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Aaboud, M., Bergeås Kuutmann, E., Bokan, R., Brenner, R., Ekelöf, T., Ellert, M., . . . Zwalinski, L. (2018). A search for resonances decaying into a Higgs boson and a new particle X in the XH -> qqbb final state with the ATLAS detector. Physics Letters B, 779, 24-45
Open this publication in new window or tab >>A search for resonances decaying into a Higgs boson and a new particle X in the XH -> qqbb final state with the ATLAS detector
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2018 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 779, p. 24-45Article in journal (Refereed) Published
Abstract [en]

A search for heavy resonances decaying into a Higgs boson (H) and a new particle (X) is reported, utilizing 36.1 fb(-1) of proton-proton collision data at root s = 13 TeV collected during 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. The particle Xis assumed to decay to a pair of light quarks, and the fully hadronic final state XH -> q (q) over bar 'b (b) over bar is analysed. The search considers the regime of high XH resonance masses, where the X and H bosons are both highly Lorentz-boosted and are each reconstructed using a single jet with large radius parameter. A two-dimensional phase space of XH mass versus X mass is scanned for evidence of a signal, over a range of XH resonance mass values between 1 TeV and 4 TeV, and for X particles with masses from 50 GeV to 1000 GeV. All search results are consistent with the expectations for the background due to Standard Model processes, and 95% CL upper limits are set, as a function of XH and X masses, on the production cross-section of the XH -> q (q) over bar 'b (b) over bar resonance.

National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-353207 (URN)10.1016/j.physletb.2018.01.042 (DOI)000429098900004 ()
Funder
Swedish Research CouncilEU, European Research CouncilEU, FP7, Seventh Framework ProgrammeEU, Horizon 2020
Note

For complete list of authors see http://dx.doi.org/10.1016/j.physletb.2018.01.042

Available from: 2018-06-13 Created: 2018-06-13 Last updated: 2018-06-13Bibliographically approved
Aaboud, M., Bergeås, E. K., Bokan, P., Brenner, R., Ekelöf, T., Ellert, M., . . . Zwalinski, L. (2018). Direct top-quark decay width measurement in the t(t)over-bar lepton plus jets channel at root s=8 TeV with the ATLAS experiment. European Physical Journal C, 78, Article ID 129.
Open this publication in new window or tab >>Direct top-quark decay width measurement in the t(t)over-bar lepton plus jets channel at root s=8 TeV with the ATLAS experiment
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2018 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 78, article id 129Article in journal (Refereed) Published
Abstract [en]

This paper presents a direct measurement of the decay width of the top quark using t (t) over bar events in the lepton+jets final state. The data sample was collected by the ATLAS detector at the LHC in proton-proton collisions at a centre-of-mass energy of 8 TeV and corresponds to an integrated luminosity of 20.2 fb(-1). The decay width of the top quark is measured using a template fit to distributions of kinematic observables associated with the hadronically and semileptonically decaying top quarks. The result, Gamma(t) = 1.76 +/- 0.33 (stat.) (+0.79)(-0.68) (syst.) GeV for a top-quark mass of 172.5 GeV, is consistent with the prediction of the Standard Model.

National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-349823 (URN)10.1140/epjc/s10052-018-5595-5 (DOI)000425393800001 ()
Funder
Swedish Research CouncilWallenberg FoundationsGerman Research Foundation (DFG)EU, European Research CouncilEU, Horizon 2020EU, FP7, Seventh Framework Programme
Note

ATLAS Collaboration. For a complete list of authors see: http://dx.doi.org/10.1140/epjc/s10052-018-5595-5

Available from: 2018-05-02 Created: 2018-05-02 Last updated: 2018-05-02Bibliographically approved
Aaboud, M., Bergeås Kuutmann, E., Bokan, P., Brenner, R., Ekelöf, T., Ellert, M., . . . Zwalinski, L. (2018). Evidence for the associated production of the Higgs boson and a top quark pair with the ATLAS detector. Physical Review D: covering particles, fields, gravitation, and cosmology, 97(7), Article ID 072003.
Open this publication in new window or tab >>Evidence for the associated production of the Higgs boson and a top quark pair with the ATLAS detector
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2018 (English)In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 97, no 7, article id 072003Article in journal (Refereed) Published
Abstract [en]

A search for the associated production of the Higgs boson with a top quark pair ((tt) over barH) is reported. The search is performed in multilepton final states using a data set corresponding to an integrated luminosity of 36.1 fb(-1) of proton-proton collision data recorded by the ATLAS experiment at a center-of-mass energy root s = 13 TeV at the Large Hadron Collider. Higgs boson decays to WW*, tau tau, and ZZ* are targeted. Seven final states, categorized by the number and flavor of charged-lepton candidates, are examined for the presence of the Standard Model Higgs boson with a mass of 125 GeVand a pair of top quarks. An excess of events over the expected background from Standard Model processes is found with an observed significance of 4.1 standard deviations, compared to an expectation of 2.8 standard deviations. The best fit for the (tt) over barH production cross section is sot (tt) over barH) = 790(-210)(+230) fb, in agreement with the Standard Model prediction of 507(-50)(+35) fb. The combination of this result with other t <overline> tH searches from the ATLAS experiment using the Higgs boson decay modes to b (b) over bar, gamma gamma and ZZ* -> 4l, has an observed significance of 4.2 standard deviations, compared to an expectation of 3.8 standard deviations. This provides evidence for the (tt) over barH production mode.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2018
National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-352483 (URN)10.1103/PhysRevD.97.072003 (DOI)000429456900001 ()
Funder
Swedish Research CouncilWallenberg Foundations
Note

For complete list of authors see http://dx.doi.org/10.1103/PhysRevD.97.072003

Available from: 2018-06-08 Created: 2018-06-08 Last updated: 2018-06-08Bibliographically approved
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 Kuutmann, E., Bokan, P., Brenner, R., Ekelöf, T., Ellert, M., . . . Zwalinski, L. (2018). Measurement of differential cross-sections of a single top quark produced in association with a W boson at √s=13TeV with ATLAS. European Physical Journal C, 78(3), Article ID 186.
Open this publication in new window or tab >>Measurement of differential cross-sections of a single top quark produced in association with a W boson at √s=13TeV with ATLAS
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2018 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 78, no 3, article id 186Article in journal (Refereed) Published
Abstract [en]

The differential cross-section for the production of a W boson in association with a top quark is measured for several particle-level observables. The measurements are performed using 36.1 fb(-1) of pp collision data collected with the ATLAS detector at the LHC in 2015 and 2016. Differential cross-sections are measured in a fiducial phase space defined by the presence of two charged leptons and exactly one jet matched to a b-hadron, and are normalised with the fiducial cross-section. Results are found to be in good agreement with predictions from several Monte Carlo event generators.

National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-350628 (URN)10.1140/epjc/s10052-018-5649-8 (DOI)000426840100001 ()
Funder
Swedish Research Council
Note

For complete list of authors see http://dx.doi.org/10.1140/epjc/s10052-018-5649-8

Available from: 2018-05-18 Created: 2018-05-18 Last updated: 2018-05-18Bibliographically approved
Aaboud, M., Bergeås, E. K., Bokan, P., Brenner, R., Ekelöf, T., Ellert, M., . . . Zwalinski, L. (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, 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, 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
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-349821 (URN)10.1140/epjc/s10052-018-5605-7 (DOI)000425395800005 ()
Funder
Swedish Research CouncilEU, European Research CouncilEU, FP7, Seventh Framework ProgrammeEU, Horizon 2020German Research Foundation (DFG)European Science Foundation (ESF)Wallenberg Foundations
Note

ATLAS Collaboration, for complete list of authors see https://doi.org/10.1140/epjc/s10052-018-5605-7

Available from: 2018-05-02 Created: 2018-05-02 Last updated: 2018-05-02Bibliographically 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 Kuutmann, E., Bokan, P., Brenner, R., Ekelöf, T., Ellert, M., . . . Zwalinski, L. (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
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-351101 (URN)10.1140/epjc/s10052-018-5624-4 (DOI)000426836000001 ()
Funder
Swedish Research CouncilGerman Research Foundation (DFG)EU, FP7, Seventh Framework ProgrammeEU, Horizon 2020European Regional Development Fund (ERDF)EU, European Research Council
Note

For complete list of authors see http://dx.doi.org/10.1140/epjc/s10052-018-5624-4

Available from: 2018-05-25 Created: 2018-05-25 Last updated: 2018-05-25Bibliographically approved
Aaboudd, M., Bergeås Kuutmann, E., Bokan, P., Brenner, R., Ekelöf, T., Ellert, M., . . . Zwalinski, L. (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
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-351275 (URN)10.1140/epjc/s10052-018-5619-1 (DOI)000426484600001 ()
Funder
Swedish Research Council
Note

For complete list of authors see http://dx.doi.org/10.1140/epjc/s10052-018-5619-1

Available from: 2018-05-22 Created: 2018-05-22 Last updated: 2018-05-22Bibliographically 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
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ORCID iD: ORCID iD iconorcid.org/0000-0003-2887-5311

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