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Gradin, P. O. Joakim
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Publications (10 of 384) Show all publications
Aaboud, M., Asimakopoulou, E. M., Bergeås Kuutmann, E., Bokan, P., Brenner, R., Ekelöf, T., . . . Zwalinski, L. (2020). Combined measurements of Higgs boson production and decay using up to 80 fb(-1) of proton-proton collision data at root S=13 TeV collected with the ATLAS experiment. Physical Review D: covering particles, fields, gravitation, and cosmology, 101(1), Article ID 012002.
Open this publication in new window or tab >>Combined measurements of Higgs boson production and decay using up to 80 fb(-1) of proton-proton collision data at root S=13 TeV collected with the ATLAS experiment
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2020 (English)In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 101, no 1, article id 012002Article in journal (Refereed) Published
Abstract [en]

Combined measurements of Higgs boson production cross sections and branching fractions arc presented. The combination is based on the analyses of the Higgs boson decay modes H -> gamma gamma, ZZ*, WW*, tau tau, b (b) over bar, mu mu, searches for decays into invisible final states, and on measurements of off-shell Higgs boson production. Up to 79.8 fb(-1) of proton-proton collision data collected at root S = 13 TeV with the ATLAS detector are used. Results are presented for the gluon-gluon fusion and vector-boson fusion processes, and for associated production with vector bosons or top-quarks. The global signal strength is determined to be mu = 1.11(-0.08)(+0.09). The combined measurement yields an observed (expected) significance for the vector-boson fusion production process of 6.5 sigma (5.3 sigma). Measurements in kinematic regions defined within the simplified template cross section framework are also shown. The results are interpreted in terms of modifiers applied to the Standard Model couplings of the Higgs boson to other particles, and are used to set exclusion limits on parameters in two-Higgs-doublet models and in the simplified minimal supersynunetric Standard Model. No significant deviations from Standard Model predictions are observed.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2020
National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-403500 (URN)10.1103/PhysRevD.101.012002 (DOI)000505485600001 ()
Funder
Swedish Research CouncilEU, European Research CouncilEU, Horizon 2020Wallenberg Foundations
Note

For complete list of authors see http://dx.doi.org/10.1103/PhysRevD.101.012002

Available from: 2020-01-29 Created: 2020-01-29 Last updated: 2020-01-29Bibliographically approved
Aaboud, M., Asimakopoulou, E. M., Bergeås Kuutmann, E., Bokan, P., Brenner, R., Ekelöf, T., . . . Zwalinski, L. (2020). Fluctuations of anisotropic flow in Pb plus Pb collisions at root s(NN)=5.02 TeV with the ATLAS detector. Journal of High Energy Physics (JHEP) (1), Article ID 51.
Open this publication in new window or tab >>Fluctuations of anisotropic flow in Pb plus Pb collisions at root s(NN)=5.02 TeV with the ATLAS detector
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2020 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 1, article id 51Article in journal (Refereed) Published
Abstract [en]

Multi-particle azimuthal cumulants are measured as a function of centrality and transverse momentum using 470 mu b(-1) of Pb+Pb collisions at root s(NN) = 5.02TeV with the ATLAS detector at the LHC. These cumulants provide information on the event-by-event fluctuations of harmonic flow coefficients v(n) and correlated fluctuations between two harmonics v(n) and v(m). For the first time, a non-zero four-particle cumulant is observed for dipolar flow, v(1). The four-particle cumulants for elliptic flow, v(2), and triangular flow, v(3), exhibit a strong centrality dependence and change sign in ultra-central collisions. This sign change is consistent with significant non-Gaussian fluctuations in v(2) and v(3). The four-particle cumulant for quadrangular flow, v(4), is found to change sign in mid-central collisions. Correlations between two harmonics are studied with three- and four-particle mixed-harmonic cumulants, which indicate an anti-correlation between v(2) and v(3), and a positive correlation between v(2) and v(4). These correlations decrease in strength towards central collisions and either approach zero or change sign in ultra-central collisions. To investigate the possible flow fluctuations arising from intrinsic centrality or volume fluctuations, the results are compared between two different event classes used for centrality definitions. In peripheral and mid-central collisions where the cumulant signals are large, only small differences are observed. In ultra-central collisions, the differences are much larger and transverse momentum dependent. These results provide new information to disentangle flow fluctuations from the initial and final states, as well as new insights on the influence of centrality fluctuations.

Place, publisher, year, edition, pages
SPRINGER, 2020
Keywords
Hadron-Hadron scattering (experiments), Heavy-ion collision, Collective flow, Event-by-event fluctuation, Particle correlations and fluctuations
National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-407983 (URN)10.1007/JHEP01(2020)051 (DOI)000511969100001 ()
Funder
Swedish Research CouncilEU, European Research CouncilEU, Horizon 2020Wallenberg Foundations
Note

For complete list of authors see http://dx.doi.org/10.1007/JHEP01(2020)051

Available from: 2020-04-03 Created: 2020-04-03 Last updated: 2020-04-03Bibliographically approved
Aaboud, M., Asimakopoulou, E. M., Bergeås Kuutmann, E., Bokan, P., Brenner, R., Ekelöf, T., . . . Zwalinski, L. (2020). Measurement of Azimuthal Anisotropy of Muons from Charm and Bottom Hadrons in pp Collisions at root s=13 TeV with the ATLAS Detector. Physical Review Letters, 124(8), Article ID 082301.
Open this publication in new window or tab >>Measurement of Azimuthal Anisotropy of Muons from Charm and Bottom Hadrons in pp Collisions at root s=13 TeV with the ATLAS Detector
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2020 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 124, no 8, article id 082301Article in journal (Refereed) Published
Abstract [en]

The elliptic flow of muons from the decay of charm and bottom hadrons is measured in pp collisions at root s = 13 TeV using a data sample with an integrated luminosity of 150 pb(-1) recorded by the ATLAS detector at the LHC. The muons from heavy-flavor decay are separated from light-hadron decay muons using momentum imbalance between the tracking and muon spectrometers. The heavy-flavor decay muons are further separated into those from charm decay and those from bottom decay using the distance-of-closest-approach to the collision vertex. The measurement is performed for muons in the transverse momentum range 4-7 GeV and pseudorapidity range vertical bar eta vertical bar < 2.4. A significant nonzero elliptic anisotropy coefficient nu(2) is observed for muons from charm decays, while the nu(2) value for muons from bottom decays is consistent with zero within uncertainties.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2020
National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-407982 (URN)10.1103/PhysRevLett.124.082301 (DOI)000517288800010 ()32167369 (PubMedID)
Funder
Swedish Research CouncilEU, European Research CouncilEU, Horizon 2020Wallenberg Foundations
Note

For complete list of authors see http://dx.doi.org/10.1103/PhysRevLett.124.082301

Available from: 2020-04-03 Created: 2020-04-03 Last updated: 2020-04-03Bibliographically approved
Aaboud, M., Asimakopoulou, E. M., Bergeås Kuutmann, E., Bokan, P., Brenner, R., Ekelöf, T., . . . Zwalinski, L. (2020). Measurement of J/psi production in association with a W-+/- boson with pp data at 8 TeV. Journal of High Energy Physics (JHEP) (1), Article ID 95.
Open this publication in new window or tab >>Measurement of J/psi production in association with a W-+/- boson with pp data at 8 TeV
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2020 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 1, article id 95Article in journal (Refereed) Published
Abstract [en]

A measurement of the production of a prompt J/psi meson in association with a W-+/- boson with W-+/- -> mu nu and J/psi -> mu(+)mu(-) is presented for J/psi transverse momenta in the range 8.5-150 GeV and rapidity |y(J/psi)| < 2.1 using ATLAS data recorded in 2012 at the LHC. The data were taken at a proton-proton centre-of-mass energy of s = 8 TeV and correspond to an integrated luminosity of 20.3 fb(-1). The ratio of the prompt J/psi plus W-+/- cross-section to the inclusive W-+/- cross-section is presented as a differential measurement as a function of J/psi transverse momenta and compared with theoretical predictions using different double-parton-scattering cross-sections.

Place, publisher, year, edition, pages
SPRINGER, 2020
Keywords
Hadron-Hadron scattering (experiments)
National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-407462 (URN)10.1007/JHEP01(2020)095 (DOI)000511676700001 ()
Funder
Swedish Research CouncilEU, European Research CouncilEU, Horizon 2020
Note

For complete list of authors see http://dx.doi.org/10.1007/JHEP01(2020)095

Available from: 2020-03-26 Created: 2020-03-26 Last updated: 2020-03-26Bibliographically approved
Aaboud, M., Asimakopoulou, E. M., Bergeås Kuutmann, E., Bokan, P., Brenner, R., Ekelöf, T., . . . Zwalinski, L. (2020). Search for displaced vertices of oppositely charged leptons from decays of long-lived particles in pp collisions at root s=13 TeV with the ATLAS detector. Physics Letters B, 801, Article ID 135114.
Open this publication in new window or tab >>Search for displaced vertices of oppositely charged leptons from decays of long-lived particles in pp collisions at root s=13 TeV with the ATLAS detector
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2020 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 801, article id 135114Article in journal (Refereed) Published
Abstract [en]

A search for long-lived particles decaying into an oppositely charged lepton pair, mu mu, ee, or e mu, is presented using 32.8 fb(-1) of pp collision data collected at root s = 13 TeV by the ATLAS detector at the LHC. Candidate leptons are required to form a vertex, within the inner tracking volume of ATLAS, displaced from the primary pp interaction region. No lepton pairs with an invariant mass greater than 12 GeV are observed, consistent with the background expectations derived from data. The detection efficiencies for generic resonances with lifetimes (c tau) of 100-1000 mm decaying into a dilepton pair with masses between 0.1-1.0 TeV are presented as a function of p(T) and decay radius of the resonances to allow the extraction of upper limits on the cross sections for theoretical models. The result is also interpreted in a supersymmetric model in which the lightest neutralino, produced via squark-antisquark production, decays into l(+) l'(-) nu(l, l' = e, mu) with a finite lifetime due to the presence of R-parity violating couplings. Cross-section limits are presented for specific squark and neutralino masses. For a 700 GeV squark, neutralinos with masses of 50-500 GeV and mean proper lifetimes corresponding to c tau values between 1 mm to 6 m are excluded. For a 1.6 TeV squark, c tau values between 3 mm to 1 m are excluded for 1.3 TeV neutralinos.

Place, publisher, year, edition, pages
ELSEVIER, 2020
National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-406221 (URN)10.1016/j.physletb.2019.135114 (DOI)000508018500036 ()
Funder
Swedish Research CouncilEU, European Research CouncilEU, Horizon 2020Wallenberg Foundations
Note

For complete list of authors see http://dx.doi.org/10.1016/j.physletb.2019.135114

Available from: 2020-03-09 Created: 2020-03-09 Last updated: 2020-03-09Bibliographically approved
Aaboud, M., Asimakopoulou, E. M., Bergeås Kuutmann, E., Bokan, P., Brenner, R., Ekelöf, T., . . . Zwalinski, L. (2020). Search for electroweak production of charginos and sleptons decaying into final states with two leptons and missing transverse momentum in root s=13 TeV pp collisions using the ATLAS detector. European Physical Journal C, 80(2), Article ID 123.
Open this publication in new window or tab >>Search for electroweak production of charginos and sleptons decaying into final states with two leptons and missing transverse momentum in root s=13 TeV pp collisions using the ATLAS detector
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2020 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 80, no 2, article id 123Article in journal (Refereed) Published
Abstract [en]

A search for the electroweak production of charginos and sleptons decaying into final states with two electrons or muons is presented. The analysis is based on 139 fb(-1) of proton-proton collisions recorded by the ATLAS detector at the Large Hadron Collider at v s = 13 TeV. Three R-parity-conserving scenarios where the lightest neutralino is the lightest supersymmetric particle are considered: the production of chargino pairs with decays via eitherW bosons or sleptons, and the direct production of slepton pairs. The analysis is optimised for the first of these scenarios, but the results are also interpreted in the others. No significant deviations from the Standard Model expectations are observed and limits at 95% confidence level are set on the masses of relevant supersymmetric particles in each of the scenarios. For a massless lightest neutralino, masses up to 420 GeV are excluded for the production of the lightest-chargino pairs assuming W-boson-mediated decays and up to 1 TeV for slepton-mediated decays, whereas for slepton-pair production masses up to 700 GeV are excluded assuming three generations of mass-degenerate sleptons.

Place, publisher, year, edition, pages
SPRINGER, 2020
National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-407957 (URN)10.1140/epjc/s10052-019-7594-6 (DOI)000515792500002 ()
Funder
Swedish Research CouncilEU, European Research CouncilEU, Horizon 2020Wallenberg Foundations
Note

For complete list of authors see http://dx.doi.org/10.1140/epjc/s10052-019-7594-6

Available from: 2020-04-03 Created: 2020-04-03 Last updated: 2020-04-03Bibliographically approved
Aaboud, M., Asimakopoulou, E. M., Bergeås Kuutmann, E., Bokan, P., Brenner, R., Ekelöf, T., . . . Zwalinski, L. (2020). Search for non-resonant Higgs boson pair production in the bbl nu l nu final state with the ATLAS detector in pp collisions at root s=13 TeV. Physics Letters B, 801, Article ID 135145.
Open this publication in new window or tab >>Search for non-resonant Higgs boson pair production in the bbl nu l nu final state with the ATLAS detector in pp collisions at root s=13 TeV
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2020 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 801, article id 135145Article in journal (Refereed) Published
Abstract [en]

A search for non-resonant Higgs boson pair production, as predicted by the Standard Model, is presented, where one of the Higgs bosons decays via the H -> bb channel and the other via one of the H -> WW*/ZZ*/tau tau channels. The analysis selection requires events to have at least two b-tagged jets and exactly two leptons (electrons or muons) with opposite electric charge in the final state. Candidate events consistent with Higgs boson pair production are selected using a multi-class neural network discriminant. The analysis uses 139 fb(-1) of pp collision data recorded at a centre-of-mass energy of 13 TeV by the ATLAS detector at the Large Hadron Collider. An observed (expected) upper limit of 1.2 (0.9(-0.3)(+0.4)) pb is set on the non-resonant Higgs boson pair production cross-section at 95% confidence level, which is equivalent to 40 (29(-9)(+14)) times the value predicted in the Standard Model. 

Place, publisher, year, edition, pages
ELSEVIER, 2020
National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-406220 (URN)10.1016/j.physletb.2019.135145 (DOI)000508018500037 ()
Funder
Swedish Research CouncilEU, European Research CouncilEU, Horizon 2020Wallenberg Foundations
Note

For complete list of authors see http://dx.doi.org/10.1016/j.physletb.2019.135145

Available from: 2020-03-09 Created: 2020-03-09 Last updated: 2020-03-09Bibliographically approved
Aaboud, M., Asimakopoulou, E. M., Bergeås Kuutmann, E., Bokan, P., Brenner, R., Ekelöf, T., . . . Zwalinski, L. (2020). Search for the Higgs boson decays H -> ee and H -> e mu in pp collisions at root s=13 TeV with the ATLAS detector. Physics Letters B, 801, Article ID 135148.
Open this publication in new window or tab >>Search for the Higgs boson decays H -> ee and H -> e mu in pp collisions at root s=13 TeV with the ATLAS detector
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2020 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 801, article id 135148Article in journal (Refereed) Published
Abstract [en]

Searches for the Higgs boson decays H -> ee and H -> e mu are performed using data corresponding to an integrated luminosity of 139 fb(-1) collected with the ATLAS detector in pp collisions at root s = 13 TeV at the LHC. No significant signals are observed, in agreement with the Standard Model expectation. For a Higgs boson mass of 125 GeV, the observed (expected) upper limit at the 95% confidence level on the branching fraction B(H -> ee) is 3.6 x 10(-4) (3.5 x 10(-4)) and on B(H -> e mu) is 6.2 x 10(-5) (5.9 x 10(-5)). These results represent improvements by factors of about five and six on the previous best limits on B(H -> ee) and B(H -> e mu) respectively. 

Place, publisher, year, edition, pages
ELSEVIER, 2020
National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-406222 (URN)10.1016/j.physletb.2019.135148 (DOI)000508018500038 ()
Funder
Swedish Research CouncilEU, European Research CouncilEU, Horizon 2020Wallenberg Foundations
Note

For complete list of authors see http://dx.doi.org/10.1016/j.physletb.2019.135148

Available from: 2020-03-09 Created: 2020-03-09 Last updated: 2020-03-09Bibliographically approved
Aaboud, M., Asimakopoulou, E. M., Bergeås Kuutmann, E., Bokan, P., Brenner, R., Ekelöf, T., . . . Zwalinski, L. (2020). Transverse momentum and process dependent azimuthal anisotropies in root S-NN=8.16 TeV p plus Pb collisions with the ATLAS detector. European Physical Journal C, 80, Article ID 73.
Open this publication in new window or tab >>Transverse momentum and process dependent azimuthal anisotropies in root S-NN=8.16 TeV p plus Pb collisions with the ATLAS detector
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2020 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 80, article id 73Article in journal (Refereed) Published
Abstract [en]

The azimuthal anisotropy of charged particles produced in sNN=8.16TeV p+Pb collisions is measured with the ATLAS detector at the LHC. The data correspond to an integrated luminosity of 165 nb-1 that was collected in 2016. Azimuthal anisotropy coefficients, elliptic v2 and triangular v3\, extracted using two-particle correlations with a non-flow template fit procedure, are presented as a function of particle transverse momentum (pT) between 0.5 and 50 GeV. The v2 results are also reported as a function of centrality in three different particle pTintervals. The results are reported from minimum-bias events and jet-triggered events, where two jet pT thresholds are used. The anisotropies for particles with pT less than about 2 GeV are consistent with hydrodynamic flow expectations, while the significant non-zero anisotropies for pT in the range 9-50 GeV are not explained within current theoretical frameworks. In the pTrange 2-9 GeV, the anisotropies are larger in minimum-bias than in jet-triggered events. Possible origins of these effects, such as the changing admixture of particles from hard scattering and the underlying event, are discussed.

Place, publisher, year, edition, pages
SPRINGER, 2020
National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-407655 (URN)10.1140/epjc/s10052-020-7624-4 (DOI)000513720900001 ()
Funder
Swedish Research CouncilEU, European Research CouncilEU, Horizon 2020Wallenberg Foundations
Note

For complete list of authors see http://dx.doi.org/10.1140/epjc/s10052-020-7624-4

Available from: 2020-03-31 Created: 2020-03-31 Last updated: 2020-03-31Bibliographically approved
Aaboud, M., Asimakopoulou, E. M., Bergeås Kuutmann, E., Bokan, P., Brenner, R., Ekelöf, T., . . . Zwalinski, L. (2019). A strategy for a general search for new phenomena using data-derived signal regions and its application within the ATLAS experiment. European Physical Journal C, 79(2), Article ID 120.
Open this publication in new window or tab >>A strategy for a general search for new phenomena using data-derived signal regions and its application within the ATLAS experiment
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2019 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 79, no 2, article id 120Article in journal (Refereed) Published
Abstract [en]

This paper describes a strategy for a general search used by the ATLAS Collaboration to find potential indications of new physics. Events are classified according to their final state into many event classes. For each event class an automated search algorithm tests whether the data are compatible with the Monte Carlo simulated expectation in several distributions sensitive to the effects of new physics. The significance of a deviation is quantified using pseudo-experiments. A data selection with a significant deviation defines a signal region for a dedicated follow-up analysis with an improved background expectation. The analysis of the data-derived signal regions on a new dataset allows a statistical interpretation without the large look-elsewhere effect. The sensitivity of the approach is discussed using Standard Model processes and benchmark signals of new physics. As an example, results are shown for 3.2fb-1 of proton-proton collision data at a centre-of-mass energy of 13TeV collected with the ATLAS detector at the LHC in 2015, in which more than 700 event classes and more than 105 regions have been analysed. No significant deviations are found and consequently no data-derived signal regions for a follow-up analysis have been defined.

Place, publisher, year, edition, pages
SPRINGER, 2019
National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-378533 (URN)10.1140/epjc/s10052-019-6540-y (DOI)000457998500007 ()
Funder
Swedish Research Council
Note

For complete list of authors see http://dx.doi.org/10.1140/epjc/s10052-019-6540-y

Available from: 2019-03-22 Created: 2019-03-22 Last updated: 2019-03-22Bibliographically approved
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