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Aaboud, M., Bergeås, E. K., Bokan, P., Brenner, R., Ekelöf, T., Ellert, M., . . . Zwalinski, L. (2018). Measurement of differential cross sections of isolated-photon plus heavy-flavour jet production in pp collisions at √s=8 TeV using the ATLAS detector. Physics Letters B, 776, 295-317
Open this publication in new window or tab >>Measurement of differential cross sections of isolated-photon plus heavy-flavour jet production in pp collisions at √s=8 TeV using the ATLAS detector
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2018 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 776, p. 295-317Article in journal (Refereed) Published
Abstract [en]

This Letter presents the measurement of differential cross sections of isolated prompt photons produced in association with a b-jet or a c-jet. These final states provide sensitivity to the heavy-flavour content of the proton and aspects related to the modelling of heavy-flavour quarks in perturbative QCD. The measurement uses proton-proton collision data at a centre-of-mass energy of 8 TeV recorded by the ATLAS detector at the LHC in 2012 corresponding to an integrated luminosity of up to 20.2 fb(-1). The differential cross sections are measured for each jet flavour with respect to the transverse energy of the leading photon in two photon pseudorapidity regions: vertical bar eta(gamma)vertical bar < 1.37 and 1.56 < vertical bar eta(gamma)vertical bar < 2.37. The measurement covers photon transverse energies 25 < E-T(gamma) < 400 GeV and 25 < E-T(gamma) < 350 GeV respectively for the two vertical bar eta(gamma)vertical bar regions. For each jet flavour, the ratio of the cross sections in the two vertical bar eta(gamma)vertical bar regions is also measured. The measurement is corrected for detector effects and compared to leading-order and next-to-leading-order perturbative QCD calculations, based on various treatments and assumptions about the heavy-flavour content of the proton. Overall, the predictions agree well with the measurement, but some deviations are observed at high photon transverse energies. The total uncertainty in the measurement ranges between 13% and 66%, while the central gamma+b measurement exhibits the smallest uncertainty, ranging from 13% to 27%, which is comparable to the precision of the theoretical predictions.

National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-345326 (URN)10.1016/j.physletb.2017.11.054 (DOI)000419641100043 ()
Funder
Swedish Research Council
Note

ATLAS Collaboration, for complete list of authors see https://doi.org/10.1016/j.physletb.2017.11.054

Available from: 2018-03-09 Created: 2018-03-09 Last updated: 2018-03-09Bibliographically approved
Aaboud, M., Bergeås, E. K., Bokan, P., Brenner, R., Ekelöf, T., Ellert, M., . . . Zwalinski, L. (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. 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. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, 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
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-348368 (URN)10.1103/PhysRevC.97.024904 (DOI)000424747000006 ()
Funder
Swedish Research CouncilEU, European Research CouncilEU, FP7, Seventh Framework ProgrammeEU, Horizon 2020German Research Foundation (DFG)European Science Foundation (ESF)Knut and Alice Wallenberg Foundation
Note

ATLAS Collaboration, for complete list of authors see https://doi.org/10.1103/PhysRevC.97.024904

Available from: 2018-04-12 Created: 2018-04-12 Last updated: 2018-04-12Bibliographically approved
Aaboud, M., Bergeås, E. K., Bokan, P., Brenner, R., Ekelöf, T., Ellert, M., . . . Zwalinski, L. (2018). Measurement of the cross-section for producing a W boson in association with a single top quark in pp collisions at √s=13 TeV with ATLAS. Journal of High Energy Physics (JHEP) (1), Article ID 063.
Open this publication in new window or tab >>Measurement of the cross-section for producing a W boson in association with a single top quark in pp collisions at √s=13 TeV with ATLAS
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2018 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 1, article id 063Article in journal (Refereed) Published
Abstract [en]

The inclusive cross-section for the associated production of a W boson and top quark is measured using data from proton-proton collisions at √s=13 TeV. The dataset corresponds to an integrated luminosity of 3.2 fb−1, and was collected in 2015 by the ATLAS detector at the Large Hadron Collider at CERN. Events are selected requiring two opposite sign isolated leptons and at least one jet; they are separated into signal and control regions based on their jet multiplicity and the number of jets that are identified as containing b hadrons. The W t signal is then separated from the t ($) over bar background using boosted decision tree discriminants in two regions. The cross-section is extracted by fitting templates to the data distributions, and is measured to be σ W t  = 94 ± 10(stat.) − 22 + 28 (syst.) ± 2(lumi.) pb. The measured value is in good agreement with the SM prediction of σtheory = 71.7±1.8 (scale)± 3.4 (PDF) pb [1].

Keyword
Hadron-Hadron scattering (experiments)
National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-345291 (URN)10.1007/JHEP01(2018)063 (DOI)000423212200001 ()
Funder
Swedish Research CouncilEU, European Research CouncilEU, FP7, Seventh Framework ProgrammeEU, Horizon 2020German Research Foundation (DFG)European Social Fund (ESF)
Note

ATLAS Collaboration, for complete list of authors see https://doi.org/10.1007/JHEP01(2018)063

Available from: 2018-03-09 Created: 2018-03-09 Last updated: 2018-03-09Bibliographically approved
Aaboud, M., Bergeås, E. K., Bokan, P., Brenner, R., Ekelöf, T., Ellert, M., . . . Zwalinski, L. (2018). Measurement of the exclusive gamma gamma -> mu(+)mu(-) process in proton-proton collisions at root s=13 TeV with the ATLAS detector. Physics Letters B, 777, 303-323
Open this publication in new window or tab >>Measurement of the exclusive gamma gamma -> mu(+)mu(-) process in proton-proton collisions at root s=13 TeV with the ATLAS detector
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2018 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 777, p. 303-323Article in journal (Refereed) Published
Abstract [en]

The production of exclusive gamma gamma -> mu(+)mu(-) events in proton-proton collisions at a centre-of-mass energy of 13 TeV is measured with the ATLAS detector at the LHC, using data corresponding to an integrated luminosity of 3.2 fb(-1). The measurement is performed for a dimuon invariant mass of 12 GeV < m(mu+mu-) < 70 GeV. The integrated cross-section is determined within a fiducial acceptance region of the ATLAS detector and differential cross-sections are measured as a function of the dimuon invariant mass. The results are compared to theoretical predictions both with and without corrections for absorptive effects.

Keyword
Hadron-Hadron scattering (experiments)
National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-346997 (URN)10.1016/j.physletb.2017.12.043 (DOI)000423930700041 ()
Funder
Swedish Research CouncilEU, European Research CouncilEU, FP7, Seventh Framework ProgrammeEU, Horizon 2020German Research Foundation (DFG)Knut and Alice Wallenberg Foundation
Note

ATLAS Collaboration, for complete list of authors see https://doi.org/10.1016/j.physletb.2017.12.043

Available from: 2018-03-23 Created: 2018-03-23 Last updated: 2018-03-23Bibliographically approved
Aaboud, M., Bergeås, E. K., Bokan, P., Brenner, R., Ekelöf, T., Ellert, M., . . . Zwalinski, L. (2018). Measurement of the W-boson mass in pp collisions at root s=7 TeV with the ATLAS detector. European Physical Journal C, 78, Article ID 110.
Open this publication in new window or tab >>Measurement of the W-boson mass in pp collisions at root s=7 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, article id 110Article in journal (Refereed) Published
Abstract [en]

A measurement of the mass of the W boson is presented based on proton-proton collision data recorded in 2011 at a centre-of-mass energy of 7 TeV with the ATLAS detector at the LHC, and corresponding to 4.6 fb(-1) of integrated luminosity. The selected data sample consists of 7.8 x 10(6) candidates in the W -> mu nu channel and 5.9 x 10(6) candidates in the W -> e nu channel. The W-boson mass is obtained from template fits to the reconstructed distributions of the charged lepton transverse momentum and of the W boson transverse mass in the electron and muon decay channels, yielding

m(W) = 80370 +/- 7 (stat.) +/- 11(exp. syst.)

+/- 14 (mod. syst.) MeV

= 80370 +/- 19 MeV,

where the first uncertainty is statistical, the second corresponds to the experimental systematic uncertainty, and the third to the physics-modelling systematic uncertainty. A measurement of the mass difference between the W+ and W- bosons yields m(W+) - m(W-) = -29 +/- 28 MeV.

National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-347255 (URN)10.1140/epjc/s10052-017-5475-4 (DOI)000424385500005 ()
Note

ATLAS Collaboration, for complete list of authors see http://dx.doi.org/10.1140/epjc/s10052-017-5475-4

Available from: 2018-03-28 Created: 2018-03-28 Last updated: 2018-03-28Bibliographically approved
Aaboud, M., Bergeås Kuutmann, E., Bokan, P., Brenner, R., Ekelöf, T., Ellert, M., . . . Zwalinski, L. (2018). Search for additional heavy neutral Higgs and gauge bosons in the ditau final state produced in 36 fb(-1) of pp collisions at root s=13 TeV with the ATLAS detector. Journal of High Energy Physics (JHEP), Article ID 55.
Open this publication in new window or tab >>Search for additional heavy neutral Higgs and gauge bosons in the ditau final state produced in 36 fb(-1) of pp 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, article id 55Article in journal (Refereed) Published
Abstract [en]

A search for heavy neutral Higgs bosons and Z' bosons is performed using a data sample corresponding to an integrated luminosity of 36.1 fb(-1) from proton-proton collisions at root s = 13 TeV recorded by the ATLAS detector at the LHC during 2015 and 2016. The heavy resonance is assumed to decay to tau(+)tau(-) with at least one tau lepton decaying to final states with hadrons and a neutrino. The search is performed in the mass range of 0.2-2.25 TeV for Higgs bosons and 0.2-4.0 TeV for Z' bosons. The data are in good agreement with the background predicted by the Standard Model. The results are interpreted in benchmark scenarios. In the context of the hMSSM scenario, the data exclude tan beta > 1.0 for m(A) = 0.25 TeV and tan beta > 42 for m(A) = 1.5 TeV at the 95% confidence level. For the Sequential Standard Model, Z'(SSM) with m(Z') < 2.42 TeV is excluded at 95% confidence level, while Z'(NU) with m(Z') < 2.25 TeV is excluded for the non-universal G(221) model that exhibits enhanced couplings to third-generation fermions.

Place, publisher, year, edition, pages
Springer, 2018
National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-343773 (URN)10.1007/JHEP01(2018)055 (DOI)000422669700003 ()
Note

ATLAS Collaboration, for complete list of authors see http://dx.doi.org/10.1007/JHEP01(2018)055

Available from: 2018-03-01 Created: 2018-03-01 Last updated: 2018-03-01Bibliographically approved
Aaboud, M., Bergeås, E. K., Bokan, P., Brenner, R., Ekelöf, T., Ellert, M., . . . Zwalinski, L. (2018). Search for an invisibly decaying Higgs boson or dark matter candidates produced in association with a Z boson in pp collisions at √s = 13 TeV with the ATLAS detector. Physics Letters B, 776, 318-337
Open this publication in new window or tab >>Search for an invisibly decaying Higgs boson or dark matter candidates produced in association with a Z boson in pp collisions at √s = 13 TeV with the ATLAS detector
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2018 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 776, p. 318-337Article in journal (Refereed) Published
Abstract [en]

A search for an invisibly decaying Higgs boson or dark matter candidates produced in association with a leptonically decaying Z boson in proton–proton collisions at √s = 13 TeV is presented. This search uses 36.1fb1 of data collected by the ATLAS experiment at the Large Hadron Collider. No significant deviation from the expectation of the Standard Model backgrounds is observed. Assuming the Standard Model ZH production cross-section, an observed (expected) upper limit of 67% (39%) at the 95% confidence level is set on the branching ratio of invisible decays of the Higgs boson with mass mH = 125 GeV. The corresponding limits on the production cross-section of the ZH process with the invisible Higgs boson decays are also presented. Furthermore, exclusion limits on the dark matter candidate and mediator masses are reported in the framework of simplified dark matter models.

National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-345334 (URN)10.1016/j.physletb.2017.11.049 (DOI)000419641100044 ()
Funder
Swedish Research CouncilEU, European Research CouncilEU, FP7, Seventh Framework ProgrammeEU, Horizon 2020German Research Foundation (DFG)European Science Foundation (ESF)
Note

ATLAS Collaboration, for complete list of authors see https://doi.org/10.1016/j.physletb.2017.11.049

Available from: 2018-03-09 Created: 2018-03-09 Last updated: 2018-03-09Bibliographically approved
Aaboud, M., Bergeås, E. K., Bokan, P., Brenner, R., Ekelöf, T., Ellert, M., . . . Zwalinski, L. (2018). Search for B - L R-parity-violating top squarks in root s=13 TeV pp collisions with the ATLAS experiment. Physical Review D. Particles and fields, 97, Article ID 032003.
Open this publication in new window or tab >>Search for B - L R-parity-violating top squarks in root s=13 TeV pp collisions with the ATLAS experiment
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2018 (English)In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 97, article id 032003Article in journal (Refereed) Published
Abstract [en]

A search is presented for the direct pair production of the stop, the supersymmetric partner of the top quark, that decays through an R-parity-violating coupling to a final state with two leptons and two jets, at least one of which is identified as a b-jet. The data set corresponds to an integrated luminosity of 36.1 fb(-1) of proton-proton collisions at a center-of-mass energy of root s = 13 TeV, collected in 2015 and 2016 by the ATLAS detector at the LHC. No significant excess is observed over the Standard Model background, and exclusion limits are set on stop pair production at a 95% confidence level. Lower limits on the stop mass are set between 600 GeV and 1.5 TeV for branching ratios above 10% for decays to an electron or muon and a b-quark.

National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-347243 (URN)10.1103/PhysRevD.97.032003 (DOI)000424190800001 ()
Funder
Swedish Research CouncilEU, European Research CouncilEU, FP7, Seventh Framework ProgrammeEU, Horizon 2020German Research Foundation (DFG)European Science Foundation (ESF)
Note

ATLAS Collaboration, for complete list of authors see https://doi.org/10.1103/PhysRevD.97.032003

Available from: 2018-03-28 Created: 2018-03-28 Last updated: 2018-03-28Bibliographically approved
Aaboud, M., Bergeås, E. K., Bokan, P., Brenner, R., Ekelöf, T., Ellert, M., . . . Zwalinski, L. (2018). Search for dark matter and other new phenomena in events with an energetic jet and large missing transverse momentum using the ATLAS detector. Journal of High Energy Physics (JHEP), Article ID 126.
Open this publication in new window or tab >>Search for dark matter and other new phenomena in events with an energetic jet and large missing transverse momentum using the ATLAS detector
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2018 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, article id 126Article in journal (Refereed) Published
Abstract [en]

Results of a search for new phenomena in final states with an energetic jet and large missing transverse momentum are reported. The search uses proton-proton collision data corresponding to an integrated luminosity of 36.1 fb(-1) at a centre-of-mass energy of 13 TeV collected in 2015 and 2016 with the ATLAS detector at the Large Hadron Collider. Events are required to have at least one jet with a transverse momentum above 250 GeV and no leptons (e or mu). Several signal regions are considered with increasing requirements on the missing transverse momentum above 250 GeV. Good agreement is observed between the number of events in data and Standard Model predictions. The results are translated into exclusion limits in models with pair-produced weakly interacting dark-matter candidates, large extra spatial dimensions, and supersymmetric particles in several compressed scenarios.

National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-346642 (URN)10.1007/JHEP01(2018)126 (DOI)000423443500001 ()
Funder
Swedish Research CouncilEU, European Research CouncilEU, FP7, Seventh Framework ProgrammeEU, Horizon 2020German Research Foundation (DFG)European Science Foundation (ESF)
Note

ATLAS Collaboration, for complete list of authors see https://doi.org/10.1007/JHEP01(2018)126

Available from: 2018-03-20 Created: 2018-03-20 Last updated: 2018-03-20Bibliographically approved
Aaboud, M., Bergeås Kuutmann, E., Bokan, P., Brenner, R., Ekelöf, T., Ellert, M., . . . Zwalinski, L. (2018). Search for dark matter produced in association with bottom or top quarks in root s=13 TeV pp collisions with the ATLAS detector. European Physical Journal C, 78(1), Article ID 18.
Open this publication in new window or tab >>Search for dark matter produced in association with bottom or top quarks in root s=13 TeV pp collisions 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 1, article id 18Article in journal (Refereed) Published
Abstract [en]

A search for weakly interacting massive dark matter particles produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and missing transverse momentum are considered. The analysis uses 36.1 fb(-1) of proton proton collision data recorded by the ATLAS experiment at root s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are interpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour-neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross-section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour-charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements.

Place, publisher, year, edition, pages
Springer, 2018
National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-343722 (URN)10.1140/epjc/s10052-017-5486-1 (DOI)000422660200005 ()
Note

ATLAS Collaboration, for complete list of authors see http://dx.doi.org/10.1140/epjc/s10052-017-5486-1

Available from: 2018-03-01 Created: 2018-03-01 Last updated: 2018-03-01Bibliographically approved
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