| 31. |
- M., Aaboud, et al.
(författare)
-
Dijet azimuthal correlations and conditional yields in pp and p+Pb collisions at sNN=5.02TeV with the ATLAS detector
- 2019
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Ingår i: Physical Review C. - 2469-9985 .- 2469-9993. ; 100:3
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a measurement of forward-forward and forward-central dijet azimuthal angular correlations and conditional yields in proton-proton (pp) and proton-lead (p+Pb) collisions as a probe of the nuclear gluon density in regions where the fraction of the average momentum per nucleon carried by the parton entering the hard scattering is low. In these regions, gluon saturation can modify the rapidly increasing parton distribution function of the gluon. The analysis utilizes 25pb-1 of pp data and 360μb-1 of p+Pb data, both at sNN=5.02 TeV, collected in 2015 and 2016, respectively, with the ATLAS detector at the Large Hadron Collider. The measurement is performed in the center-of-mass frame of the nucleon-nucleon system in the rapidity range between -4.0 and 4.0 using the two highest transverse-momentum jets in each event, with the highest transverse-momentum jet restricted to the forward rapidity range. No significant broadening of azimuthal angular correlations is observed for forward-forward or forward-central dijets in p+Pb compared to pp collisions. For forward-forward jet pairs in the proton-going direction, the ratio of conditional yields in p+Pb collisions to those in pp collisions is suppressed by approximately 20%, with no significant dependence on the transverse momentum of the dijet system. No modification of conditional yields is observed for forward-central dijets. © 2019 CERN.
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| 32. |
- M., Aaboud, et al.
(författare)
-
Measurement of the tt¯Z and tt¯W cross sections in proton-proton collisions at s=13 TeV with the ATLAS detector
- 2019
-
Ingår i: Physical Review D. - 2470-0010. ; 99:7
-
Tidskriftsartikel (refereegranskat)abstract
- A measurement of the associated production of a top-quark pair (tt) with a vector boson (W, Z) in proton-proton collisions at a center-of-mass energy of 13 TeV is presented, using 36.1 fb-1 of integrated luminosity collected by the ATLAS detector at the Large Hadron Collider. Events are selected in channels with two same- or opposite-sign leptons (electrons or muons), three leptons or four leptons, and each channel is further divided into multiple regions to maximize the sensitivity of the measurement. The ttZ and ttW production cross sections are simultaneously measured using a combined fit to all regions. The best-fit values of the production cross sections are σttZ=0.95±0.08stat±0.10syst pb and σttW=0.87±0.13stat±0.14syst pb in agreement with the Standard Model predictions. The measurement of the ttZ cross section is used to set constraints on effective field theory operators which modify the ttZ vertex. © 2019 CERN, for the ATLAS Collaboration.
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| 33. |
- M., Aaboud, et al.
(författare)
-
Search for heavy charged long-lived particles in the ATLAS detector in 36.1 fb-1 of proton-proton collision data at s =13 TeV
- 2019
-
Ingår i: Physical Review D. - 2470-0010. ; 99:9
-
Tidskriftsartikel (refereegranskat)abstract
- A search for heavy charged long-lived particles is performed using a data sample of 36.1 fb-1 of proton-proton collisions at s=13 TeV collected by the ATLAS experiment at the Large Hadron Collider. The search is based on observables related to ionization energy loss and time of flight, which are sensitive to the velocity of heavy charged particles traveling significantly slower than the speed of light. Multiple search strategies for a wide range of lifetimes, corresponding to path lengths of a few meters, are defined as model independently as possible, by referencing several representative physics cases that yield long-lived particles within supersymmetric models, such as gluinos/squarks (R-hadrons), charginos and staus. No significant deviations from the expected Standard Model background are observed. Upper limits at 95% confidence level are provided on the production cross sections of long-lived R-hadrons as well as directly pair-produced staus and charginos. These results translate into lower limits on the masses of long-lived gluino, sbottom and stop R-hadrons, as well as staus and charginos of 2000, 1250, 1340, 430, and 1090 GeV, respectively. © 2019 CERN. for the ATLAS Collaboration. 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.
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| 34. |
- Milstead, David A., et al.
(författare)
-
Combination of Searches for Invisible Higgs Boson Decays with the ATLAS Experiment
- 2019
-
Ingår i: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 122:23
-
Tidskriftsartikel (refereegranskat)abstract
- Dark matter particles, if sufficiently light, may be produced in decays of the Higgs boson. This Letter presents a statistical combination of searches for H→invisible decays where H is produced according to the standard model via vector boson fusion, Z(-)H, and W/Z(had)H, all performed with the ATLAS detector using 36.1 fb-1 of pp collisions at a center-of-mass energy of s=13 TeV at the LHC. In combination with the results at s=7 and 8 TeV, an exclusion limit on the H→invisible branching ratio of 0.26(0.17-0.05+0.07) at 95% confidence level is observed (expected). © 2019 CERN.
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| 35. |
- Milstead, David A., et al.
(författare)
-
Electron reconstruction and identification in the ATLAS experiment using the 2015 and 2016 LHC proton–proton collision data at √s=13 TeV
- 2019
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 79:8
-
Tidskriftsartikel (refereegranskat)abstract
- Algorithms used for the reconstruction and identification of electrons in the central region of the ATLAS detector at the Large Hadron Collider (LHC) are presented in this paper; these algorithms are used in ATLAS physics analyses that involve electrons in the final state and which are based on the 2015 and 2016 proton–proton collision data produced by the LHC at s = 13 TeV. The performance of the electron reconstruction, identification, isolation, and charge identification algorithms is evaluated in data and in simulated samples using electrons from Z→ ee and J/ ψ→ ee decays. Typical examples of combinations of electron reconstruction, identification, and isolation operating points used in ATLAS physics analyses are shown. © 2019, CERN for the benefit of the ATLAS collaboration.
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| 36. |
- Milstead, David A., et al.
(författare)
-
Search for heavy particles decaying into a top-quark pair in the fully hadronic final state in pp collisions at s =13 TeV with the ATLAS detector
- 2019
-
Ingår i: Physical Review D. - : American Physical Society. - 2470-0010 .- 2470-0029. ; 99:9
-
Tidskriftsartikel (refereegranskat)abstract
- A search for new particles decaying into a pair of top quarks is performed using proton-proton collision data recorded with the ATLAS detector at the Large Hadron Collider at a center-of-mass energy of s=13 TeV corresponding to an integrated luminosity of 36.1 fb-1. Events consistent with top-quark pair production and the fully hadronic decay mode of the top quarks are selected by requiring multiple high transverse momentum jets including those containing b-hadrons. Two analysis techniques, exploiting dedicated top-quark pair reconstruction in different kinematic regimes, are used to optimize the search sensitivity to new hypothetical particles over a wide mass range. The invariant mass distribution of the two reconstructed top-quark candidates is examined for resonant production of new particles with various spins and decay widths. No significant deviation from the Standard Model prediction is observed and limits are set on the production cross-section times branching fraction for new hypothetical Z′ bosons, dark-matter mediators, Kaluza-Klein gravitons and Kaluza-Klein gluons. By comparing with the predicted production cross sections, the Z′ boson in the topcolor-assisted-technicolor model is excluded for masses up to 3.1-3.6 TeV, the dark-matter mediators in a simplified framework are excluded in the mass ranges from 0.8 to 0.9 TeV and from 2.0 to 2.2 TeV, and the Kaluza-Klein gluon is excluded for masses up to 3.4 TeV, depending on the decay widths of the particles. © 2019 CERN, for the ATLAS Collaboration.
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| 37. |
- Aaboud, M, et al.
(författare)
-
ATLAS Collaboration
- 2017
-
Ingår i: Nuclear Physics A. - : Elsevier. - 0375-9474 .- 1873-1554. ; 967, s. 942-964
-
Tidskriftsartikel (refereegranskat)
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| 38. |
- Aaboud, M, et al.
(författare)
-
Charged-particle distributions at low transverse momentum in √s=13 TeV pp interactions measured with the ATLAS detector at the LHC
- 2016
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 76:9
-
Tidskriftsartikel (refereegranskat)abstract
- Measurements of distributions of charged particles produced in proton–proton collisions with a centre-of-mass energy of 13 TeV are presented. The data were recorded by the ATLAS detector at the LHC and correspond to an integrated luminosity of 151 μ b - 1. The particles are required to have a transverse momentum greater than 100 MeV and an absolute pseudorapidity less than 2.5. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity and the dependence of the mean transverse momentum on multiplicity are measured in events containing at least two charged particles satisfying the above kinematic criteria. The results are corrected for detector effects and compared to the predictions from several Monte Carlo event generators. © 2016, CERN for the benefit of the ATLAS collaboration.
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| 39. |
- Aaboud, M, et al.
(författare)
-
Combination of inclusive and differential (Formula Presented) charge asymmetry measurements using ATLAS and CMS data at (Formula Presented)= 7 and 8 TeV
- 2018
-
Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2018:4
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents combinations of inclusive and differential measurements of the charge asymmetry (AC) in top quark pair (tt) events with a lepton+jets signature by the ATLAS and CMS Collaborations, using data from LHC proton-proton collisions at centreof- mass energies of 7 and 8TeV. The data correspond to integrated luminosities of about 5 and 20 fb–1for each experiment, respectively. The resulting combined LHC measurements of the inclusive charge asymmetry are AC LHC7= 0:005±0:007 (stat) ±0:006 (syst) at 7TeV and AC LHC7= 0:0055 ± 0:0023 (stat) ± 0:0025 (syst) at 8TeV. These values, as well as the combination of AC measurements as a function of the invariant mass of the [formula presented] system at 8TeV, are consistent with the respective standard model predictions. © CERN, for the benefit of the ATLAS-CMS Collaboration.
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| 40. |
- Aaboud, M, et al.
(författare)
-
Determination of the strong coupling constant αs from transverse energy–energy correlations in multijet events at √s=8TeV using the ATLAS detector
- 2017
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 77:12
-
Tidskriftsartikel (refereegranskat)abstract
- Measurements of transverse energy–energy correlations and their associated asymmetries in multi-jet events using the ATLAS detector at the LHC are presented. The data used correspond to s=8TeV proton–proton collisions with an integrated luminosity of 20.2fb-1. The results are presented in bins of the scalar sum of the transverse momenta of the two leading jets, unfolded to the particle level and compared to the predictions from Monte Carlo simulations. A comparison with next-to-leading-order perturbative QCD is also performed, showing excellent agreement within the uncertainties. From this comparison, the value of the strong coupling constant is extracted for different energy regimes, thus testing the running of αs(μ) predicted in QCD up to scales over 1TeV. A global fit to the transverse energy–energy correlation distributions yields αs(mZ)=0.1162±0.0011(exp.)-0.0070+0.0084(theo.), while a global fit to the asymmetry distributions yields a value of αs(mZ)=0.1196±0.0013(exp.)-0.0045+0.0075(theo.). © 2017, CERN for the benefit of the ATLAS collaboration.
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