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Lundberg, Olof
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Publications (10 of 553) Show all publications
Abulaiti, Y., Åkerstedt, H., Bendtz, K., Bertoli, G., Bessidskaia Bylund, O., Bohm, C., . . . Wallängen, V. (2018). A search for pair-produced resonances in four-jet final states at root s=13 TeV with the ATLAS detector. European Physical Journal C, 78(3), Article ID 250.
Open this publication in new window or tab >>A search for pair-produced resonances in four-jet final states at root s=13 TeV with the ATLAS detector
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2018 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 78, no 3, article id 250Article in journal (Refereed) Published
Abstract [en]

A search for massive coloured resonances which are pair-produced and decay into two jets is presented. The analysis uses 36.7 fb(-1) of root s = 13 TeV pp collision data recorded by the ATLAS experiment at the LHC in 2015 and 2016. No significant deviation from the background prediction is observed. Results are interpreted in a SUSY simplified model where the lightest supersymmetric particle is the top squark, (t) over tilde, which decays promptly into two quarks through R-parity-violating couplings. Top squarks with masses in the range 100 GeV < m((T) over tilde) < 410 GeV are excluded at 95% confidence level. If the decay is into a b-quark and a light quark, a dedicated selection requiring two b-tags is used to exclude masses in the ranges 100 GeV < m((t) over tilde) < 470 GeV and 480 GeV < m(<(t)over tilde>) < 610 GeV. Additional limits are set on the pair-production of massive colour-octet resonances.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-156093 (URN)10.1140/epjc/s10052-018-5693-4 (DOI)000428180600005 ()
Available from: 2018-05-14 Created: 2018-05-14 Last updated: 2022-03-23Bibliographically approved
Abulaiti, Y., Åkerstedt, H., Bendtz, K., Bertoli, G., Bessidskaia Bylund, O., Bohm, C., . . . Wallängen, V. (2018). Angular analysis of B-d(0) -> K* mu(+)mu(-) decays in pp collisions at root s=8 TeV with the ATLAS detector. Journal of High Energy Physics (JHEP) (10), Article ID 047.
Open this publication in new window or tab >>Angular analysis of B-d(0) -> K* mu(+)mu(-) decays in pp collisions at root s=8 TeV with the ATLAS detector
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2018 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 10, article id 047Article in journal (Refereed) Published
Abstract [en]

An angular analysis of the decay B-d(0) -> K*mu(+)mu(-) is presented, based on proton-proton collision data recorded by the ATLAS experiment at the LHC. The study is using 20.3 fb(-1) of integrated luminosity collected during 2012 at centre-of-mass energy of root s = 8TeV. Measurements of the K* longitudinal polarisation fraction and a set of angular parameters obtained for this decay are presented. The results are compatible with the Standard Model predictions.

Keywords
Hadron-Hadron scattering (experiments)
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-161981 (URN)10.1007/JHEP10(2018)047 (DOI)000447258900001 ()
Available from: 2018-11-20 Created: 2018-11-20 Last updated: 2022-03-23Bibliographically approved
Abulaiti, Y., Åkerstedt, H., Bertoli, G., Bessidskaia Bylund, O., Bohm, C., Carney, R. M. D., . . . Wallängen, V. (2018). Measurement of dijet azimuthal decorrelations in pp collisions at root s=8 TeV with the ATLAS detector and determination of the strong coupling. Physical Review D: covering particles, fields, gravitation, and cosmology, 98(9), Article ID 092004.
Open this publication in new window or tab >>Measurement of dijet azimuthal decorrelations in pp collisions at root s=8 TeV with the ATLAS detector and determination of the strong coupling
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2018 (English)In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 98, no 9, article id 092004Article in journal (Refereed) Published
Abstract [en]

A measurement of the rapidity and transverse momentum dependence of dijet azimuthal decorrelations is presented, using the quantity R-Delta phi. The quantity R-Delta phi specifies the fraction of the inclusive dijet events in which the azimuthal opening angle of the two jets with the highest transverse momenta is less than a given value of the parameter Delta phi(max). The quantity R-Delta phi is measured in proton-proton collisions at root s = 8 TeV as a function of the dijet rapidity interval, the event total scalar transverse momentum, and Delta phi(max). The measurement uses an event sample corresponding to an integrated luminosity of 20.2 fb(-1) collected with the ATLAS detector at the CERN Large Hadron Collider. Predictions of a perturbative QCD calculation at next-to-leading order in the strong coupling with corrections for nonperturbative effects are compared to the data. The theoretical predictions describe the data in the whole kinematic region. The data are used to determine the strong coupling alpha(S) and to study its running for momentum transfers from 260 GeV to above 1.6 TeV. Analysis that combines data at all momentum transfers results in alpha(S) (m(Z)) = 0.1127(- 0.0027) (+0.0063).

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-162862 (URN)10.1103/PhysRevD.98.092004 (DOI)000449397700001 ()
Available from: 2018-12-28 Created: 2018-12-28 Last updated: 2022-03-23Bibliographically approved
Abulaiti, Y., Åkerstedt, H., Bertoli, G., Bessidskaia Bylund, O., Bohm, C., Carney, R. M. D., . . . Wallängen, V. (2018). Measurement of inclusive jet and dijet cross-sections in proton-proton collisions at root s=13 TeV with the ATLAS detector. Journal of High Energy Physics (JHEP) (5), Article ID 195.
Open this publication in new window or tab >>Measurement of inclusive jet and dijet cross-sections in proton-proton collisions at root s=13 TeV with the ATLAS detector
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2018 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 5, article id 195Article in journal (Refereed) Published
Abstract [en]

Inclusive jet and dijet cross-sections are measured in proton-proton collisions at a centre-of-mass energy of 13 TeV. The measurement uses a dataset with an integrated luminosity of 3.2 fb(-1) recorded in 2015 with the ATLAS detector at the Large Hadron Collider. Jets are identified using the anti-lit algorithm with a radius parameter value of R = 0.4. The inclusive jet cross-sections are measured double-differentially as a function of the jet transverse momentum, covering the range from 100 GeV to 3.5 TeV, and the absolute jet rapidity up to vertical bar y vertical bar = 3. The double-differential dijet production cross-sections are presented as a function of the dijet mass, covering the range from 300 GeV to 9 TeV, and the half absolute rapidity separation between the two leading jets within vertical bar y vertical bar < 3, y*, up to y* = 3. Next-to-leading-order, and next-to-next-to-leading-order for the inclusive jet measurement, perturbative QCD calculations corrected for non-perturbative and electroweak effects are compared to the measured cross-sections.

Keywords
Hadron-Hadron scattering (experiments)
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-157716 (URN)10.1007/JHEP05(2018)195 (DOI)000433979200001 ()
Available from: 2018-08-01 Created: 2018-08-01 Last updated: 2022-03-23Bibliographically approved
Abulaiti, Y., Åkerstedt, H., Bendtz, K., Bertoli, G., Bessidskaia Bylund, O., Bohm, C., . . . Wallängen, V. (2018). Measurement of jet fragmentation in 5.02 TeV proton-lead and proton-proton collisions with the ATLAS detector. Nuclear Physics A, 978, 65-106
Open this publication in new window or tab >>Measurement of jet fragmentation in 5.02 TeV proton-lead and proton-proton collisions with the ATLAS detector
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2018 (English)In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 978, p. 65-106Article in journal (Refereed) Published
Abstract [en]

A measurement of the fragmentation functions of jets into charged particles in p Pb collisions and pp collisions is presented. The analysis utilizes 28 nb(-1) of p Pb data and 26 pb(-1) of pp data, both at root(TN)-T-s= 5.02 TeV, collected in 2013 and 2015, respectively, with the ATLAS detector at the LHC. The measurement is reported in the centre-of-mass frame of the nucleon-nucleon system for jets in the rapidity range vertical bar y*vertical bar <1.6 and with transverse momentum 45 < p(T) < 260 GeV. Results are presented both as a function of the charged-particle transverse momentum and as a function of the longitudinal momentum fraction of the particle with respect to the jet. The pp fragmentation functions are compared with results from Monte Carlo event generators and two theoretical models. The ratios of the p +Pb to pp fragmentation functions are found to be consistent with unity.

Keywords
Relativistic heavy-ion collisions, Jets, Fragmentation into hadrons
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-161963 (URN)10.1016/j.nuclphysa.2018.07.006 (DOI)000446948800005 ()
Available from: 2018-11-12 Created: 2018-11-12 Last updated: 2022-03-23Bibliographically approved
Abulaiti, Y., Åkerstedt, H., Bertoli, G., Bessidskaia Bylund, O., Bohm, C., Carney, R. M. D., . . . Wallängen, V. (2018). Measurement of longitudinal flow decorrelations in Pb plus Pb collisions at root s(NN)=2.76 and 5.02 TeV with the ATLAS detector. European Physical Journal C, 78(2), Article ID 142.
Open this publication in new window or tab >>Measurement of longitudinal flow decorrelations in Pb plus Pb collisions at root s(NN)=2.76 and 5.02 TeV with the ATLAS detector
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2018 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 78, no 2, article id 142Article in journal (Refereed) Published
Abstract [en]

Measurements of longitudinal flow correlations are presented for charged particles in the pseudorapidity range vertical bar eta vertical bar < 2.4 using 7 mu b(-1) and 470 mu b(-1) of Pb+Pb collisions at root s(NN) = 2.76 and 5.02 TeV, respectively, recorded by the ATLAS detector at the LHC. It is found that the correlation between the harmonic flow coefficients v(n) measured in two separated eta intervals does not factorise into the product of single-particle coefficients, and this breaking of factorisation, or flow decorrelation, increases linearly with the eta separation between the intervals. The flow decorrelation is stronger at 2.76 TeVthan at 5.02 TeV. Higher-order moments of the correlations are also measured, and the corresponding linear coefficients for the kth-moment of the v(n) are found to be proportional to k for v(3), but not for v(2). The decorrelation effect is separated into contributions from the magnitude of v(n) and the event-plane orientation, each as a function of eta. These two contributions are found to be comparable. The longitudinal flow correlations are also measured between v(n) of different order in n. The decorrelations of v(2) and v(3) are found to be independent of each other, while the decorrelations of v(4) and v(5) are found to be driven by the nonlinear contribution from v(2)(2) and v(2)v(3), respectively.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-154586 (URN)10.1140/epjc/s10052-018-5605-7 (DOI)000425395800005 ()
Available from: 2018-04-06 Created: 2018-04-06 Last updated: 2022-03-23Bibliographically approved
Abulaiti, Y., Åkerstedt, H., Bertoli, G., Bessidskaia Bylund, O., Bohm, C., Carney, R. M. D., . . . Wallängen, V. (2018). Measurement of long-range multiparticle azimuthal correlations with the subevent cumulant method in pp and p plus Pb collisions with the ATLAS detector at the CERN Large Hadron Collider. Physical Review C: Covering Nuclear Physics, 97(2), Article ID 024904.
Open this publication in new window or tab >>Measurement of long-range multiparticle azimuthal correlations with the subevent cumulant method in pp and p plus Pb collisions with the ATLAS detector at the CERN Large Hadron Collider
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2018 (English)In: Physical Review C: Covering Nuclear Physics, ISSN 2469-9985, E-ISSN 2469-9993, Vol. 97, no 2, article id 024904Article in journal (Refereed) Published
Abstract [en]

A detailed study of multiparticle azimuthal correlations is presented using pp data at root s = 5.02 and 13 TeV, and p+Pb data at root s(NN) = 5.02 TeV, recorded with the ATLAS detector at the CERN Large Hadron Collider. The azimuthal correlations are probed using four-particle cumulants c(n){4} and flow coefficients v(n){4} = (-c(n){4})(1/4) for n = 2 and 3, with the goal of extracting long-range multiparticle azimuthal correlation signals and suppressing the short-range correlations. The values of c(n){4} are obtained as a function of the average number of charged particles per event, < N-ch >, using the recently proposed two-subevent and three-subevent cumulant methods, and compared with results obtained with the standard cumulant method. The standard method is found to be strongly biased by short-range correlations, which originate mostly from jetswith a positive contribution to c(n){4}. The threesubevent method, on the other hand, is found to be least sensitive to short-range correlations. The three-subevent method gives a negative c(2){4}, and therefore a well-defined v(2){4}, nearly independent of < N-ch >, which implies that the long-range multiparticle azimuthal correlations persist to events with low multiplicity. Furthermore, v(2){4} is found to be smaller than the v(2){2} measured using the two-particle correlation method, as expected for long-range collective behavior. Finally, the measured values of v(2){4} and v(2){2} are used to estimate the number of sources relevant for the initial eccentricity in the collision geometry. The results based on the subevent cumulant technique provide direct evidence, in small collision systems, for a long-range collectivity involving many particles distributed across a broad rapidity interval.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-153752 (URN)10.1103/PhysRevC.97.024904 (DOI)000424747000006 ()
Available from: 2018-03-27 Created: 2018-03-27 Last updated: 2022-03-23Bibliographically approved
Abulaiti, Y., Åkerstedt, H., Bendtz, K., Bertoli, G., Bessidskaia Bylund, O., Bohm, C., . . . Wallängen, V. (2018). Measurement of quarkonium production in proton-lead and proton-proton collisions at 5.02 TeV with the ATLAS detector. European Physical Journal C, 78(3), Article ID 171.
Open this publication in new window or tab >>Measurement of quarkonium production in proton-lead and proton-proton collisions at 5.02 TeV with the ATLAS detector
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2018 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 78, no 3, article id 171Article in journal (Refereed) Published
Abstract [en]

The modification of the production of J/psi, psi(2S), and gamma (nS) (n = 1, 2, 3) in p+Pb collisions with respect to their production in pp collisions has been studied. The p+Pb and pp datasets used in this paper correspond to integrated luminosities of 28 nb(-1) and 25 pb(-1) respectively, collected in 2013 and 2015 by the ATLAS detector at the LHC, both at a centre-of-mass energy per nucleon pair of 5.02 TeV. The quarkonium states are reconstructed in the dimuon decay channel. The yields of J/psi and psi(2S) are separated into prompt and non-prompt sources. The measured quarkonium differential cross sections are presented as a function of rapidity and transverse momentum, as is the nuclear modification factor, R-pPb for J/psi and psi (nS). No significant modification of the J/psi production is observed while gamma (nS) production is found to be suppressed at low transverse momentum in p+Pb collisions relative to pp collisions. The production of excited charmonium and bottomonium states is found to be suppressed relative to that of the ground states in central p+Pb collisions.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-154840 (URN)10.1140/epjc/s10052-018-5624-4 (DOI)000426836000001 ()
Available from: 2018-04-19 Created: 2018-04-19 Last updated: 2022-03-23Bibliographically approved
Abulaiti, Y., Åkerstedt, H., Bertoli, G., Bessidskaia Bylund, O., Bohm, C., Carney, R. M. D., . . . Wallängen, V. (2018). Measurement of tau polarisation in Z/gamma* -> tau tau decays in proton-proton collisions at root s=8 TeV with the ATLAS detector. European Physical Journal C, 78(2), Article ID 163.
Open this publication in new window or tab >>Measurement of tau polarisation in Z/gamma* -> tau tau decays in proton-proton collisions at root s=8 TeV with the ATLAS detector
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2018 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 78, no 2, article id 163Article in journal (Refereed) Published
Abstract [en]

This paper presents a measurement of the polarisation of tau leptons produced in Z/gamma* -> tau tau decays which is performed with a dataset of proton-proton collisions at root s = 8 TeV, corresponding to an integrated luminosity of 20.2 fb(-1) recorded with the ATLAS detector at the LHC in 2012. The Z/gamma* -> tau tau decays are reconstructed from a hadronically decaying tau lepton with a single charged particle in the final state, accompanied by a tau lepton that decays leptonically. The tau polarisation is inferred from the relative fraction of energy carried by charged and neutral hadrons in the hadronic tau decays. The polarisation is measured in a fiducial region that corresponds to the kinematic region accessible to this analysis. The tau polarisation extracted over the full phase space within the Z/gamma* mass range of 66 < mZ/gamma* < 116GeVis found to be P-tau = -0.14 +/- 0.02(stat)+/- 0.04(syst). It is in agreement with the Standard Model prediction of Pt = -0.1517 +/- 0.0019, which is obtained from the ALP-GEN event generator interfaced with the PYTHIA 6 parton shower modelling and the TAUOLA tau decay library.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-154848 (URN)10.1140/epjc/s10052-018-5619-1 (DOI)000426484600001 ()
Available from: 2018-04-19 Created: 2018-04-19 Last updated: 2022-03-23Bibliographically approved
Abulaiti, Y., Åkerstedt, H., Bertoli, G., Bessidskaia Bylund, O., Bohm, C., Carney, R. M. D., . . . Wallängen, V. (2018). Measurement of the cross section for isolated-photon plus jet production in pp collisions at root s=13 TeV using the ATLAS detector. Physics Letters B, 780, 578-602
Open this publication in new window or tab >>Measurement of the cross section for isolated-photon plus jet production in pp collisions at root s=13 TeV using the ATLAS detector
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2018 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 780, p. 578-602Article in journal (Refereed) Published
Abstract [en]

The dynamics of isolated-photon production in association with a jet in proton-proton collisions at a centre-of-mass energy of 13 TeV are studied with the ATLAS detector at the LHC using a dataset with an integrated luminosity of 3.2 fb(-1). Photons are required to have transverse energies above 125 GeV. Jets are identified using the anti-k(t) algorithm with radius parameter R = 0.4 and required to have transverse momenta above 100 GeV. Measurements of isolated-photon plus jet cross sections are presented as functions of the leading-photon transverse energy, the leading-jet transverse momentum, the azimuthal angular separation between the photon and the jet, the photon-jet invariant mass and the scattering angle in the photon-jet centre-of-mass system. Tree-level plus parton-shower predictions from SHERPA and PYTHIA as well as next-to-leading-order QCD predictions from JETPHOX and SHERPA are compared to the measurements.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-158195 (URN)10.1016/j.physletb.2018.03.035 (DOI)000432187800079 ()
Available from: 2018-07-23 Created: 2018-07-23 Last updated: 2022-03-23Bibliographically approved
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