Examinando por Autor "Hoffman, A. C. Abusleme"
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Ítem Calibration of the light-flavour jet mistagging efficiency of the b-tagging algorithms with Z+jets events using 139 fb - 1 of ATLAS proton–proton collision data at √s=13 TeV(Institute for Ionics, 2023-08) Aad G.; Abbott, B.; Abbott, D.C; Abeling, K.; Abidi, S.H.; Aboulhorma, A.; Abramowicz, H.; Abreu, H.; Abulaiti, Y.; Hoffman, A. C. Abusleme; Acharya, B.S.; Bourdarios, C. AdamThe identification of b-jets, referred to as b-tagging, is an important part of many physics analyses in the ATLAS experiment at the Large Hadron Collider and an accurate calibration of its performance is essential for high-quality physics results. This publication describes the calibration of the light-flavour jet mistagging efficiency in a data sample of proton–proton collision events at s=13 TeV corresponding to an integrated luminosity of 139 fb - 1 . The calibration is performed in a sample of Z bosons produced in association with jets. Due to the low mistagging efficiency for light-flavour jets, a method which uses modified versions of the b-tagging algorithms referred to as flip taggers is used in this work. A fit to the jet-flavour-sensitive secondary-vertex mass is performed to extract a scale factor from data, to correct the light-flavour jet mistagging efficiency in Monte Carlo simulations, while simultaneously correcting the b-jet efficiency. With this procedure, uncertainties coming from the modeling of jets from heavy-flavour hadrons are considerably lower than in previous calibrations of the mistagging scale factors, where they were dominant. The scale factors obtained in this calibration are consistent with unity within uncertainties.Ítem Determination of the parton distribution functions of the proton using diverse ATLAS data from pp collisions at √s=7 , 8 and 13 TeV(Institute for Ionics, 2022-05) Aad, G.; Abbott, B.; Abbott, D.C.; Abud, A. Abed; Abeling, K.; Abhayasinghe, D.K.; Abidi, S.H.; Aboulhorma, A.; Abramowicz, H.; Abreu, H.; Abulaiti, Y.; Hoffman, A. C. Abusleme; Acharya, B.S.; Achkar, B.; Adam, L.; Bourdarios, C. Adam; Adamczyk, L.; Adamek, L.; Addepalli, S.V.; 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.; Aizenberg, I.; Akbiyik, M.; Åkesson, T.P.A.; Akimov, A.V.; Khoury, K. Al; Alberghi, G.L.; Albert, J.; Albicocco, P.; Verzini, M. J. Alconada; 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.This paper presents an analysis at next-to-next-to-leading order in the theory of quantum chromodynamics for the determination of a new set of proton parton distribution functions using diverse measurements in pp collisions at s=7, 8 and 13 TeV, performed by the ATLAS experiment at the Large Hadron Collider, together with deep inelastic scattering data from ep collisions at the HERA collider. The ATLAS data sets considered are differential cross-section measurements of inclusive W± and Z/ γ∗ boson production, W± and Z boson production in association with jets, tt¯ production, inclusive jet production and direct photon production. In the analysis, particular attention is paid to the correlation of systematic uncertainties within and between the various ATLAS data sets and to the impact of model, theoretical and parameterisation uncertainties. The resulting set of parton distribution functions is called ATLASpdf21. © 2022, The Author(s).Ítem Direct constraint on the Higgs–charm coupling from a search for Higgs boson decays into charm quarks with the ATLAS detector(Institute for Ionics, 2022-08) Aad, G.; Abbott, B.; Abbott, D.C.; Abud, A. Abed; Abeling, K.; Abhayasinghe, D.K.; Abidi, S.H.; Aboulhorma, A.; Abramowicz, H.; Abreu, H.; Abulaiti, Y.; Hoffman, A. C. Abusleme; Acharya, B.S.; Achkar, B.; Adam, L.; Bourdarios, C. Adam; Adamczyk, L.; Adamek, L.; Addepalli, S.V.; Adelman, J.; Adiguzel, A.; Adorni, S.; Adye, T.; Affolder, A.A.; Afik, Y.; Agaras, M.N.; Agarwala, J.; Aggarwal, A.; Agheorghiesei, C.; Aguilar Saavedra, J.A.; Ahmad, A.; Ahmadov, F.; Ahmed, W.S.; Ai, X.; Aielli, G.; Aizenberg, I.; Akbiyik, M.; Åkesson, T.P.A.; Akimov, A.V.; Khoury, K. Al; Alberghi, G.L.; Albert, J.; Albicocco, P.; Verzini, M. J. Alconada; 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.A search for the Higgs boson decaying into a pair of charm quarks is presented. The analysis uses proton–proton collisions to target the production of a Higgs boson in association with a leptonically decaying W or Z boson. The dataset delivered by the LHC at a centre-of-mass energy of [InlineEquation not available: see fulltext.] and recorded by the ATLAS detector corresponds to an integrated luminosity of 139 fb-1. Flavour-tagging algorithms are used to identify jets originating from the hadronisation of charm quarks. The analysis method is validated with the simultaneous measurement of WW, WZ and ZZ production, with observed (expected) significances of 2.6 (2.2) standard deviations above the background-only prediction for the (W/ Z) Z(→ cc¯) process and 3.8 (4.6) standard deviations for the (W/ Z) W(→ cq) process. The (W/ Z) H(→ cc¯) search yields an observed (expected) upper limit of 26 (31) times the predicted Standard Model cross-section times branching fraction for a Higgs boson with a mass of [InlineEquation not available: see fulltext.], corresponding to an observed (expected) constraint on the charm Yukawa coupling modifier |κc|<8.5(12.4), at the 95% confidence level. A combination with the ATLAS (W/ Z) H, H→ bb¯ analysis is performed, allowing the ratio κc/ κb to be constrained to less than 4.5 at the 95% confidence level, smaller than the ratio of the b- and c-quark masses, and therefore determines the Higgs-charm coupling to be weaker than the Higgs-bottom coupling at the 95% confidence level. © 2022, The Author(s).Ítem Measurement of the energy asymmetry in tt¯ j production at 13 TeV with the ATLAS experiment and interpretation in the SMEFT framework(Institute for Ionics, 2022-04) Aad, G.; Abbott, B.; Abbott, D.C.; Abud, A. Abed; Abeling, K.; Abhayasinghe, D.K.; Abidi, S.H.; Aboulhorma, A.; Abramowicz, H.; Abreu, H.; Abulaiti, Y.; Hoffman, A. C. Abusleme; Acharya, B.S.; Achkar, B.; Adam, L.; Bourdarios, C. Adam; Adamczyk, L.; Adamek, L.; Addepalli, S.V.; 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.; Aizenberg, I.; Akatsuka, S.; Akbiyik, M.; Åkesson, T.P.A.; Akimov, A.V.; Khoury, K. Al; Alberghi, G.L.; Albert, J.; Albicocco, P.; Verzini, M. J. Alconada; 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.A measurement of the energy asymmetry in jet-associated top-quark pair production is presented using 139fb-1 of data collected by the ATLAS detector at the Large Hadron Collider during pp collisions at s=13TeV. The observable measures the different probability of top and antitop quarks to have the higher energy as a function of the jet scattering angle with respect to the beam axis. The energy asymmetry is measured in the semileptonic tt¯ decay channel, and the hadronically decaying top quark must have transverse momentum above 350GeV. The results are corrected for detector effects to particle level in three bins of the scattering angle of the associated jet. The measurement agrees with the SM prediction at next-to-leading-order accuracy in quantum chromodynamics in all three bins. In the bin with the largest expected asymmetry, where the jet is emitted perpendicular to the beam, the energy asymmetry is measured to be - 0.043 ± 0.020 , in agreement with the SM prediction of - 0.037 ± 0.003. Interpreting this result in the framework of the Standard Model effective field theory (SMEFT), it is shown that the energy asymmetry is sensitive to the top-quark chirality in four-quark operators and is therefore a valuable new observable in global SMEFT fits. © 2022, The Author(s).Ítem Measurement of the energy response of the ATLAS calorimeter to charged pions from W±→ τ±(→ π±ντ) ντ events in Run 2 data(Institute for Ionics, 2022-03) Aad, G.; Abbott, B.; Abbott, D.C.; Abud, A. Abed; Abeling, K.; Abhayasinghe, D.K.; Abidi, S.H.; Aboulhorma, A.; Abramowicz, H.; Abreu, H.; Abulaiti, Y.; Hoffman, A. C. Abusleme; Acharya, B.S.; Achkar, B.; Adam, L.; Bourdarios, C. Adam; Adamczyk, L.; Adamek, L.; Addepalli, S.V.; 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.; Aizenberg, I.; Akatsuka, S.; Akbiyik, M.; Åkesson, T.P.A.; Akimov, A.V.; Khoury, K. Al; Alberghi, G.L.; Albert, J.; Albicocco, P.; Verzini, M. J. Alconada; 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.The energy response of the ATLAS calorimeter is measured for single charged pions with transverse momentum in the range 10 < pT< 300 GeV. The measurement is performed using 139 fb - 1 of LHC proton–proton collision data at s=13 TeV taken in Run 2 by the ATLAS detector. Charged pions originating from τ-lepton decays are used to provide a sample of high-pT isolated particles, where the composition is known, to test an energy regime that has not previously been probed by in situ single-particle measurements. The calorimeter response to single-pions is observed to be overestimated by ∼ 2 % across a large part of the pT spectrum in the central region and underestimated by ∼ 4 % in the endcaps in the ATLAS simulation. The uncertainties in the measurements are ≲ 1 % for 15 < pT< 185 GeV in the central region. To investigate the source of the discrepancies, the width of the distribution of the ratio of calorimeter energy to track momentum, the energies per layer and response in the hadronic calorimeter are also compared between data and simulation. © 2022, The Author(s).Ítem Measurement of the nuclear modification factor of b-jets in 5.02 TeV Pb+Pb collisions with the ATLAS detector(Institute for Ionics, 2023-05) Aad, G.; Abbott, B.; Abbott, D.C.; Abeling, K.; Abidi, S.H.; Aboulhorma, A.; Abramowicz, H.; Abreu, H.; Abulaiti, Y.; Hoffman, A. C. Abusleme; Acharya, B.S.; Achkar, B.This paper presents a measurement of b-jet production in Pb+Pb and pp collisions at sNN=5.02 TeV with the ATLAS detector at the LHC. The measurement uses 260 pb - 1 of pp collisions collected in 2017 and 1.4 nb - 1 of Pb+Pb collisions collected in 2018. In both collision systems, jets are reconstructed via the anti- kt algorithm. The b-jets are identified from a sample of jets containing muons from the semileptonic decay of b-quarks using template fits of the muon momentum relative to the jet axis. In pp collisions, b-jets are reconstructed for radius parameters R= 0.2 and R= 0.4 , and only R= 0.2 jets are used in Pb+Pb collisions. For comparison, inclusive R= 0.2 jets are also measured using 1.7 nb - 1 of Pb+Pb collisions collected in 2018 and the same pp collision data as the b-jet measurement. The nuclear modification factor, RAA , is calculated for both b-jets and inclusive jets with R= 0.2 over the transverse momentum range of 80–290 GeV. The nuclear modification factor for b-jets decreases from peripheral to central collisions. The ratio of the b-jet RAA to inclusive jet RAA is also presented and suggests that the RAA for b-jets is larger than that for inclusive jets in central Pb+Pb collisions. The measurements are compared with theoretical calculations and suggest a role for mass and colour-charge effects in partonic energy loss in heavy-ion collisions.Ítem Observation of electroweak production of two jets in association with an isolated photon and missing transverse momentum, and search for a Higgs boson decaying into invisible particles at 13 TeV with the ATLAS detector(Institute for Ionics, 2022-02) Aad, G.; Abbott, B.; Abbott, D.C.; Abud, A. Abed; Abeling, K.; Abhayasinghe, D.K.; Abidi, S.H.; Aboulhorma, A.; Abramowicz, H.; Abreu, H.; Abulaiti, Y.; Hoffman, A. C. Abusleme; Acharya, B.S.; Achkar, B.; Adam, L.; Bourdarios, C. Adam; Adamczyk, L.; Adamek, L.; Addepalli, S.V.; 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.; Aizenberg, I.; Akatsuka, S.; Akbiyik, M.; Åkesson, T.P.A.; Akimov, A.V.; Khoury, K. Al; Alberghi, G.L.; Albert, J.; Albicocco, P.; Verzini, M. J. Alconada; 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.This paper presents a measurement of the electroweak production of two jets in association with a Zγ pair, with the Z boson decaying into two neutrinos. It also presents a search for invisible or partially invisible decays of a Higgs boson with a mass of 125 GeV produced through vector-boson fusion with a photon in the final state. These results use data from LHC proton–proton collisions at s = 13 TeV collected with the ATLAS detector and corresponding to an integrated luminosity of 139 fb - 1. The event signature, shared by all benchmark processes considered for the measurements and searches, is characterized by a significant amount of unbalanced transverse momentum and a photon in the final state, in addition to a pair of forward jets. Electroweak Zγ production in association with two jets is observed in this final state with a significance of 5.2 (5.1 expected) standard deviations. The measured fiducial cross-section for this process is 1.31 ± 0.29 fb. An observed (expected) upper limit of 0.37 (0.34-0.10+0.15) at 95% confidence level is set on the branching ratio of a 125 GeV Higgs boson to invisible particles, assuming the Standard Model production cross-section. The signature is also interpreted in the context of decays of a Higgs boson into a photon and a dark photon. An observed (expected) 95% CL upper limit on the branching ratio for this decay is set at 0.018 (0.017-0.005+0.007), assuming the Standard Model production cross-section for a 125 GeV Higgs boson. © 2022, The Author(s).Ítem Observation of four-top-quark production in the multilepton final state with the ATLAS detector(Institute for Ionics, 2023-07) Aad, G.; Abbott, B.; Abeling, K.; Abicht, N.J.; Abidi, S.H.; Aboulhorma, A.; Abramowicz, H.; Abreu, H.; Abulaiti, Y.; Hoffman, A. C. Abusleme; Acharya, B.S.; Bourdarios, C. AdamThis paper presents the observation of four-top-quark (tt¯ tt¯) production in proton-proton collisions at the LHC. The analysis is performed using an integrated luminosity of 140 fb - 1 at a centre-of-mass energy of 13 TeV collected using the ATLAS detector. Events containing two leptons with the same electric charge or at least three leptons (electrons or muons) are selected. Event kinematics are used to separate signal from background through a multivariate discriminant, and dedicated control regions are used to constrain the dominant backgrounds. The observed (expected) significance of the measured tt¯ tt¯ signal with respect to the standard model (SM) background-only hypothesis is 6.1 (4.3) standard deviations. The tt¯ tt¯ production cross section is measured to be 22.5-5.5+6.6 fb, consistent with the SM prediction of 12.0 ± 2.4 fb within 1.8 standard deviations. Data are also used to set limits on the three-top-quark production cross section, being an irreducible background not measured previously, and to constrain the top-Higgs Yukawa coupling and effective field theory operator coefficients that affect tt¯ tt¯ production.