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Johansson, K. Erik
Alternative names
Publications (10 of 315) Show all publications
Abulaiti, Y., Åkerstedt, H., Åsman, B., Bendtz, K., Bertoli, G., Bessidskaia Bylund, O., . . . Tylmad, M. (2016). Centrality, rapidity, and transverse momentum dependence of isolated prompt photon production in lead-lead collisions at root S-NN=2.76 TeV measured with the ATLAS detector. Physical Review C, 93(3), Article ID 034914.
Open this publication in new window or tab >>Centrality, rapidity, and transverse momentum dependence of isolated prompt photon production in lead-lead collisions at root S-NN=2.76 TeV measured with the ATLAS detector
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2016 (English)In: Physical Review C, ISSN 2469-9985, Vol. 93, no 3, article id 034914Article in journal (Refereed) Published
Abstract [en]

Prompt photon production in root S-NN = 2.76-TeV Pb + Pb collisions has been measured by the ATLAS experiment at the Large Hadron Collider using data collected in 2011 with an integrated luminosity of 0.14 nb(-1). Inclusive photon yields, scaled by the mean nuclear thickness function, are presented as a function of collision centrality and transverse momentum in two pseudorapidity intervals, vertical bar eta vertical bar < 1.37 and 1.52 <= vertical bar eta vertical bar < 2.37. The scaled yields in the two pseudorapidity intervals, as well as the ratios of the forward yields to those at midrapidity, are compared to the expectations from next-to-leading-order perturbative QCD (pQCD) calculations. The measured cross sections agree well with the predictions for proton-proton collisions within statistical and systematic uncertainties. Both the yields and the ratios are also compared to two other pQCD calculations, one which uses the isospin content appropriate to colliding lead nuclei and another which includes nuclear modifications to the nucleon parton distribution functions.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-130143 (URN)10.1103/PhysRevC.93.034914 (DOI)000372800000003 ()
Available from: 2016-05-17 Created: 2016-05-09 Last updated: 2022-03-23Bibliographically approved
Abulaiti, Y., Åsman, B., Bendtz, K., Bessidskaia Bylund, O., Bohm, C., Clément, C., . . . Tylmad, M. (2016). Measurement of the centrality dependence of the charged-particle pseudorapidity distribution in proton-lead collisions at root s(NN)=5.02 TeV with the ATLAS detector. European Physical Journal C, 76(4), Article ID 199.
Open this publication in new window or tab >>Measurement of the centrality dependence of the charged-particle pseudorapidity distribution in proton-lead collisions at root s(NN)=5.02 TeV with the ATLAS detector
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2016 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 76, no 4, article id 199Article in journal (Refereed) Published
Abstract [en]

The centrality dependence of the mean charged-particle multiplicity as a function of pseudorapidity is measured in approximately 1 mu b(-1) of proton-lead collisions at a nucleon-nucleon centre-of-mass energy of root s(NN) = 5.02 TeV using the ATLAS detector at the Large Hadron Collider. Charged particles with absolute pseudorapidity less than 2.7 are reconstructed using the ATLAS pixel detector. The p + Pb collision centrality is characterised by the total transverse energy measured in the Pb-going direction of the forward calorimeter. The charged-particle pseudorapidity distributions are found to vary strongly with centrality, with an increasing asymmetry between the proton-going and Pb-going directions as the collisions become more central. Three different estimations of the number of nucleons participating in the p + Pb collision have been carried out using the Glauber model as well as two Glauber-Gribov inspired extensions to the Glauber model. Charged-particle multiplicities per participant pair are found to vary differently for these three models, highlighting the importance of including colour fluctuations in nucleon-nucleon collisions in the modelling of the initial state of p + Pb collisions.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-130878 (URN)10.1140/epjc/s10052-016-4002-3 (DOI)000375306400002 ()
Available from: 2016-06-07 Created: 2016-06-07 Last updated: 2022-03-23Bibliographically approved
Abdallah, J., Alexa, C., Amaral Coutinho, Y., Amor Dos Santos, S. P., Anderson, K. J., Arabidze, G., . . . van Woerden, M. C. (2016). The Laser calibration of the ATLAS Tile Calorimeter during the LHC run 1. Journal of Instrumentation, 11, Article ID T10005.
Open this publication in new window or tab >>The Laser calibration of the ATLAS Tile Calorimeter during the LHC run 1
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2016 (English)In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 11, article id T10005Article in journal (Refereed) Published
Abstract [en]

This article describes the Laser calibration system of the ATLAS hadronic Tile Calorimeter that has been used during the run 1 of the LHC. First, the stability of the system associated readout electronics is studied. It is found to be stable with variations smaller than 0.6 %. Then, the method developed to compute the calibration constants, to correct for the variations of the gain of the calorimeter photomultipliers, is described. These constants were determined with a statistical uncertainty of 0.3 % and a systematic uncertainty of 0.2 % for the central part of the calorimeter and 0.5 % for the end-caps. Finally, the detection and correction of timing mis-configuration of the Tile Calorimeter using the Laser system are also presented.

Keywords
Detector alignment and calibration methods (lasers, sources, particle-beams), Calorimeters, Performance of High Energy Physics Detectors
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-136932 (URN)10.1088/1748-0221/11/10/T10005 (DOI)000387876400005 ()
Available from: 2016-12-30 Created: 2016-12-19 Last updated: 2022-03-23Bibliographically approved
Abulaiti, Y., Åkerstedt, H., Åsman, B., Bendtz, K., Bertoli, G., Bessidskaia Bylund, O., . . . Tylmad, M. (2015). Centrality and rapidity dependence of inclusive jet production in root(NN)-N-S=5.02 TeV proton-lead collisions with the ATLAS detector. Physics Letters B, 748, 392-413
Open this publication in new window or tab >>Centrality and rapidity dependence of inclusive jet production in root(NN)-N-S=5.02 TeV proton-lead collisions with the ATLAS detector
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2015 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 748, p. 392-413Article in journal (Refereed) Published
Abstract [en]

Measurements of the centrality and rapidity dependence of inclusive jet production in root(NN)-N-S = 5.02 TeV proton-lead (p + Pb) collisions and the jet cross-section in root s = 2.76 TeV proton-proton collisions are presented. These quantities are measured in datasets corresponding to an integrated luminosity of 27.8 nb(-1) and 4.0 pb(-1), respectively, recorded with the ATLAS detector at the Large Hadron Collider in 2013. The p + Pb collision centrality was characterised using the total transverse energy measured in the pseudorapidity interval -4.9 < eta < -3.2 in the direction of the lead beam. Results are presented for the double-differential per-collision yields as a function of jet rapidity and transverse momentum (p(T)) for minimum-bias and centrality-selected p + Pb collisions, and are compared to the jet rate from the geometric expectation. The total jet yield in minimum-bias events is slightly enhanced above the expectation in a p(T)-dependent manner but is consistent with the expectation within uncertainties. The ratios of jet spectra from different centrality selections show a strong modification of jet production at all p(T) at forward rapidities and for large pT at mid-rapidity, which manifests as a suppression of the jet yield in central events and an enhancement in peripheral events. These effects imply that the factorisation between hard and soft processes is violated at an unexpected level in proton-nucleus collisions. Furthermore, the modifications at forward rapidities are found to be a function of the total jet energy only, implying that the violations may have a simple dependence on the hard parton-parton kinematics.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-120888 (URN)10.1016/j.physletb.2015.07.023 (DOI)000359146200061 ()
Available from: 2016-06-30 Created: 2015-09-18 Last updated: 2022-03-23Bibliographically approved
Abulaiti, Y., Åkerstedt, H., Åsman, B., Bendtz, K., Bertoli, G., Bessidskaia Bylund, O., . . . Tylmad, M. (2015). Identification and energy calibration of hadronically decaying tau leptons with the ATLAS experiment in pp collisions at root s=8 TeV. European Physical Journal C, 75(7), Article ID 303.
Open this publication in new window or tab >>Identification and energy calibration of hadronically decaying tau leptons with the ATLAS experiment in pp collisions at root s=8 TeV
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2015 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 75, no 7, article id 303Article in journal (Refereed) Published
Abstract [en]

This paper describes the trigger and offline reconstruction, identification and energy calibration algorithms for hadronic decays of tau leptons employed for the data collected from pp collisions in 2012 with the ATLAS detector at the LHC center-of-mass energy root s = 8 TeV. The performance of these algorithms is measured in most cases with Z decays to tau leptons using the full 2012 dataset, corresponding to an integrated luminosity of 20.3 fb(-1). An uncertainty on the offline reconstructed tau energy scale of 2-4%, depending on transverse energy and pseudorapidity, is achieved using two independent methods. The offline tau identification efficiency is measured with a precision of 2.5% for hadronically decaying tau leptons with one associated track, and of 4% for the case of three associated tracks, inclusive in pseudorapidity and for a visible transverse energy greater than 20 GeV. For hadronic tau lepton decays selected by offline algorithms, the tau trigger identification efficiency is measured with a precision of 2-8%, depending on the transverse energy. The performance of the tau algorithms, both offline and at the trigger level, is found to be stable with respect to the number of concurrent proton-proton interactions and has supported a variety of physics results using hadronically decaying tau leptons at ATLAS.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-119561 (URN)10.1140/epjc/s10052-015-3500-z (DOI)000357317900001 ()
Available from: 2015-08-18 Created: 2015-08-17 Last updated: 2022-03-23Bibliographically approved
Abulaiti, Y., Åsman, B., Bendtz, K., Bessidskaia, O., Bohm, C., Clément, C., . . . Tylmad, M. (2015). Jet energy measurement and its systematic uncertainty in proton-proton collisions at root s=7 TeV with the ATLAS detector. European Physical Journal C, 75(1), Article ID 17.
Open this publication in new window or tab >>Jet energy measurement and its systematic uncertainty in proton-proton collisions at root s=7 TeV with the ATLAS detector
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2015 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 75, no 1, article id 17Article in journal (Refereed) Published
Abstract [en]

The jet energy scale (JES) and its systematic uncertainty are determined for jetsmeasured with the ATLAS detector using proton-proton collision data with a centre-of-mass energy of root s = 7 TeV corresponding to an integrated luminosity of 4.7 fb(-1). Jets are reconstructed from energy deposits forming topological clusters of calorimeter cells using the anti-kt algorithmwith distance parameters R = 0.4 or R = 0.6, and are calibrated using MC simulations. A residual JES correction is applied to account for differences between data and MC simulations. This correction and its systematic uncertainty are estimated using a combination of in situ techniques exploiting the transverse momentum balance between a jet and a reference object such as a photon or a Z boson, for 20 <= p(T)(jet) < 1000 GeV and pseudorapidities vertical bar eta vertical bar < 4.5. The effect of multiple proton-proton interactions is corrected for, and an uncertainty is evaluated using in situ techniques. The smallest JES uncertainty of less than 1% is found in the central calorimeter region (vertical bar eta vertical bar| < 1.2) for jets with 55 = p(T)(jet) < 500 GeV. For central jets at lower p(T), the uncertainty is about 3%. A consistent JES estimate is found using measurements of the calorimeter response of single hadrons in proton-proton collisions and test-beam data, which also provide the estimate for p(T)(jet) > 1 TeV. The calibration of forward jets is derived from dijet p(T) balance measurements. The resulting uncertainty reaches its largest value of 6% for low-p(T) jets at vertical bar eta vertical bar| = 4.5. Additional JES uncertainties due to specific event topologies, such as close-by jets or selections of event samples with an enhanced content of jets originating from light quarks or gluons, are also discussed. The magnitude of these uncertainties depends on the event sample used in a given physics analysis, but typically amounts to 0.5-3%.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-115458 (URN)10.1140/epjc/s10052-014-3190-y (DOI)000348991900001 ()
Note

AuthorCount:2934;

Available from: 2015-03-26 Created: 2015-03-24 Last updated: 2022-03-23Bibliographically approved
Abulaiti, Y., Åkerstedt, H., Åsman, B., Bendtz, K., Bertoli, G., Bessidskaia Bylund, O., . . . Tylmad, M. (2015). Measurement of the charge asymmetry in dileptonic decays of top quark pairs in pp collisions at root s=7 TeV using the ATLAS detector. Journal of High Energy Physics (JHEP) (5), Article ID 061.
Open this publication in new window or tab >>Measurement of the charge asymmetry in dileptonic decays of top quark pairs in pp collisions at root s=7 TeV using the ATLAS detector
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2015 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 5, article id 061Article in journal (Refereed) Published
Abstract [en]

A measurement of the top-antitop (t (t) over bar) charge asymmetry is presented using data corresponding to an integrated luminosity of 4.6 fb(-1) of LHC pp collisions at a centre-of-mass energy of 7 TeV collected by the ATLAS detector. Events with two charged leptons, at least two jets and large missing transverse momentum are selected. Two observables are studied: A(C)(ll) based on the identified charged leptons, and A(C)(t (t) over bar), based on the reconstructed t (t) over bar final state. The asymmetries are measured to be A(C)(ll) =0.024 +/- 0.015 (stat.) +/- 0.009 (syst.), A(C)(t (t) over bar) = 0.021 +/- 0.025 (stat.) +/- 0.017 (syst.). The measured values are in agreement with the Standard Model predictions.

Keywords
Hadron-Hadron Scattering, Top physics
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-119073 (URN)10.1007/JHEP05(2015)061 (DOI)000356951100004 ()
Available from: 2015-08-13 Created: 2015-07-27 Last updated: 2022-03-23Bibliographically approved
Abulaiti, Y., Åkerstedt, H., Åsman, B., Bendtz, K., Bertoli, G., Bessidskaia Bylund, O., . . . Tylmad, M. (2015). Measurement of the forward-backward asymmetry of electron and muon pair-production in pp collisions at root s=7 TeV with the ATLAS detector. Journal of High Energy Physics (JHEP) (9), Article ID 049.
Open this publication in new window or tab >>Measurement of the forward-backward asymmetry of electron and muon pair-production in pp collisions at root s=7 TeV with the ATLAS detector
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2015 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 9, article id 049Article in journal (Refereed) Published
Abstract [en]

This paper presents measurements from the ATLAS experiment of the forward-backward asymmetry in the reaction pp -> Z/gamma* -> l(+)l(-), with l being electrons or muons, and the extraction of the effective weak mixing angle. The results are based on the full set of data collected in 2011 in pp collisions at the LHC at root s = 7 TeV, corresponding to an integrated luminosity of 4.8 fb(-1). The measured asymmetry values are found to be in agreement with the corresponding Standard Model predictions. The combination of the muon and electron channels yields a value of the effective weak mixing angle of sin(2) theta(lept)(eff) = 0.2308 +/- 0.0005(stat.)+/- 0.0006(syst.)+/- 0.0009(PDF), where the first uncertainty corresponds to data statistics, the second to s ystematic effects and the third to knowledge of the parton density functions. This result agrees with the current world average from the Particle Data Group fit.

Keywords
Hadron-Hadron Scattering
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-123859 (URN)10.1007/JHEP09(2015)049 (DOI)000363537800001 ()
Available from: 2015-12-08 Created: 2015-12-08 Last updated: 2022-03-23Bibliographically approved
Abulaiti, Y., Åkerstedt, H., Åsman, B., Bendtz, K., Bertoli, G., Bessidskaia Bylund, O., . . . Tylmad, M. (2015). Measurement of the inclusive jet cross-section in proton-proton collisions at root s=7 TeV using 4.5 fb(-1) of data with the ATLAS detector. Journal of High Energy Physics (JHEP) (2), Article ID 153.
Open this publication in new window or tab >>Measurement of the inclusive jet cross-section in proton-proton collisions at root s=7 TeV using 4.5 fb(-1) of data with the ATLAS detector
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2015 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 2, article id 153Article in journal (Refereed) Published
Abstract [en]

The inclusive jet cross-section is measured in proton-proton collisions at a centre-of-mass energy of 7 TeV using a data set corresponding to an integrated luminosity of 4.5 fb(-1) collected with the ATLAS detector at the Large Hadron Collider in 2011. Jets are identified using the anti-k(t) algorithm with radius parameter values of 0.4 and 0.6. The double-differential cross-sections are presented as a function of the jet transverse momentum and the jet rapidity, covering jet transverse momenta from 100 GeV to 2 TeV. Next-to-leading-order QCD calculations corrected for non-perturbative effects and electroweak effects, as well as Monte Carlo simulations with next-to-leading-order matrix elements interfaced to parton showering, are compared to the measured cross-sections. A quantitative comparison of the measured cross-sections to the QCD calculations using several sets of parton distribution functions is performed.

Keywords
Hadron-Hadron Scattering
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-115913 (URN)10.1007/JHEP02(2015)153 (DOI)000350490700001 ()
Note

AuthorCount:2893;

Available from: 2015-04-17 Created: 2015-04-08 Last updated: 2022-03-23Bibliographically approved
Abulaiti, Y., Åkerstedt, H., Åsman, B., Bendtz, K., Bertoli, G., Bessidskaia, O., . . . Tylmad, M. (2015). Measurement of the production and lepton charge asymmetry of W bosons in Pb plus Pb collisions at root s(NN)=2.76 TeV with the ATLAS detector. European Physical Journal C, 75(1), Article ID 23.
Open this publication in new window or tab >>Measurement of the production and lepton charge asymmetry of W bosons in Pb plus Pb collisions at root s(NN)=2.76 TeV with the ATLAS detector
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2015 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 75, no 1, article id 23Article in journal (Refereed) Published
Abstract [en]

A measurement of W boson production in lead-lead collisions at root s(NN) = 2.76 TeV is presented. It is based on the analysis of data collected with the ATLAS detector at the LHC in 2011 corresponding to an integrated luminosity of 0.14 nb(-1) and 0.15 nb(-1) in the muon and electron decay channels, respectively. The differential production yields and lepton charge asymmetry are each measured as a function of the average number of participating nucleons < N-part > and absolute pseudorapidity of the charged lepton. The results are compared to predictions based on next-to-leading-order QCD calculations. These measurements are, in principle, sensitive to possible nuclear modifications to the parton distribution functions and also provide information on scaling of W boson production in multi-nucleon systems.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-115445 (URN)10.1140/epjc/s10052-014-3231-6 (DOI)000348992600002 ()
Note

AuthorCount:2891;

Available from: 2015-03-27 Created: 2015-03-24 Last updated: 2022-03-23Bibliographically approved
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