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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.
Öppna denna publikation i ny flik eller fönster >>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 (Engelska)Ingår i: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 79, nr 2, artikel-id 120Artikel i tidskrift (Refereegranskat) 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.

Ort, förlag, år, upplaga, sidor
SPRINGER, 2019
Nationell ämneskategori
Subatomär fysik
Identifikatorer
urn:nbn:se:uu:diva-378533 (URN)10.1140/epjc/s10052-019-6540-y (DOI)000457998500007 ()
Forskningsfinansiär
Vetenskapsrådet
Anmärkning

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

Tillgänglig från: 2019-03-22 Skapad: 2019-03-22 Senast uppdaterad: 2019-03-22Bibliografiskt granskad
Balek, P., Asimakopoulou, E. M., Bergeås Kuutmann, E., Bokan, P., Brenner, R., Ekelöf, T., . . . Zwalinski, L. (2019). Charged-hadron suppression in Pb plus Pb and Xe plus Xe collisions measured with the ATLAS detector. Nuclear Physics A, 982, 571-574
Öppna denna publikation i ny flik eller fönster >>Charged-hadron suppression in Pb plus Pb and Xe plus Xe collisions measured with the ATLAS detector
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2019 (Engelska)Ingår i: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 982, s. 571-574Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The ATLAS detector at the LHC recorded 0.49 nb(-1) of Pb+Pb collisions and 25 of pp(-1) collisions, both at the center-of-mass energy 5.02 TeV per nucleon pair. Recently, ATLAS also recorded 30 mu b(-1) of Xe+Xe collisions at the center-of-mass energy 5.44 TeV, which provides a new opportunity to study the system-size dependence of the charged-hadron production in heavy-ion collisions. The large acceptance of the ATLAS detector allows to measure the spectra of charged hadrons in a wide range of pseudorapidity and transverse momentum. The nuclear modification factors R-AA are constructed as a ratio of the spectra measured in Pb+Pb or Xe+Xe collisions to that measured in pp collisions. The R-AA obtained in the two systems are presented for different centrality intervals and the results are discussed.

Nyckelord
xenon-xenon collisions, lead-lead collisions, charged-hadron production, nuclear modification factor
Nationell ämneskategori
Subatomär fysik
Identifikatorer
urn:nbn:se:uu:diva-378203 (URN)10.1016/j.nuclphysa.2018.10.079 (DOI)000457515500128 ()
Anmärkning

For complete list of authors see http://dx.doi.org/10.1016/j.nuclphysa.2018.10.079

Tillgänglig från: 2019-03-05 Skapad: 2019-03-05 Senast uppdaterad: 2019-03-05Bibliografiskt granskad
Aaboud, M., Asimakopoulou, E. M., Bergeås Kuutmann, E., Bokan, P., Brenner, R., Ekelöf, T., . . . Zhang, Z. (2019). Combination of Searches for Invisible Higgs Boson Decays with the ATLAS Experiment. Physical Review Letters, 122(23), Article ID 231801.
Öppna denna publikation i ny flik eller fönster >>Combination of Searches for Invisible Higgs Boson Decays with the ATLAS Experiment
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2019 (Engelska)Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 122, nr 23, artikel-id 231801Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Dark matter particles, if sufficiently light, may be produced in decays of the Higgs boson. This Letter presents a statistical combination of searches for H -> invisible decays where H is produced according to the standard model via vector boson fusion, Z(ll)H, and W/Z(had)H, all performed with the ATLAS detector using 36.1 fb(-1) of pp collisions at a center-of-mass energy of root s = 13 TeV at the LHC. In combination with the results at root s = 7 and 8 TeV, an exclusion limit on the H -> invisible branching ratio of 0.26(0.17(-0.05)(+0.07)) at 95% confidence level is observed (expected).

Ort, förlag, år, upplaga, sidor
AMER PHYSICAL SOC, 2019
Nationell ämneskategori
Subatomär fysik
Identifikatorer
urn:nbn:se:uu:diva-390206 (URN)10.1103/PhysRevLett.122.231801 (DOI)000471988600003 ()31298882 (PubMedID)
Forskningsfinansiär
VetenskapsrådetEU, Europeiska forskningsrådetEU, Horisont 2020Wallenbergstiftelserna
Anmärkning

For complete list of authors see http://dx.doi.org/10.1103/PhysRevLett.122.231801

Tillgänglig från: 2019-08-09 Skapad: 2019-08-09 Senast uppdaterad: 2019-08-09Bibliografiskt granskad
Aaboud, M., Asimakopoulou, E. M., Bergeås Kuutmann, E., Bokan, P., Brenner, R., Ekelöf, T., . . . Woods, N. (2019). Combinations of single-top-quark production cross-section measurements and vertical bar f(LV)V(tb)vertical bar determinations at root s=7 and 8 TeV with the ATLAS and CMS experiments. Journal of High Energy Physics (JHEP) (5), Article ID 088.
Öppna denna publikation i ny flik eller fönster >>Combinations of single-top-quark production cross-section measurements and vertical bar f(LV)V(tb)vertical bar determinations at root s=7 and 8 TeV with the ATLAS and CMS experiments
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2019 (Engelska)Ingår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, nr 5, artikel-id 088Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

This paper presents the combinations of single-top-quark production cross-section measurements by the ATLAS and CMS Collaborations, using data from LHC proton-proton collisions at = 7 and 8 TeV corresponding to integrated luminosities of 1.17 to 5.1 fb(-1) at = 7 TeV and 12.2 to 20.3 fb(-1) at = 8 TeV. These combinations are performed per centre-of-mass energy and for each production mode: t-channel, tW, and s-channel. The combined t-channel cross-sections are 67.5 +/- 5.7 pb and 87.7 +/- 5.8 pb at = 7 and 8 TeV respectively. The combined tW cross-sections are 16.3 +/- 4.1 pb and 23.1 +/- 3.6 pb at = 7 and 8 TeV respectively. For the s-channel cross-section, the combination yields 4.9 +/- 1.4 pb at = 8 TeV. The square of the magnitude of the CKM matrix element V-tb multiplied by a form factor f(LV) is determined for each production mode and centre-of-mass energy, using the ratio of the measured cross-section to its theoretical prediction. It is assumed that the top-quark-related CKM matrix elements obey the relation |V-td|, |V-ts| << |V-tb|. All the |f(LV)V(tb)|(2) determinations, extracted from individual ratios at = 7 and 8 TeV, are combined, resulting in |f(LV)V(tb)| = 1.02 +/- 0.04 (meas.) +/- 0.02 (theo.). All combined measurements are consistent with their corresponding Standard Model predictions.

Ort, förlag, år, upplaga, sidor
SPRINGER, 2019
Nyckelord
Hadron-Hadron scattering (experiments)
Nationell ämneskategori
Subatomär fysik
Identifikatorer
urn:nbn:se:uu:diva-387959 (URN)10.1007/JHEP05(2019)088 (DOI)000468428300001 ()
Forskningsfinansiär
VetenskapsrådetEU, Europeiska forskningsrådetEU, Horisont 2020EU, Europeiska forskningsrådetEU, Horisont 2020, 675440EU, Europeiska forskningsrådetWallenbergstiftelserna
Anmärkning

For complete list of authors see http://dx.doi.org/10.1007/JHEP05(2019)088

Tillgänglig från: 2019-06-27 Skapad: 2019-06-27 Senast uppdaterad: 2019-06-27Bibliografiskt granskad
Aaboud, M., Asimakopoulou, E. M., Bergeås Kuutmann, E., Bokan, P., Brenner, R., Ekelöf, T., . . . Zwalinski, L. (2019). Constraints on mediator-based dark matter and scalar dark energy models using root s= 13 TeV pp collision data collected by the ATLAS detector. Journal of High Energy Physics (JHEP) (5), Article ID 142.
Öppna denna publikation i ny flik eller fönster >>Constraints on mediator-based dark matter and scalar dark energy models using root s= 13 TeV pp collision data collected by the ATLAS detector
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2019 (Engelska)Ingår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, nr 5, artikel-id 142Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Constraints on selected mediator-based dark matter models and a scalar dark energy model using up to 37 fb(-1) = 13 TeV pp collision data collected by the ATLAS detector at the LHC during 2015-2016 are summarised in this paper. The results of experimental searches in a variety of final states are interpreted in terms of a set of spin-1 and spin-0 single-mediator dark matter simplified models and a second set of models involving an extended Higgs sector plus an additional vector or pseudo-scalar mediator. The searches considered in this paper constrain spin-1 leptophobic and leptophilic mediators, spin-0 colour-neutral and colour-charged mediators and vector or pseudo-scalar mediators embedded in extended Higgs sector models. In this case, also = 8 TeV pp collision data are used for the interpretation of the results. The results are also interpreted for the first time in terms of light scalar particles that could contribute to the accelerating expansion of the universe (dark energy).

Ort, förlag, år, upplaga, sidor
SPRINGER, 2019
Nyckelord
Dark matter, Hadron-Hadron scattering (experiments)
Nationell ämneskategori
Subatomär fysik
Identifikatorer
urn:nbn:se:uu:diva-387956 (URN)10.1007/JHEP05(2019)142 (DOI)000469453900001 ()
Forskningsfinansiär
VetenskapsrådetEU, Europeiska forskningsrådetEU, Horisont 2020Wallenbergstiftelserna
Anmärkning

For complete list of authors see http://dx.doi.org/10.1007/JHEP05(2019)142

Tillgänglig från: 2019-06-27 Skapad: 2019-06-27 Senast uppdaterad: 2019-06-27Bibliografiskt granskad
Aaboud, M., Asimakopoulou, E. M., Bergeås Kuutmann, E., Bokan, P., Brenner, R., Ekelöf, T., . . . Zwalinski, L. (2019). Correlated long-range mixed-harmonic fluctuations measured in pp, p plus Pb and low-multiplicity Pb plus Pb collisions with the ATLAS detector. Physics Letters B, 789, 444-471
Öppna denna publikation i ny flik eller fönster >>Correlated long-range mixed-harmonic fluctuations measured in pp, p plus Pb and low-multiplicity Pb plus Pb collisions with the ATLAS detector
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2019 (Engelska)Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 789, s. 444-471Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Correlations of two flow harmonics v(n) and v(m) via three- and four-particle cumulants are measured in 13 TeV pp, 5.02 TeV p+Pb, and 2.76 TeV peripheral Pb+Pb collisions with the ATLAS detector at the LHC. The goal is to understand the multi-particle nature of the long-range collective phenomenon in these collision systems. The large non-flow background from dijet production present in the standard cumulant method is suppressed using a method of subevent cumulants involving two, three and four subevents separated in pseudorapidity. The results show a negative correlation between v(2) and v(3) and a positive correlation between v(2) and v(4) for all collision systems and over the full multiplicity range. However, the magnitudes of the correlations are found to depend on the event multiplicity, the choice of transverse momentum range and collision system. The relative correlation strength, obtained by normalisation of the cumulants with the < v(n)(2)> from a two-particle correlation analysis, is similar in the three collision systems and depends weakly on the event multiplicity and transverse momentum. These results based on the subevent methods provide strong evidence of a similar long-range multi-particle collectivity in pp, p+Pb and peripheral Pb+Pb collisions. (C) 2019 The Author. Published by Elsevier B.V.

Ort, förlag, år, upplaga, sidor
ELSEVIER SCIENCE BV, 2019
Nationell ämneskategori
Subatomär fysik
Identifikatorer
urn:nbn:se:uu:diva-377205 (URN)10.1016/j.physletb.2018.11.065 (DOI)000457165400062 ()
Forskningsfinansiär
VetenskapsrådetEU, Europeiska forskningsrådetEU, FP7, Sjunde ramprogrammetEU, Horisont 2020
Anmärkning

For complete list of authors see http://dx.doi.org/10.1016/j.physletb.2018.11.065

Tillgänglig från: 2019-02-15 Skapad: 2019-02-15 Senast uppdaterad: 2019-02-15Bibliografiskt granskad
Aaboud, M., Asimakopoulou, E. M., Bergeås Kuutmann, E., Bokan, P., Brenner, R., Ekelöf, T., . . . Zwalinski, L. (2019). Cross-section measurements of the Higgs boson decaying into a pair of τ-leptons in proton-proton collisions at √s=13 TeV with the ATLAS detector. Physical Review D: covering particles, fields, gravitation, and cosmology, 99(7), Article ID 072001.
Öppna denna publikation i ny flik eller fönster >>Cross-section measurements of the Higgs boson decaying into a pair of τ-leptons in proton-proton collisions at √s=13 TeV with the ATLAS detector
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2019 (Engelska)Ingår i: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 99, nr 7, artikel-id 072001Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

A measurement of production cross sections of the Higgs boson in proton-proton collisions is presented in the H → τ τ decay channel. The analysis is performed using 36.1 fb-1 of data recorded by the ATLAS experiment at the Large Hadron Collider at a center-of-mass energy of √s = 13 TeV. All combinations of leptonic (τ → l v v‾ with l = e, μ) and hadronic (τ→ hadrons v) τ decays arc considered. The H → τ τ signal over the expected background from other Standard Model processes is established with an observed (expected) significance of 4.4 (4.1) standard deviations. Combined with results obtained using data taken at 7 and 8 TeV center-of-mass energies, the observed (expected) significance amounts to 6.4 (5.4) standard deviations and constitutes an observation of H → τ τ decays. Using the data taken at √s = 13 TeV, the total cross section in the H → τ τ decay channel is measured to be 3.77+0.60-0.59(stat)+0.87-0.74 (syst) pb, for a Higgs boson of mass 125 GeV assuming the relative contributions of its production modes as predicted by the Standard Model. Total cross sections in the H → τ τ decay channel are determined separately for vector-boson-fusion production and gluon-gluon-fusion production to be σVBFH → τ τ = 0.28 ± 0.09 (stat)+0.11-0.09 (syst) pb and σggFH → τ τ = 3.1 ± 1.0 (stat)+1.6-1.3 (syst) pb, respectively. Similarly, results of a fit are reported in the framework of simplified template cross sections. All measurements are in agreement with Standard Model expectations.

Nationell ämneskategori
Subatomär fysik
Identifikatorer
urn:nbn:se:uu:diva-382859 (URN)10.1103/PhysRevD.99.072001 (DOI)000464740700002 ()
Forskningsfinansiär
VetenskapsrådetEU, Europeiska forskningsrådetEU, Horisont 2020Danmarks GrundforskningsfondNorges forskningsrådWallenbergstiftelsernaDeutsche Forschungsgemeinschaft (DFG)
Anmärkning

For complete list of authors see http://dx.doi.org/10.1103/PhysRevD.99.072001

Tillgänglig från: 2019-05-13 Skapad: 2019-05-13 Senast uppdaterad: 2019-05-13Bibliografiskt granskad
Steinberg, P., Asimakopoulou, E. M., Bergeås Kuutmann, E., Bokan, P., Brenner, R., Ekelöf, T., . . . Zwalinski, L. (2019). Electromagnetic processes with quasireal photons in Pb+Pb collisions: QED, QCD, and the QGP. Paper presented at XXVIIth International Conference on Ultrarelativistic Nucleus-Nucleus Collisions (Quark Matter 2018). Nuclear Physics A, 982, 259-262
Öppna denna publikation i ny flik eller fönster >>Electromagnetic processes with quasireal photons in Pb+Pb collisions: QED, QCD, and the QGP
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2019 (Engelska)Ingår i: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 982, s. 259-262Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Electromagnetic processes, both photon-photon and photon-nucleus, are shown to be useful in studying aspects of QED, QCD, and potentially the QGP. Using lead-lead collisions at root s(NN) = 5.02 TeV, the ATLAS detector has performed measurements of exclusive dimuon production, light-by-light scattering (via exclusive diphoton production), and photo-nuclear dijet production. These are all important examples of ultraperipheral collisions, where the nuclei do not interact hadronically. A recent study of the opening angles of dimuons produced in hadronic heavy-ion collisions, after subtracting heavy-flavor backgrounds, demonstrates that the dimuons carry information correlated with the overlap geometry, potentially about the density of charges in the QGP itself.

Nationell ämneskategori
Subatomär fysik
Identifikatorer
urn:nbn:se:uu:diva-378199 (URN)10.1016/j.nuclphysa.2018.10.087 (DOI)000457515500050 ()
Konferens
XXVIIth International Conference on Ultrarelativistic Nucleus-Nucleus Collisions (Quark Matter 2018)
Anmärkning

For complete list of authors see http://dx.doi.org/10.1016/j.nuclphysa.2018.10.087

Tillgänglig från: 2019-03-06 Skapad: 2019-03-06 Senast uppdaterad: 2019-03-06Bibliografiskt granskad
Aaboud, M., Asimakopoulou, E. M., Bergeås Kuutmann, E., Bokan, P., Brenner, R., Ekelöf, T., . . . Zwalinski, L. (2019). Electron and photon energy calibration with the ATLAS detector using 2015-2016 LHC proton-proton collision data. Journal of Instrumentation, 14, Article ID P03017.
Öppna denna publikation i ny flik eller fönster >>Electron and photon energy calibration with the ATLAS detector using 2015-2016 LHC proton-proton collision data
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2019 (Engelska)Ingår i: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 14, artikel-id P03017Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

This paper presents the electron and photon energy calibration obtained with the ATLAS detector using about 36 fb(-1) of LHC proton-proton collision data recorded at root s = 13 TeV in 2015 and 2016. The different calibration steps applied to the data and the optimization of the reconstruction of electron and photon energies are discussed. The absolute energy scale is set using a large sample of Z boson decays into electron-positron pairs. The systematic uncertainty in the energy scale calibration varies between 0.03% to 0.2% in most of the detector acceptance for electrons with transverse momentum close to 45 GeV. For electrons with transverse momentum of 10 GeV the typical uncertainty is 0.3% to 0.8% and it varies between 0.25% and 1% for photons with transverse momentum around 60 GeV. Validations of the energy calibration with J/psi -> e(+)e(-) decays and radiative Z boson decays are also presented.

Ort, förlag, år, upplaga, sidor
Institute of Physics Publishing (IOPP), 2019
Nyckelord
Calorimeter methods, Pattern recognition, cluster finding, calibration and fitting methods, Performance of High Energy Physics Detectors
Nationell ämneskategori
Subatomär fysik Acceleratorfysik och instrumentering
Identifikatorer
urn:nbn:se:uu:diva-382467 (URN)10.1088/1748-0221/14/03/P03017 (DOI)000463330900005 ()
Forskningsfinansiär
EU, Europeiska forskningsrådet
Anmärkning

For complete list of authors see http://dx.doi.org/10.1088/1748-0221/14/03/P03017

Tillgänglig från: 2019-05-02 Skapad: 2019-05-02 Senast uppdaterad: 2019-05-02Bibliografiskt granskad
Citron, Z., Asimakopoulou, E. M., Bergeås Kuutmann, E., Bokan, P., Brenner, R., Ekelöf, T., . . . Zwalinski, L. (2019). Electroweak probes of small and large systems with the ATLAS detector. Nuclear Physics A, 982, 603-606
Öppna denna publikation i ny flik eller fönster >>Electroweak probes of small and large systems with the ATLAS detector
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2019 (Engelska)Ingår i: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 982, s. 603-606Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Measurements of isolated prompt photon and massive electroweak (W and Z) boson production in different collision systems are of great interest to understand the partonic structure of heavy nuclei, and serve as a constraint on the initial state in larger collision systems. These channels are sensitive to a variety of effects such as the modification of the parton densities in nuclei in certain kinematic regions, and the energy loss of partons as they undergo multiple interactions in the nucleus before the hard parton-parton scattering. High-statistics samples of lead-lead and proton-lead collision data at root s(NN)=5.02 TeV and 8.16 TeV, respectively, taken by the ATLAS experiment at the LHC, as well as proton-proton comparison data at analogous collision energies, allow for a detailed study of these phenomena in data and comprehensive comparisons to the predictions of a variety of theoretical approaches. This paper presents the latest ATLAS results in these topics, including updated results on inclusive prompt photon production in proton-lead collisions over a broad kinematic range and high-precision W boson results in lead lead collisions.

Nyckelord
Lead-lead collisions, Proton-lead collisions, Proton-proton collisions, Photons, W boson, Z boson
Nationell ämneskategori
Subatomär fysik
Identifikatorer
urn:nbn:se:uu:diva-378205 (URN)10.1016/j.nuclphysa.2018.09.029 (DOI)000457515500136 ()
Anmärkning

For complete list of authors see http://dx.doi.org/10.1016/j.nuclphysa.2018.09.029

Tillgänglig från: 2019-03-05 Skapad: 2019-03-05 Senast uppdaterad: 2019-03-05Bibliografiskt granskad
Organisationer
Identifikatorer
ORCID-id: ORCID iD iconorcid.org/0000-0001-5265-3175

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