Examinando por Autor "Abouzeid, O.S."
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Ítem Dijet Resonance Search with Weak Supervision Using s =13 TeV pp Collisions in the ATLAS Detector(American Physical Society, 2020-09) Aad, G.; Abbott, B.; Abbott, D.C.; Abed Abud, A.; Abeling, K.; Abhayasinghe, D.K.; Abidi, S.H.; Abouzeid, O.S.; Abraham, N.L.; Abramowicz, H.; Abreu, H.; Abulaiti, Y.This Letter describes a search for narrowly resonant new physics using a machine-learning anomaly detection procedure that does not rely on signal simulations for developing the analysis selection. Weakly supervised learning is used to train classifiers directly on data to enhance potential signals. The targeted topology is dijet events and the features used for machine learning are the masses of the two jets. The resulting analysis is essentially a three-dimensional search A→BC, for mA∼O(TeV), mB,mC∼O(100 GeV) and B, C are reconstructed as large-radius jets, without paying a penalty associated with a large trials factor in the scan of the masses of the two jets. The full run 2 s=13 TeV pp collision dataset of 139 fb-1 recorded by the ATLAS detector at the Large Hadron Collider is used for the search. There is no significant evidence of a localized excess in the dijet invariant mass spectrum between 1.8 and 8.2 TeV. Cross-section limits for narrow-width A, B, and C particles vary with mA, mB, and mC. For example, when mA=3 TeV and mBâ200 GeV, a production cross section between 1 and 5 fb is excluded at 95% confidence level, depending on mC. For certain masses, these limits are up to 10 times more sensitive than those obtained by the inclusive dijet search. These results are complementary to the dedicated searches for the case that B and C are standard model bosons. © 2020 CERN.Ítem Longitudinal Flow Decorrelations in Xe+Xe Collisions at sNN =5.44 TeV with the ATLAS Detector(American Physical Society, 2021-03) Aad, G.; Abbott, B.; Abbott, D.C.; Abed Abud, A.; Abeling, K.; Abhayasinghe, D.K.; Abidi, S.H.; Abouzeid, O.S.; Abraham, N.L.; Abramowicz, H.; Abreu, H.; Abulaiti, Y.; Acharya, B.S.; Achkar, B.; Adachi, S.; Adam, L.; Adam Bourdarios, C.; Adamczyk, L.; Adamek, L.; Adelman, J.; Adersberger, M.; Adiguzel, A.; Adorni, S.The first measurement of longitudinal decorrelations of harmonic flow amplitudes vn for n=2-4 in Xe+Xe collisions at sNN=5.44 TeV is obtained using 3 μb-1 of data with the ATLAS detector at the LHC. The decorrelation signal for v3 and v4 is found to be nearly independent of collision centrality and transverse momentum (pT) requirements on final-state particles, but for v2 a strong centrality and pT dependence is seen. When compared with the results from Pb+Pb collisions at sNN=5.02 TeV, the longitudinal decorrelation signal in midcentral Xe+Xe collisions is found to be larger for v2, but smaller for v3. Current hydrodynamic models reproduce the ratios of the vn measured in Xe+Xe collisions to those in Pb+Pb collisions but fail to describe the magnitudes and trends of the ratios of longitudinal flow decorrelations between Xe+Xe and Pb+Pb. The results on the system-size dependence provide new insights and an important lever arm to separate effects of the longitudinal structure of the initial state from other early and late time effects in heavy-ion collisions. © 2021 CERN.Ítem Performance of the ATLAS muon triggers in Run 2(IOP Publishing Ltd, 2020-09) Aad, G.; Abbott, B.; Abbott, D.C.; Abud, A. Abed; Abeling, K.; Abhayasinghe, D.K.; Abeling, K.; Abhayasinghe, D.K.; Abidi, S.H.; Abouzeid, O.S.; Abraham, N.L.; Abramowicz, H.; Abreu, H.; Abulaiti, Y.; Acharya, B.S.; Achkar, B.; Adam, L.; Bourdarios, C. Adam; Adamczyk, L.; Adamek, L.; Adelman, J.; Adersberger, M.; Adiguzel, A.; Adorni, S.; Adye, T.; Affolder, A.A.; Afik, Y.; Agapopoulou, C.; Agaras, M.N.; Aggarwal, A.; Agheorghiesei, C.; Aguilar-Saavedra, J.A.; Ahmad, A.; Ahmadov, F.; Ahmed, W.S.; Ai, X.; Aielli, G.; Akatsuka, S.; Åkesson, T.P.A.; Akilli, E.; Akimov, A.V.; Khoury, K. Al; Alberghi, G.L.; Albert, J.; Alconada Verzini, M.J.; Alderweireldt, S.; Aleksa, M.; Aleksandrov, I.N.; Alexa, C.; Alexopoulos, T.; Alfonsi, A.; Alfonsi, F.; Alhroob, M.; Ali, B.; Ali, S.; Aliev, M.; Alimonti, G.; Allaire, C.; Allbrooke, B.M.M.; Allen, B.W.; Allport, P.P.; Aloisio, A.The performance of the ATLAS muon trigger system is evaluated with proton-proton (pp) and heavy-ion (HI) collision data collected in Run 2 during 2015–2018 at the Large Hadron Collider. It is primarily evaluated using events containing a pair of muons from the decay of Z bosons to cover the intermediate momentum range between 26 GeV and 100 GeV. Overall, the efficiency of the single-muon triggers is about 68% in the barrel region and 85% in the endcap region. The pT range for efficiency determination is extended by using muons from decays of J/ψ mesons, W bosons, and top quarks. The performance in HI collision data is measured and shows good agreement with the results obtained in pp collisions. The muon trigger shows uniform and stable performance in good agreement with the prediction of a detailed simulation. Dedicated multi-muon triggers with kinematic selections provide the backbone to beauty, quarkonia, and low-mass physics studies. The design, evolution and performance of these triggers are discussed in detail.Ítem Search for Dark Matter Produced in Association with a Dark Higgs Boson Decaying into W±Wa" or ZZ in Fully Hadronic Final States from s =13 TeV pp Collisions Recorded with the ATLAS Detector(American Physical Society, 2021-03) Aad, G.; Abbott, B.; Abbott, D.C.; Abed Abud, A.; Abeling, K.; Abhayasinghe, D.K.; Abidi, S.H.; Abouzeid, O.S.; Abraham, N.L.; Abramowicz, H. .; Abreu, H.; Abulaiti, Y.; Acharya, B.S.; Achkar, B.; Adam, L.; Adam Bourdarios, C.; Adamczyk, L.; Adamek, L.; Adelman, J.; Adiguzel, A.; Adorni, S.; Adye, T.; Affolder, A.A.Several extensions of the Standard Model predict the production of dark matter particles at the LHC. An uncharted signature of dark matter particles produced in association with VV=W±Wa"or ZZ pairs from a decay of a dark Higgs boson s is searched for using 139 fb-1 of pp collisions recorded by the ATLAS detector at a center-of-mass energy of 13 TeV. The s→V(qq)V(qq) decays are reconstructed with a novel technique aimed at resolving the dense topology from boosted VV pairs using jets in the calorimeter and tracking information. Dark Higgs scenarios with ms>160 GeV are excluded. © 2021 CERN.Ítem Search for long-lived neutral particles produced in pp collisions at ffisffi p =13 TeV decaying into displaced hadronic jets in the ATLAS inner detector and muon spectrometer(American Physical Society, 2020-03) Aad, G.; Abbott, B.; Abbott, D.C; Abed Abud, A; Abeling, K; Abhayasinghe, D.K; Abidi, S.H.; Abouzeid, O.S.; Abraham, N.L; Abramowicz, H.; Abreu, H; Abulaiti, Y.A search is presented for pair production of long-lived neutral particles using 33 fb-1 of s=13 TeV proton-proton collision data, collected during 2016 by the ATLAS detector at the LHC. This search focuses on a topology in which one long-lived particle decays in the ATLAS inner detector and the other decays in the muon spectrometer. Special techniques are employed to reconstruct the displaced tracks and vertices in the inner detector and in the muon spectrometer. One event is observed that passes the full event selection, which is consistent with the estimated background. Limits are placed on scalar boson propagators with masses from 125 GeV to 1000 GeV decaying into pairs of long-lived hidden-sector scalars with masses from 8 GeV to 400 GeV. The limits placed on several low-mass scalars extend previous exclusion limits in the range of proper lifetimes cτ from 5 cm to 1 m. © 2020 CERN.Ítem Search for new phenomena in pp collisions in final states with tau leptons, b -jets, and missing transverse momentum with the ATLAS detector(American Physical Society, 2021-12) Aad, G.; Abbott, B.; Abbott, D.C.; Abed, Abud A.; Abeling, K.; Abhayasinghe, D.K.; Abidi, S.H.; Abouzeid, O.S.; Abramowicz, H.; Abreu, H.; Abulaiti, Y.; Abusleme Hoffman, A.C.; Acharya, B.S.; Achkar, B.; Adam, L.; Adam Bourdarios, C.; Adamczyk, L.; Adamek, L.; Adelman, J.; Adiguzel, A.; Adorni, S.; Adye, T.; Affolder, A.A.; Afik, Y.; Agapopoulou, C.; Agaras, M.N.; Agarwala, J.; Aggarwal, A.; Agheorghiesei, C.; Aguilar-Saavedra, J.A.; Ahmad, A.; Ahmadov, F.; Ahmed, W.S.; Ai, X.; Aielli, G.; Akatsuka, S.; Akbiyik, M.; Åkesson, T.P.A.; Akimov, A.V.; Al Khoury, K.; Alberghi, G.L.; Albert, J.; Alconada Verzini, M.J.; Alderweireldt, S.; Aleksa, M.; Aleksandrov, I.N.; Alexa, C.; Alexopoulos, T.; Alfonsi, A.; Alfonsi, F.; Alhroob, M.; Ali, B.; Ali, S.; Aliev, M.; Alimonti, G.; Allaire, C.; Allbrooke, B.M.M.; Allport, P.P.; Aloisio, A.; Alonso, F.A search for new phenomena in final states with hadronically decaying tau leptons, b -jets, and missing transverse momentum is presented. The analyzed dataset comprises p p collision data at a center-of-mass energy of √ s = 13 TeV with an integrated luminosity of 139 fb − 1 , delivered by the Large Hadron Collider and recorded with the ATLAS detector from 2015 to 2018. The observed data are compatible with the expected Standard Model background. The results are interpreted in simplified models for two different scenarios. The first model is based on supersymmetry and considers pair production of top squarks, each of which decays into a b -quark, a neutrino and a tau slepton. Each tau slepton in turn decays into a tau lepton and a nearly massless gravitino. Within this model, top-squark masses up to 1.4 TeV can be excluded at the 95% confidence level over a wide range of tau-slepton masses. The second model considers pair production of leptoquarks with decays into third-generation leptons and quarks. Depending on the branching fraction into charged leptons, leptoquarks with masses up to around 1.25 TeV can be excluded at the 95% confidence level for the case of scalar leptoquarks and up to 1.8 TeV (1.5 TeV) for vector leptoquarks in a Yang–Mills (minimal-coupling) scenario. In addition, model-independent upper limits are set on the cross section of processes beyond the Standard Model.Ítem Searches for electroweak production of supersymmetric particles with compressed mass spectra in ffiffi s p =13 TeV pp collisions with the ATLAS detector(American Physical Society, 2020-03) Aad, G.; Abbott, B.; Abbott, D.C; Abed, Abud A; Abeling, K; Abhayasinghe, D.K; Abidi, S.H; Abouzeid, O.S.; Abraham, N.L; Abramowicz, H.; Abreu, H.; Abulaiti, Y.This paper presents results of searches for the electroweak production of supersymmetric particles in models with compressed mass spectra. The searches use 139 fb-1 of s=13 TeV proton-proton collision data collected by the ATLAS experiment at the Large Hadron Collider. Events with missing transverse momentum and two same-flavor, oppositely charged, low-transverse-momentum leptons are selected, and are further categorized by the presence of hadronic activity from initial-state radiation or a topology compatible with vector-boson fusion processes. The data are found to be consistent with predictions from the Standard Model. The results are interpreted using simplified models of R-parity-conserving supersymmetry in which the lightest supersymmetric partner is a neutralino with a mass similar to the lightest chargino, the second-to-lightest neutralino, or the slepton. Lower limits on the masses of charginos in different simplified models range from 193 to 240 GeV for moderate mass splittings, and extend down to mass splittings of 1.5 to 2.4 GeV at the LEP chargino bounds (92.4 GeV). Similar lower limits on degenerate light-flavor sleptons extend up to masses of 251 GeV and down to mass splittings of 550 MeV. Constraints on vector-boson fusion production of electroweak SUSY states are also presented. © 2020 CERN