| 1. |
- Aaboud, M, et al.
(författare)
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Measurement of jet pT correlations in Pb + Pb and pp collisions at sNN=2.76 TeVwith the ATLAS detector
- 2017
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 774, s. 379-402
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of dijet pT correlations in Pb+Pb and pp collisions at a nucleon–nucleon centre-of-mass energy of sNN=2.76 TeV are presented. The measurements are performed with the ATLAS detector at the Large Hadron Collider using Pb+Pb and pp data samples corresponding to integrated luminosities of 0.14 nb−1 and 4.0 pb−1, respectively. Jets are reconstructed using the anti-kt algorithm with radius parameter values R=0.3 and R=0.4. A background subtraction procedure is applied to correct the jets for the large underlying event present in Pb+Pb collisions. The leading and sub-leading jet transverse momenta are denoted pT1 and pT2. An unfolding procedure is applied to the two-dimensional (pT1,pT2) distributions to account for experimental effects in the measurement of both jets. Distributions of (1/N)dN/dxJ, where xJ=pT2/pT1, are presented as a function of pT1 and collision centrality. The distributions are found to be similar in peripheral Pb+Pb collisions and pp collisions, but highly modified in central Pb+Pb collisions. Similar features are present in both the R=0.3 and R=0.4 results, indicating that the effects of the underlying event are properly accounted for in the measurement. The results are qualitatively consistent with expectations from partonic energy loss models. © 2017 The Author
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| 2. |
- Abulaiti, Yiming, et al.
(författare)
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Femtoscopy with identified charged pions in proton-lead collisions at root s(NN)=5.02 TeV with ATLAS
- 2017
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Ingår i: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 96:6
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Tidskriftsartikel (refereegranskat)abstract
- Bose-Einstein correlations between identified charged pions are measured for p+Pb collisions at root s(NN) = 5.02 TeV using data recorded by the ATLAS detector at the CERN Large Hadron Collider corresponding to a total integrated luminosity of 28 nb(-1). Pions are identified using ionization energy loss measured in the pixel detector. Two-particle correlation functions and the extracted source radii are presented as a function of collision centrality as well as the average transverse momentum (k(T)) and rapidity (y*(pi pi)) of the pair. Pairs are selected with a rapidity -2 < y*(pi pi) < 1 and with an average transverse momentum 0.1 < k(T) < 0.8 GeV. The effect of jet fragmentation on the two-particle correlation function is studied, and a method using opposite-charge pair data to constrain its contributions to the measured correlations is described. The measured source sizes are substantially larger in more central collisions and are observed to decrease with increasing pair k(T). A correlation of the radii with the local charged-particle density is demonstrated. The scaling of the extracted radii with the mean number of participating nucleons is also used to compare a selection of initial-geometry models. The cross term R-ol is measured as a function of rapidity, and a nonzero value is observed with 5.1 sigma combined significance for -1 < y*pi pi < 1 in the most central events.
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| 3. |
- Abulaiti, Yiming, et al.
(författare)
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Jet reconstruction and performance using particle flow with the ATLAS Detector
- 2017
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052 .- 0143-0807 .- 1361-6404. ; 77:7
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes the implementation and performance of a particle flow algorithm applied to 20.2 fb(-1) of ATLAS data from 8 TeV proton-proton collisions in Run 1 of the LHC. The algorithm removes calorimeter energy deposits due to charged hadrons from consideration during jet reconstruction, instead using measurements of their momenta from the inner tracker. This improves the accuracy of the charged-hadron measurement, while retaining the calorimeter measurements of neutral-particle energies. The paper places emphasis on how this is achieved, while minimising double-counting of charged-hadron signals between the inner tracker and calorimeter. The performance of particle flow jets, formed from the ensemble of signals from the calorimeter and the inner tracker, is compared to that of jets reconstructed from calorimeter energy deposits alone, demonstrating improvements in resolution and pile-up stability.
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| 4. |
- Abulaiti, Yiming, et al.
(författare)
-
Measurement of charged-particle distributions sensitive to the underlying event in root s=13 TeV proton-proton collisions with the ATLAS detector at the LHC
- 2017
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Ingår i: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479. ; :3
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Tidskriftsartikel (refereegranskat)abstract
- We present charged-particle distributions sensitive to the underlying event, measured by the ATLAS detector in proton-proton collisions at a centre-of-mass energy of 13 TeV, in low-luminosity Large Hadron Collider fills corresponding to an integrated luminosity of 1.6 nb-1. The distributions were constructed using charged particles with absolute pseudorapidity less than 2.5 and with transverse momentum greater than 500 MeV, in events with at least one such charged particle with transverse momentum above 1 GeV. These distributions characterise the angular distribution of energy and particle flows with respect to the charged particle with highest transverse momentum, as a function of both that momentum and of charged-particle multiplicity. The results have been corrected for detector effects and are compared to the predictions of various Monte Carlo event generators, experimentally establishing the level of underlying-event activity at LHC Run 2 energies and providing inputs for the development of event generator modelling. The current models in use for UE modelling typically describe this data to 5% accuracy, compared with data uncertainties of less than 1%.
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| 5. |
- Abulaiti, Yiming, et al.
(författare)
-
Measurement of forward-backward multiplicity correlations in lead-lead, proton-lead, and proton-proton collisions with the ATLAS detector
- 2017
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Ingår i: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 95:6
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Tidskriftsartikel (refereegranskat)abstract
- Two-particle pseudorapidity correlations are measured in root s(NN) = 2.76 TeV Pb + Pb, root s(NN) = 5.02 TeV p+Pb, and root s = 13 TeV pp collisions at the Large Hadron Collider (LHC), with total integrated luminosities of approximately 7 mu b(-1), 28 nb(-1), and 65 nb(-1), respectively. The correlation function CN(eta(1),eta(2))is measured as a function of event multiplicity using charged particles in the pseudorapidity range |eta| < 2.4. The correlation function contains a significant short-range component, which is estimated and subtracted. After removal of the short-range component, the shape of the correlation function is described approximately by 1 + < a(1)(2)>(1/2) eta(1) eta(2) in all collision systems over the full multiplicity range. The values of < a(1)(2)>(1/2) are consistent for the opposite-charge pairs and same-charge pairs, and for the three collision systems at similar multiplicity. The values of < a(1)(2)>(1/2) and the magnitude of the short-range component both follow a power-law dependence on the event multiplicity. The short-range component in p + Pb collisions, after symmetrizing the proton and lead directions, is found to be smaller at a given eta than in pp collisions with comparable multiplicity.
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| 6. |
- Abulaiti, Yiming, et al.
(författare)
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Measurement of jet activity produced in top-quark events with an electron, a muon and two b-tagged jets in the final state in pp collisions root s=13TeV with the ATLAS detector
- 2017
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 77:4
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of jet activity in top-quark pair events produced in proton-proton collisions are presented, using 3.2 fb of pp collision data at a centre-of-mass energy of 13 TeV collected by the ATLAS experiment at the Large Hadron Collider. Events are chosen by requiring an opposite-charge pair and two b-tagged jets in the final state. The normalised differential cross-sections of top-quark pair production are presented as functions of additional-jet multiplicity and transverse momentum, . The fraction of signal events that do not contain additional jet activity in a given rapidity region, the gap fraction, is measured as a function of the threshold for additional jets, and is also presented for different invariant mass regions of the system. All measurements are corrected for detector effects and presented as particle-level distributions compared to predictions with different theoretical approaches for QCD radiation. While the kinematics of the jets from top-quark decays are described well, the generators show differing levels of agreement with the measurements of observables that depend on the production of additional jets.
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| 7. |
- Abulaiti, Yiming, et al.
(författare)
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Measurement of the cross section for inclusive isolated-photon production in pp collisions at root s=13 TeV using the ATLAS detector
- 2017
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 770, s. 473-493
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Tidskriftsartikel (refereegranskat)abstract
- Inclusive isolated-photon production in pp collisions at a centre-of-mass energy of 13 TeV is studied with the ATLAS detector at the LHC using a data set with an integrated luminosity of 3.2 fb(-1). The cross section is measured as a function of the photon transverse energy above 125 GeV in different regions of photon pseudorapidity. Next-to-leading-order perturbative QCD and Monte Carlo event-generator predictions are compared to the cross-section measurements and provide an adequate description of the data.
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| 8. |
- Abulaiti, Yiming, et al.
(författare)
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Measurement of the W+ W- production cross section in pp collisions at a centre-of-mass energy of root s=13 TeV with the ATLAS experiment
- 2017
-
Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 773, s. 354-374
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Tidskriftsartikel (refereegranskat)abstract
- The production of opposite-charge W-boson pairs in proton-proton collisions at root s = 13 TeV is measured using data corresponding to 3.16 fb(-1) of integrated luminosity collected by the ATLAS detector at the CERN Large Hadron Collider in 2015. Candidate W-boson pairs are selected by identifying their leptonic decays into an electron, a muon and neutrinos. Events with reconstructed jets are not included in the candidate event sample. The cross-section measurement is performed in a fiducial phase space close to the experimental acceptance and is compared to theoretical predictions. Agreement is found between the measurement and the most accurate calculations available.
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| 9. |
- Abulaiti, Yiming, et al.
(författare)
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Measurements of psi(2S) and X(3872) -> J/psi pi (+) pi (-) production in pp collisions at root s=8 Tev with the ATLAS detector
- 2017
-
Ingår i: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479. ; :1:1
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Tidskriftsartikel (refereegranskat)abstract
- Differential cross sections are presented for the prompt and non-prompt production of the hidden-charm states X(3872) and psi(2S), in the decay mode J/psi pi (+) pi (-), measured using 11.4 fb(-1) of pp collisions at root s = 8 Tev by the ATLAS detector at the LHC. The ratio of cross-sections X(3872)/psi(2S) is also given, separately for prompt and non-prompt components, as well as the non-prompt fractions of X(3872) and psi(2S). Assuming independent single effective lifetimes for non-prompt X(3872) and psi(2S) production gives separating short- and long-lived contributions, assuming that the short-lived component is due to B (c) decays, gives R (B) = (3.57 +/- 0.33(stat) +/- 0.11(sys)) x 10(-2), with the fraction of non-prompt X(3872) produced via B (c) decays for p (T)(X(3872)) > 10 GeV being (25 +/- 13(stat) +/- 2(sys) +/- 5(spin))%. The distributions of the dipion invariant mass in the X(3872) and psi(2S) decays are also measured and compared to theoretical predictions.
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| 10. |
- Abulaiti, Yiming, et al.
(författare)
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Precision measurement and interpretation of inclusive W+, W- and Z/gamma* production cross sections with the ATLAS detector
- 2017
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 77:6
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Tidskriftsartikel (refereegranskat)abstract
- High-precision measurements by the ATLAS Collaboration are presented of inclusive W+ -> l(+) nu, W- -> l(-) (nu) over bar and Z/gamma* -> ll (l = e, mu) Drell-Yan production cross sections at the LHC. The data were collected in proton-proton collisions at root s = 7 TeV with an integrated luminosity of 4.6 fb(-1). Differential W+ and W- cross sections are measured in a lepton pseudorapidity range vertical bar eta(l)vertical bar < 2.5. Differential Z/gamma* cross sections are measured as a function of the absolute dilepton rapidity, for vertical bar y(ll)vertical bar < 3.6, for three intervals of dilepton mass, m(ll), extending from 46 to 150 GeV. The integrated and differential electron- and muon-channel cross sections are combined and compared to theoretical predictions using recent sets of parton distribution functions. The data, together with the final inclusive e(+/-) p scattering cross-section data from H1 and ZEUS, are interpreted in a next-to-next-to-leading-order QCD analysis, and a new set of parton distribution functions, ATLAS-epWZ16, is obtained. The ratio of strange-to-light sea-quark densities in the proton is determined more accurately than in previous determinations based on collider data only, and is established to be close to unity in the sensitivity range of the data. A new measurement of the CKM matrix element vertical bar V-cs vertical bar is also provided.
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