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Nordkvist, Björn
Publications (10 of 138) Show all publications
Åkerstedt, H., Bertoli, G., Bessidskaia Bylund, O., Bohm, C., Carney, R. M. D., Clement, C., . . . Wallängen, V. (2018). Operation and performance of the ATLAS Tile Calorimeter in Run 1. European Physical Journal C, 78(12), Article ID 987.
Open this publication in new window or tab >>Operation and performance of the ATLAS Tile Calorimeter in Run 1
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2018 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 78, no 12, article id 987Article in journal (Refereed) Published
Abstract [en]

The Tile Calorimeter is the hadron calorimeter covering the central region of the ATLAS experiment at the Large Hadron Collider. Approximately 10,000 photomultipliers collect light from scintillating tiles acting as the active material sandwiched between slabs of steel absorber. This paper gives an overview of the calorimeter's performance during the years 2008-2012 using cosmic-ray muon events and proton-proton collision data at centre-of-mass energies of 7 and 8 TeV with a total integrated luminosity of nearly 30 fb(-1). The signal reconstruction methods, calibration systems as well as the detector operation status are presented. The energy and time calibration methods performed excellently, resulting in good stability of the calorimeter response under varying conditions during the LHC Run 1. Finally, the Tile Calorimeter response to isolated muons and hadrons as well as to jets from proton-proton collisions is presented. The results demonstrate excellent performance in accord with specifications mentioned in the Technical Design Report.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-167704 (URN)10.1140/epjc/s10052-018-6374-z (DOI)000459286600002 ()30872953 (PubMedID)
Available from: 2019-04-12 Created: 2019-04-12 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
Åsman, B., Bohm, C., Clément, C., Eriksson, D., Gellerstedt, K., Hellman, S., . . . Yang, Z. (2013). Jet energy measurement with the ATLAS detector in proton-proton collisions at root s=7 TeV. European Physical Journal C, 73(3), 2304
Open this publication in new window or tab >>Jet energy measurement with the ATLAS detector in proton-proton collisions at root s=7 TeV
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2013 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 73, no 3, p. 2304-Article in journal (Refereed) Published
Abstract [en]

The jet energy scale and its systematic uncertainty are determined for jets measured with the ATLAS detector at the LHC in proton-proton collision data at a centre-of-mass energy of root s = 7 TeV corresponding to an integrated luminosity of 38 pb(-1). Jets are reconstructed with the anti-k(t) algorithm with distance parameters R = 0.4 or R = 0.6. Jet energy and angle corrections are determined from Monte Carlo simulations to calibrate jets with transverse momenta pT >= 20 GeV and pseudorapidities vertical bar eta vertical bar < 4.5. The jet energy systematic uncertainty is estimated using the single isolated hadron response measured in situ and in test-beams, exploiting the transverse momentum balance between central and forward jets in events with dijet topologies and studying systematic variations in Monte Carlo simulations. The jet energy uncertainty is less than 2.5 % in the central calorimeter region (vertical bar eta vertical bar < 0.8) for jets with 60 <= p(T) < 800 GeV, and is maximally 14 % for p(T) < 30 GeV in the most forward region 3.2 <= vertical bar eta vertical bar < 4.5. The jet energy is validated for jet transverse momenta up to 1 TeV to the level of a few percent using several in situ techniques by comparing a well-known reference such as the recoiling photon p(T), the sum of the transverse momenta of tracks associated to the jet, or a system of low-p(T) jets recoiling against a high-p(T) jet. More sophisticated jet calibration schemes are presented based on calorimeter cell energy density weighting or hadronic properties of jets, aiming for an improved jet energy resolution and a reduced flavour dependence of the jet response. The systematic uncertainty of the jet energy determined from a combination of in situ techniques is consistent with the one derived from single hadron response measurements over a wide kinematic range. The nominal corrections and uncertainties are derived for isolated jets in an inclusive sample of high-p(T) jets. Special cases such as event topologies with close-by jets, or selections of samples with an enhanced content of jets originating from light quarks, heavy quarks or gluons are also discussed and the corresponding uncertainties are determined.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-90795 (URN)10.1140/epjc/s10052-013-2304-2 (DOI)000318290600001 ()
Note

AuthorCount:3066;

Available from: 2013-06-13 Created: 2013-06-11 Last updated: 2022-03-23Bibliographically approved
Åsman, B., Bohm, C., Clément, C., Eriksson, D., Gellerstedt, K., Hellman, S., . . . Yang, Z. (2012). A Measurement of the Ratio of the W and Z Cross Sections with Exactly one Associated jet in pp Collisions at $\sqrt{s}=7$ TeV with ATLAS. Physics Letters B, 708, 221-240
Open this publication in new window or tab >>A Measurement of the Ratio of the W and Z Cross Sections with Exactly one Associated jet in pp Collisions at $\sqrt{s}=7$ TeV with ATLAS
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2012 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 708, p. 221-240Article in journal (Refereed) Published
Abstract [en]

The ratio of production cross sections of the W and Z bosons with exactly one associated jet is presented as a function of jet transverse momentum threshold. The measurement has been designed to maximise cancellation of experimental and theoretical uncertainties, and is reported both within a particle-level kinematic range corresponding to the detector acceptance and as a total cross-section ratio. Results are obtained with the ATLAS detector at the LHC in pp collisions at a centre-of-mass energy of 7 TeV using an integrated luminosity of 33 pb−1. The results are compared with perturbative leading-order, leading-log, and next-to-leading-order QCD predictions, and are found to agree within experimental and theoretical uncertainties. The ratio is measured for events with a single jet with pT>30 GeV to be 8.73±0.30(stat)±0.40(syst) in the electron channel, and 8.49±0.23(stat)±0.33(syst) in the muon channel.

Keywords
W boson, Z boson, Standard model, Perturbative QCD
National Category
Subatomic Physics
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-74256 (URN)10.1016/j.physletb.2012.01.042 (DOI)000301556500002 ()
Projects
Atlas
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note
Publikationen har totalt 3024 författare, G. Aad et al.Available from: 2012-03-03 Created: 2012-03-03 Last updated: 2022-03-23Bibliographically approved
Åsman, B., Bohm, C., Clément, C., Eriksson, D., Gellerstedt, K., Hellman, S., . . . Yang, Z. (2012). A study of the material in the ATLAS inner detector using secondary hadronic interactions. Journal of Instrumentation, 7, P01013
Open this publication in new window or tab >>A study of the material in the ATLAS inner detector using secondary hadronic interactions
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2012 (English)In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 7, p. P01013-Article in journal (Refereed) Published
Abstract [en]

The ATLAS inner detector is used to reconstruct secondary vertices due to hadronic interactions of primary collision products, so probing the location and amount of material in the inner region of ATLAS. Data collected in 7 TeV pp collisions at the LHC, with a minimum bias trigger, are used for comparisons with simulated events. The reconstructed secondary vertices have spatial resolutions ranging from similar to 200 mu m to 1 mm. The overall material description in the simulation is validated to within an experimental uncertainty of about 7%. This will lead to a better understanding of the reconstruction of various objects such as tracks, leptons, jets, and missing transverse momentum.

Keywords
Detector modelling and simulations I (interaction of radiation with matter, interaction, of photons with matter, interaction of hadrons with matter, etc), Particle tracking detectors (Solid-state detectors), Si microstrip and pad detectors, Large detector systems for particle and astroparticle physics
National Category
Subatomic Physics Accelerator Physics and Instrumentation
Identifiers
urn:nbn:se:su:diva-80308 (URN)10.1088/1748-0221/7/01/P01013 (DOI)000303806200127 ()
Note

AuthorCount:3017;

Available from: 2012-09-19 Created: 2012-09-17 Last updated: 2023-12-16Bibliographically approved
Åsman, B., Bohm, C., Clément, C., Eriksson, D., Gellerstedt, K., Hellman, S., . . . Yang, Z. (2012). Combined search for the Standard Model Higgs boson using up to 4.9 fb(-1) of pp collision data at root s=7 TeV with the ATLAS detector at the LHC. Physics Letters B, 710(1), 49-66
Open this publication in new window or tab >>Combined search for the Standard Model Higgs boson using up to 4.9 fb(-1) of pp collision data at root s=7 TeV with the ATLAS detector at the LHC
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2012 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 710, no 1, p. 49-66Article in journal (Refereed) Published
Abstract [en]

A combined search for the Standard Model Higgs boson with the ATLAS experiment at the LHC using datasets corresponding to integrated luminosities from 1.04 fb(-1) to 4.9 fb(-1) of pp collisions collected at root s = 7 TeV is presented. The Higgs boson mass ranges 112.9-115.5 GeV, 131-238 GeV and 251-466 GeV are excluded at the 95% confidence level (CL), while the range 124-519 GeV is expected to be excluded in the absence of a signal. An excess of events is observed around m(H) similar to 126 GeV with a local significance of 3.5 standard deviations (sigma). The local significances of H -> gamma, H -> ZZ(()*()) -> l(+)l(-)l'(+)l'(-) and H -> WW(*()) l(+)nu l'(-)(nu) over bar, the three most sensitive channels in this mass range, are 2.8 sigma, 2.1 sigma and 1.4 sigma. respectively. The global probability for the background to produce such a fluctuation anywhere in the explored Higgs boson mass range 110-600 GeV is estimated to be similar to 1.4% or, equivalently, 2.2 sigma.

National Category
Subatomic Physics
Identifiers
urn:nbn:se:su:diva-80294 (URN)10.1016/j.physletb.2012.02.044 (DOI)000302672500006 ()
Note

AuthorCount:3051;

Available from: 2012-09-25 Created: 2012-09-17 Last updated: 2024-02-28Bibliographically approved
Åsman, B., Bohm, C., Clément, C., Eriksson, D., Gellerstedt, K., Hellman, S., . . . Yang, Z. (2012). Determination of the Strange-Quark Density of the Proton from ATLAS Measurements of the W -> lv and Z -> ll Cross Sections. Physical Review Letters, 109(1), 012001
Open this publication in new window or tab >>Determination of the Strange-Quark Density of the Proton from ATLAS Measurements of the W -> lv and Z -> ll Cross Sections
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2012 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 109, no 1, p. 012001-Article in journal (Refereed) Published
Abstract [en]

AQCD analysis is reported of ATLAS data on inclusive W-+/- and Z boson production in pp collisions at the LHC, jointly with ep deep-inelastic scattering data from HERA. The ATLAS data exhibit sensitivity to the light quark sea composition and magnitude at Bjorken x similar to 0:01. Specifically, the data support the hypothesis of a symmetric composition of the light quark sea at low x. The ratio of the strange-to-down sea quark distributions is determined to be 1:00(-0:28)(+0.25) at absolute four-momentum transfer squared Q(2) = 1: 9 GeV2 and x = 0: 023.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-80160 (URN)10.1103/PhysRevLett.109.012001 (DOI)000306323400002 ()
Note

AuthorCount:3035;

Available from: 2012-09-13 Created: 2012-09-12 Last updated: 2022-03-23Bibliographically approved
Åsman, B., Bohm, C., Clément, C., Eriksson, D., Gellerstedt, K., Hellman, S., . . . Yang, Z. (2012). Electron performance measurements with the ATLAS detector using the 2010 LHC proton-proton collision data. European Physical Journal C, 72(3), 1909
Open this publication in new window or tab >>Electron performance measurements with the ATLAS detector using the 2010 LHC proton-proton collision data
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2012 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 72, no 3, p. 1909-Article in journal (Refereed) Published
Abstract [en]

Detailed measurements of the electron performance of the ATLAS detector at the LHC are reported, using decays of the Z, W and J/psi particles. Data collected in 2010 at root s = 7 TeV are used, corresponding to an integrated luminosity of almost 40 pb(-1). The inter-alignment of the inner detector and the electromagnetic calorimeter, the determination of the electron energy scale and resolution, and the performance in terms of response uniformity and linearity are discussed. The electron identification, reconstruction and trigger efficiencies, as well as the charge misidentification probability, are also presented.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-76294 (URN)10.1140/epjc/s10052-012-1909-1 (DOI)000302540000044 ()
Note

3029

Available from: 2012-05-11 Created: 2012-05-10 Last updated: 2022-03-23Bibliographically approved
Åsman, B., Bohm, C., Clément, C., Eriksson, D., Gellerstedt, K., Hellman, S., . . . Yang, Z. (2012). Forward-backward correlations and charged-particle azimuthal distributions in pp interactions using the ATLAS detector. Journal of High Energy Physics (JHEP) (7), 019
Open this publication in new window or tab >>Forward-backward correlations and charged-particle azimuthal distributions in pp interactions using the ATLAS detector
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2012 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 7, p. 019-Article in journal (Refereed) Published
Abstract [en]

Using inelastic proton-proton interactions at root s = 900 GeV and 7 TeV, recorded by the ATLAS detector at the LHC, measurements have been made of the correlations between forward and backward charged-particle multiplicities and, for the first time, between forward and backward charged-particle summed transverse momentum. In addition, jet-like structure in the events is studied by means of azimuthal distributions of charged particles relative to the charged particle with highest transverse momentum in a, selected kinematic region of the event. The results are compared with predictions from tunes of the PYTHIA and HERWIG++ Monte Carlo generators, which in most cases are found to provide a reasonable description of the data.

Keywords
Hadron-Hadron Scattering
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-81291 (URN)10.1007/JHEP07(2012)019 (DOI)000307298400019 ()
Note

AuthorCount:3034;

Available from: 2012-10-30 Created: 2012-10-15 Last updated: 2022-03-23Bibliographically approved
Åsman, B., Bohm, C., Clément, C., Eriksson, D., Gellerstedt, K., Hellman, S., . . . Yang, Z. (2012). Jet mass and substructure of inclusive jets in root s=7 TeV pp collisions with the ATLAS experiment. Journal of High Energy Physics (JHEP) (5), 128
Open this publication in new window or tab >>Jet mass and substructure of inclusive jets in root s=7 TeV pp collisions with the ATLAS experiment
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2012 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 5, p. 128-Article in journal (Refereed) Published
Abstract [en]

Recent studies have highlighted the potential of jet substructure techniques to identify the hadronic decays of boosted heavy particles. These studies all rely upon the assumption that the internal substructure of jets generated by QCD radiation is well understood. In this article, this assumption is tested on an inclusive sample of jets recorded with the ATLAS detector in 2010, which corresponds to 35 pb(-1) of pp collisions delivered by the LHC at root s = 7 TeV. In a subsample of events with single pp collisions, measurements corrected for detector efficiency and resolution are presented with full systematic uncertainties. Jet invariant mass, k(t) splitting scales and N-subjettiness variables are presented for anti-k(t) R = 1.0 jets and Cambridge-Aachen R = 1.2 jets. Jet invariant-mass spectra for Cambridge-Aachen R = 1.2 jets after a splitting and filtering procedure are also presented. Leading-order parton-shower Monte Carlo predictions for these variables are found to be broadly in agreement with data. The dependence of mean jet mass on additional pp interactions is also explored.

Keywords
Hadron-Hadron Scattering
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-80309 (URN)10.1007/JHEP05(2012)128 (DOI)000305238600048 ()
Note

AuthorCount:3058;

Available from: 2012-09-19 Created: 2012-09-17 Last updated: 2022-03-23Bibliographically approved
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