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Johansson, Karl-Erik
Publications (10 of 88) Show all publications
Abulaiti, Y., Åsman, B., Bendtz, K., Bohm, C., Clément, C., Eriksson, D., . . . Yang, Z. (2014). Measurement of the inclusive isolated prompt photons cross section in pp collisions at root s=7 TeV with the ATLAS detector using 4.6 fb(-1). Physical Review D, 89(5), 052004
Open this publication in new window or tab >>Measurement of the inclusive isolated prompt photons cross section in pp collisions at root s=7 TeV with the ATLAS detector using 4.6 fb(-1)
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2014 (English)In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 89, no 5, p. 052004-Article in journal (Refereed) Published
Abstract [en]

A measurement of the cross section for the production of isolated prompt photons in pp collisions at a center-of-mass energy root s = 7 TeV is presented. The results are based on an integrated luminosity of 4.6 fb(-1) collected with the ATLAS detector at the LHC. The cross section is measured as a function of photon pseudorapidity eta(gamma) and transverse energy E-T(gamma) in the kinematic range 100 <= E-T(gamma) < 1000 GeV and in the regions vertical bar eta(gamma)vertical bar < 1.37 and 1.52 <= vertical bar eta(gamma)vertical bar < 2.37. The results are compared to leading-order parton-shower Monte Carlo models and next-to-leading-order perturbative QCD calculations. Next-to-leading-order perturbative QCD calculations agree well with the measured cross sections as a function of E-T(gamma) and eta(gamma) .

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-103986 (URN)10.1103/PhysRevD.89.052004 (DOI)000334304700002 ()
Note

AuthorCount:2916;

Available from: 2014-06-02 Created: 2014-05-27 Last updated: 2022-03-23Bibliographically approved
Abulaiti, Y., Åsman, B., Bendtz, K., Bessidskaia, O., Bohm, C., Clément, C., . . . Yang, Z. (2014). Search for new phenomena in photon plus jet events collected in proton-proton collisions at root s=8 TeV with the ATLAS detector. Physics Letters B, 728, 562-578
Open this publication in new window or tab >>Search for new phenomena in photon plus jet events collected in proton-proton collisions at root s=8 TeV with the ATLAS detector
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2014 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 728, p. 562-578Article in journal (Refereed) Published
Abstract [en]

This Letter describes a model-independent search for the production of new resonances in photon + jet (gamma + jet) events using 20 fb(-1) of proton-proton LHC data recorded with the ATLAS detector at a centre-of-mass energy of root s = 8 TeV. The gamma + jet mass distribution is compared to a background model fit from data; no significant deviation from the background-only hypothesis is found. Limits are set at 95% credibility level on generic Gaussian-shaped signals and two benchmark phenomena beyond the Standard Model: non-thermal quantum black holes and excited quarks. Non-thermal quantum black holes are excluded below masses of 4.6 TeV and excited quarks are excluded below masses of 3.5 TeV.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-102088 (URN)10.1016/j.physletb.2013.12.029 (DOI)000330556000086 ()
Note

AuthorCount:2923;

Available from: 2014-03-26 Created: 2014-03-26 Last updated: 2022-03-23Bibliographically approved
Åsman, B., Bendtz, K., Bohm, C., Clément, C., Eriksson, D., Gellerstedt, K., . . . Yang, Z. (2013). A search for high-mass resonances decaying to tau(+)tau(-) in pp collisions at root s=7 TeV with the ATLAS detector. Physics Letters B, 719(4-5), 242-260
Open this publication in new window or tab >>A search for high-mass resonances decaying to tau(+)tau(-) in pp collisions at root s=7 TeV with the ATLAS detector
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2013 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 719, no 4-5, p. 242-260Article in journal (Refereed) Published
Abstract [en]

This Letter presents a search for high-mass resonances decaying into tau(+)tau(-) final states using proton-proton collisions at root s = 7 TeV produced by the Large Hadron Collider. The data were recorded with the ATLAS detector and correspond to an integrated luminosity of 4.6 fb(-1). No statistically significant excess above the Standard Model expectation is observed; 95% credibility upper limits are set on the cross section times branching fraction of Z' resonances decaying into tau(+)tau(-) pairs as a function of the resonance mass. As a result, Z' bosons of the Sequential Standard Model with masses less than 1.40 TeV are excluded at 95% credibility.

Keywords
Exotics, Z ', Ditau, Resonance, Search
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-89527 (URN)10.1016/j.physletb.2013.01.040 (DOI)000315316900005 ()
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note

AuthorCount:2911;

Available from: 2013-05-03 Created: 2013-04-29 Last updated: 2022-03-23Bibliographically approved
Åsman, B., Bendtz, K., Bohm, C., Clément, C., Eriksson, D., Gellerstedt, K., . . . Yang, Z. (2013). A search for prompt lepton-jets in pp collisions at root s=7 TeV with the ATLAS detector. Physics Letters B, 719(4-5), 299-317
Open this publication in new window or tab >>A search for prompt lepton-jets in pp collisions at root s=7 TeV with the ATLAS detector
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2013 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 719, no 4-5, p. 299-317Article in journal (Refereed) Published
Abstract [en]

We present a search for a light (mass < 2 GeV) boson predicted by Hidden Valley supersymmetric models that decays into a final state consisting of collimated muons or electrons, denoted lepton-jets. The analysis uses 5 fb(-1) of root s = 7 TeV proton-proton collision data recorded by the ATLAS detector at the Large Hadron Collider to search for the following signatures: single lepton-jets with at least four muons; pairs of lepton-jets, each with two or more muons; and pairs of lepton-jets with two or more electrons. This study finds no statistically significant deviation from the Standard Model prediction and places 95% confidence-level exclusion limits on the production cross section times branching ratio of light bosons for several parameter sets of a Hidden Valley model.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-89525 (URN)10.1016/j.physletb.2013.01.034 (DOI)000315316900008 ()
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note

AuthorCount:2886;

Available from: 2013-05-03 Created: 2013-04-29 Last updated: 2022-03-23Bibliographically approved
Åsman, B., Bendtz, K., Bohm, C., Clément, C., Eriksson, D., Gellerstedt, K., . . . Yang, Z. (2013). ATLAS search for new phenomena in dijet mass and angular distributions using pp collisions at root s=7 TeV. Journal of High Energy Physics (JHEP) (1), 029
Open this publication in new window or tab >>ATLAS search for new phenomena in dijet mass and angular distributions using pp collisions at root s=7 TeV
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2013 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 1, p. 029-Article in journal (Refereed) Published
Abstract [en]

Mass and angular distributions of dijets produced in LHC proton-proton collisions at a centre-of-mass energy root s = 7TeV have been studied with the ATLAS detector using the full 2011 data set with an integrated luminosity of 4.8 fb(-1). Dijet masses up to similar to 4.0TeV have been probed. No resonance-like features have been observed in the dijet mass spectrum, and all angular distributions are consistent with the predictions of QCD. Exclusion limits on six hypotheses of new phenomena have been set at 95% CL in terms of mass or energy scale, as appropriate. These hypotheses include excited quarks below 2.83 TeV, colour octet scalars below 1.86TeV, heavy W bosons below 1.68 TeV, string resonances below 3.61 TeV, quantum black holes with six extra space-time dimensions for quantum gravity scales below 4.11 TeV, and quark contact interactions below a compositeness scale of 7.6 TeV in a destructive interference scenario.

Keywords
Hadron-Hadron Scattering
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-89251 (URN)10.1007/JHEP01(2013)029 (DOI)000315583200029 ()
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note

AuthorCount:2903;

Available from: 2013-04-17 Created: 2013-04-17 Last updated: 2022-03-23Bibliographically approved
Abulaiti, Y., Åsman, B., Bendtz, K., Bohm, C., Clément, C., Eriksson, D., . . . Yang, Z. (2013). Dynamics of isolated-photon plus jet production in pp collisions at root s=7 TeV with the ATLAS detector. Nuclear Physics B, 875(3), 483-535
Open this publication in new window or tab >>Dynamics of isolated-photon plus jet production in pp collisions at root s=7 TeV with the ATLAS detector
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2013 (English)In: Nuclear Physics B, ISSN 0550-3213, E-ISSN 1873-1562, Vol. 875, no 3, p. 483-535Article in journal (Refereed) Published
Abstract [en]

The dynamics of isolated-photon plus jet production in pp collisions at a centre-of-mass energy of 7 TeV has been studied with the ATLAS detector at the LHC using an integrated luminosity of 37 pb(-1). Measurements of isolated-photon plus jet bin-averaged cross sections are presented as functions of photon transverse energy, jet transverse momentum and jet rapidity. In addition, the bin-averaged cross sections as functions of the difference between the azimuthal angles of the photon and the jet, the photon jet invariant mass and the scattering angle in the photon jet centre-of-mass frame have been measured. Next-to-leading-order QCD calculations are compared to the measurements and provide a good description of the data, except for the case of the azimuthal opening angle.

Keywords
QCD, Photon, Jet
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-95073 (URN)10.1016/j.nuclphysb.2013.07.025 (DOI)000324601700001 ()2-s2.0-85042012072 (Scopus ID)
Projects
ATLAS Collaboration
Funder
Knut and Alice Wallenberg FoundationSwedish Research CouncilEU, European Research Council
Note

AuthorCount:2916;

Other Funding Agencies: 73 from various countries

Available from: 2013-10-23 Created: 2013-10-21 Last updated: 2022-10-06Bibliographically approved
Abulaiti, Y., Åsman, B., Bendtz, K., Bessidskaia, O., Bohm, C., Clément, C., . . . Yang, Z. (2013). Evidence for the spin-0 nature of the Higgs boson using ATLAS data. Physics Letters B, 726(1-3), 120-144
Open this publication in new window or tab >>Evidence for the spin-0 nature of the Higgs boson using ATLAS data
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2013 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 726, no 1-3, p. 120-144Article in journal (Refereed) Published
Abstract [en]

Studies of the spin and parity quantum numbers of the Higgs boson are presented, based on protonproton collision data collected by the ATLAS experiment at the LHC. The Standard Model spin-parity J(P) = 0(+) hypothesis is compared with alternative hypotheses using the Higgs boson decays H -> gamma gamma, H -> ZZ* -> 4l and H -> WW* -> l nu l nu, as well as the combination of these channels. The analysed dataset corresponds to an integrated luminosity of 20.7 fb(-1) collected at a centre-of-mass energy of root s = 8 TeV. For the H -> ZZ* -> 4l decay mode the dataset corresponding to an integrated luminosity of 4.6 fb(-1) collected at root s = 7 TeV is included. The data are compatible with the Standard Model J(P) = 0+ quantum numbers for the Higgs boson, whereas all alternative hypotheses studied in this Letter, namely some specific J(P) = 0(-), 1(+), 1(-), 2(+) models, are excluded at confidence levels above 97.8%. This exclusion holds independently of the assumptions on the coupling strengths to the Standard Model particles and in the case of the J(P) = 2(+) model, of the relative fractions of gluon-fusion and quark-antiquark production of the spin-2 particle. The data thus provide evidence for the spin-0 nature of the Higgs boson, with positive parity being strongly preferred.

Keywords
Higgs boson, Spin, Parity
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-100675 (URN)10.1016/j.physletb.2013.08.026 (DOI)000326482200015 ()
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note

AuthorCount:2922;

Available from: 2014-02-11 Created: 2014-02-10 Last updated: 2022-03-23Bibliographically approved
Åsman, B., Bendtz, K., Bohm, C., Clément, C., Eriksson, D., Gellerstedt, K., . . . Yang, Z. (2013). Improved luminosity determination in pp collisions at root s=7 TeV using the ATLAS detector at the LHC. European Physical Journal C, 73(8), 2518
Open this publication in new window or tab >>Improved luminosity determination in pp collisions at root s=7 TeV using the ATLAS detector at the LHC
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2013 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 73, no 8, p. 2518-Article in journal (Refereed) Published
Abstract [en]

The luminosity calibration for the ATLAS detector at the LHC during pp collisions at root s = 7 TeV in 2010 and 2011 is presented. Evaluation of the luminosity scale is performed using several luminosity-sensitive detectors, and comparisons are made of the long-term stability and accuracy of this calibration applied to the pp collisions at root s = 7 TeV. A luminosity uncertainty of delta L/L = +/- 3.5 % is obtained for the 47 pb(-1) of data delivered to ATLAS in 2010, and an uncertainty of delta L/L = +/- 1.8 % is obtained for the 5.5 fb(-1) delivered in 2011.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-94588 (URN)10.1140/epjc/s10052-013-2518-3 (DOI)000323901300010 ()
Note

AuthorCount:2912;

Available from: 2013-10-07 Created: 2013-10-07 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., Bendtz, K., Bohm, C., Clément, C., Eriksson, D., Gellerstedt, K., . . . Yang, Z. (2013). Jet energy resolution in proton-proton collisions at root s 7 TeV recorded in 2010 with the ATLAS detector. European Physical Journal C, 73(3), 2306
Open this publication in new window or tab >>Jet energy resolution in proton-proton collisions at root s 7 TeV recorded in 2010 with the ATLAS detector
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2013 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 73, no 3, p. 2306-Article in journal (Refereed) Published
Abstract [en]

The measurement of the jet energy resolution is presented using data recorded with the ATLAS detector in proton-proton collisions at root s = 7 TeV. The sample corresponds to an integrated luminosity of 35 pb(-1). Jets are reconstructed from energy deposits measured by the calorimeters and calibrated using different jet calibration schemes. The jet energy resolution is measured with two different in situ methods which are found to be in agreement within uncertainties. The total uncertainties on these measurements range from 20 % to 10 % for jets within vertical bar y vertical bar < 2.8 and with transverse momenta increasing from 30 GeV to 500 GeV. Overall, the Monte Carlo simulation of the jet energy resolution agrees with the data within 10 %.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-90797 (URN)10.1140/epjc/s10052-013-2306-0 (DOI)000318290600003 ()
Funder
Swedish Research Council
Note

AuthorCount:2877;

Available from: 2013-06-13 Created: 2013-06-11 Last updated: 2022-03-23Bibliographically approved
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