.11]%) range. [Figure not available: see fulltext.] © 2023, The Author(s).Öğe Search for a new scalar resonance in flavour-changing neutral-current top-quark decays t ? qX (q = u, c), with X ? bb¯ , in proton-proton collisions at ?s = 13 TeV with the ATLAS detector(Springer Science and Business Media Deutschland GmbH, 2023) Aad, G.; Abbott, B.; Abbott, D.C.; Abeling, K.; Abidi, S.H.; Aboulhorma, A.; Çetin, Serkant AliA search for flavour-changing neutral-current decays of a top quark into an up-type quark (either up or charm) and a light scalar particle X decaying into a bottom anti-bottom quark pair is presented. The search focuses on top-quark pair production where one top quark decays to qX, with X ? bb¯ , and the other top quark decays according to the Standard Model, with the W boson decaying leptonically. The final state is thus characterised by an isolated electron or muon and at least four jets. Events are categorised according to the multiplicity of jets and jets tagged as originating from b-quarks, and a neural network is used to discriminate between signal and background processes. The data analysed correspond to 139 fb?1 of proton–proton collisions at a centre-of-mass energy of 13 TeV, recorded with the ATLAS detector at the LHC. The 95% confidence-level upper limits between 0.019% and 0.062% are derived for the branching fraction B (t ? uX) and between 0.018% and 0.078% for the branching fraction B (t ? cX), for masses of the scalar particle X between 20 and 160 GeV. [Figure not available: see fulltext.] © 2023, The Author(s).Öğe Search for pair production of squarks or gluinos decaying via sleptons or weak bosons in final states with two same-sign or three leptons with the ATLAS detector(Springer Science and Business Media Deutschland GmbH, 2024) Aad, G.; Abbott, B.; Abeling, K.; Abicht, N.J.; Abidi, S.H.; Aboulhorma, A.; Çetin, Serkant AliA search for pair production of squarks or gluinos decaying via sleptons or weak bosons is reported. The search targets a final state with exactly two leptons with same-sign electric charge or at least three leptons without any charge requirement. The analysed data set corresponds to an integrated luminosity of 139 fb?1 of proton-proton collisions collected at a centre-of-mass energy of 13 TeV with the ATLAS detector at the LHC. Multiple signal regions are defined, targeting several SUSY simplified models yielding the desired final states. A single control region is used to constrain the normalisation of the WZ + jets background. No significant excess of events over the Standard Model expectation is observed. The results are interpreted in the context of several supersymmetric models featuring R-parity conservation or R-parity violation, yielding exclusion limits surpassing those from previous searches. In models considering gluino (squark) pair production, gluino (squark) masses up to 2.2 (1.7) TeV are excluded at 95% confidence level. © The Author(s) 2024.Öğe Observation of chi(cJ) -> lambda(lambda)over-bar(eta)(PHYSICAL REVIEW D, 2022) Ablikim, M.; Achasov, M. N.; Adlarson, P.; Albrecht, M.; Aliberti, R.; Çetin, Serkant Ali; Kolcu, Onur BuğraBy analyzing (448.1 +/- 2.9) x 10(6) psi(3686) events collected with the BESIII detector operating at the BEPCII collider, the decays of chi(cJ) -> Lambda(Lambda) over bar (eta) (J = 0, 1, and 2) are observed for the first time with statistical significances of 13.9 sigma, 6.7 sigma, and 8.2 sigma, respectively. The product branching fractions of psi(3686) -> gamma chi(cJ) and chi(cJ) -> Lambda(Lambda) over bar (eta) are measured. Dividing by the world averages of the branching fractions of psi(3686) -> gamma chi(cJ), the branching fractions of chi(cJ) -> Lambda(Lambda) over bar (eta) decays are determined to be (2.31 +/- 0.30 +/- 0.21) x 10(-4), (5.86 +/- 1.38 +/- 0.68) x 10(-5), and (1.05 +/- 0.21 +/- 0.15) x 10(-4) for J = 0, 1 and 2, respectively, where the first uncertainties are statistical and the second systematic.Öğe Absolute measurements of branching fractions of Cabibbo-suppressed hadronic D0(+) decays involving multiple pions(AMER PHYSICAL SOC, 2022) Ablikim, M.; Achasov, M. N.; Adlarson, Patrik; Albrecht, Malte; Aliberti, Riccardo; Çetin, Serkant Ali; Kolcu, Onur BuğraBy analyzing e(+)e(-) annihilation data with an integrated luminosity of 2.93 fb(-1) collected at the center-of-mass energy root s = 3.773 GeV with the BESIII detector, we present the first absolute measurements of the branching fractions of twenty Cabibbo-suppressed hadronic D0(+) decays involving multiple pions. The highest four branching fractions obtained are B(D-0 -> pi(+)pi(-)pi(0)) = (1.343 +/- 0.013(stat) +/- 0.016(syst))%, B(D-0 -> pi(+)pi(-)2 pi(0)) = (1.002 +/- 0.019(stat )+/- 0.024(syst))%, B(D-0 -> 2 pi(+)pi(-)pi(0))=(1.165 +/- 0.021(stat) +/- 0.021(sy)(st))%, and B(D+ -> 2 pi(+)pi(-)pi(0)). (1.074 +/- 0.040(stat) 0.030(syst))%. The CP asymmetries for the six decays with highest signal yields are also determined and found to be compatible with zero.Öğe Observation of the decay ?(3686) ? ? ?? ¯ + and measurement of its angular distribution(Springer link, 2022) Ablikim M.; Achasov M.N.; Adlarson P.; Albrecht M.; Aliberti R.; Amoroso A.; An M.R.; An Q.; Bai X.H.; Bai Y.; Bakina O.; Baldini Ferroli R.; Çetin, Serkant Ali; Kolcu, Onur BuğraUsing (448.1 ± 2.9) × 106?(3686) events collected with the BESIII detector at the BEPCII collider, the decay ?(3686) ?? ?? ¯ + is observed for the first time with a branching fraction of (2.82 ± 0.04stat.± 0.08syst.) × 10?4, and the angular parameter ??? is measured to be 0.96 ± 0.09stat.± 0.03syst.. [Figure not available: see fulltext.] © 2022, The Author(s).Öğe Measurement of the absolute branching fraction and decay asymmetry of ??n?(American Physical Society, 2022) Ablikim, M; Achasov, M. N.; Adlarson, Patrik; Albrecht, Malte; Amoroso A.; Çetin, Serkant Ali; Kolcu, Onur BuğraThe radiative hyperon decay ??n? is studied using (10087±44)×10^{6} J/? events collected with the BESIII detector operating at BEPCII. The absolute branching fraction of the decay ??n? is determined to be (0.832±0.038_{stat}±0.054_{syst})×10^{-3}, which is a factor of 2.1 lower and 5.6 standard deviations different than the previous measurement. By analyzing the joint angular distribution of the decay products, the first determination of the decay asymmetry ?_{?} is reported with a value of -0.16±0.10_{stat}±0.05_{syst}.Öğe Measurement of the branching fraction of the singly cabibbo-suppressed decay ?c+ ? ?k+(APS, 2022) Ablikim M.; Achasov M.N.; Baldini Ferroli R.; Balossino I.; Bertani M.; Kolcu, Onur Buğra; Çetin, Serkant AliWe report a branching fraction measurement of the singly Cabibbo-suppressed decay ?c+??K+ using a data sample collected with the BESIII detector at the BEPCII storage ring. The data span center-of-mass energies from 4.599 to 4.950 GeV and correspond to an integrated luminosity of 6.44 fb-1. The branching fraction of ?c+??K+ relative to that of the Cabibbo-favored decay ?c+???+ is measured to be R=B(?c+??K+)B(?c+???+)=(4.78±0.34±0.20)%. Combining with the world-average value of B(?c+???+), we obtain B(?c+??K+)=(6.21±0.44±0.26±0.34)×10-4. Here the first uncertainties are statistical, the second systematic, and the third comes from the uncertainty of the ?c+???+ branching fraction. This result, which is more precise than previous measurements, does not agree with theoretical predictions, and suggests that nonfactorizable contributions have been underestimated in current models. © 2022 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "https://creativecommons.org/licenses/by/4.0/"Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.Öğe Improved measurement of the strong-phase difference delta(K pi )(D)in quantum-correlated D(D)over-bar decays( )(SPRINGER, 2022) Ablikim, M; Achasov, M. N; Adlarson, P.; Albrecht, Malte; Aliberti, R.; Çetin, Serkant Ali; Kolcu, Onur BuğraThe decay D -> K-pi(+) is studied in a sample of quantum-correlated D (D) over bar pairs, based on a data set corresponding to an integrated luminosity of 2.93 fb(-1) collected at the psi(3770) resonance by the BESIII experiment. The asym- metry between CP-odd and CP-even eigenstate decays into K-pi(+) is determined to be A(K pi) = 0.132 +/- 0.011 +/- 0.007, where the first uncertainty is statistical and the second is systematic. This measurement is an update of an earlier study exploiting additional tagging modes, including several decay modes involving a K-L(0) meson. The branching fractions of the K-L(0) modes are determined as input to the analysis in a manner that is independent of any strong phase uncertainty. Using the predominantly CP-even tag D -> pi(+)pi(-)pi(0) and the ensemble of CP-odd eigenstate tags, the observable A(K pi)(pi pi pi 0) is measured to be 0.130 +/- 0.012 +/- 0.008. The two asymmetries are sensitive to r(D)(K pi) delta(K)(pi)(D), where r(D)(K pi) and S-D(K pi) are the ratio of amplitudes and phase difference, respectively, between the doubly Cabibbo-suppressed and Cabibbofavoured decays. In addition, events containing D -> K-pi(+) tagged by D -> K-S,L(0) pi(+)pi(-) are studied in bins of phase space of the three-body decays. This analysis has sensitivity to both r(D)(K pi) cos delta(K)(pi)(D) and r(D)(K pi) sin delta(K)(pi)(D). A fit to A(K pi), A(K pi)(pi pi pi 0) and the phase-space distribution of the D -> K-S,L(0) pi(+)pi(-) tags yields delta(K)(pi)(D) = (187.6(-9.7-6.4)(+8.9+5.4))degrees , where external con- straints are applied for r(D)(K pi) and other relevant parameters. This is the most precise measurement of delta(K)(pi)(D) in quantumcorrelated D (D) over bar decays.
