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Aaboud, M., Kastanas, K. A., Jensen, B., Ohm, C., Ripellino, G., Sidebo, P. E., . . . 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
Astronomi, astrofysik och kosmologi
Identifikatorer
urn:nbn:se:kth:diva-244519 (URN)10.1140/epjc/s10052-019-6540-y (DOI)000457998500007 ()2-s2.0-85061187220 (Scopus ID)
Anmärkning

QC 20190403

Tillgänglig från: 2019-04-03 Skapad: 2019-04-03 Senast uppdaterad: 2019-04-04Bibliografiskt granskad
Balek, P., Balek, P., Jensen, B., Ohm, C., Ripellino, G., Sidebo, P. E., . . . 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.

Ort, förlag, år, upplaga, sidor
ELSEVIER SCIENCE BV, 2019
Nyckelord
xenon-xenon collisions, lead-lead collisions, charged-hadron production, nuclear modification factor
Nationell ämneskategori
Fusion, plasma och rymdfysik
Identifikatorer
urn:nbn:se:kth:diva-245161 (URN)10.1016/j.nuclphysa.2018.10.079 (DOI)000457515500128 ()
Anmärkning

QC 20190307

Tillgänglig från: 2019-03-07 Skapad: 2019-03-07 Senast uppdaterad: 2019-03-07Bibliografiskt granskad
Aaboud, M., Jensen, B., Ohm, C., Ripellino, G., Sidebo, P. E., Strandberg, J., . . . et al., . (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:kth:diva-255200 (URN)10.1103/PhysRevLett.122.231801 (DOI)000471988600003 ()2-s2.0-85067675453 (Scopus ID)
Anmärkning

QC 20190724

Tillgänglig från: 2019-07-24 Skapad: 2019-07-24 Senast uppdaterad: 2019-07-24Bibliografiskt granskad
Aaboud, M., Lund-Jensen, B., Ohm, C., Ripellino, G., Sidebo, P. E., Strandberg, J. & 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
Fysik
Identifikatorer
urn:nbn:se:kth:diva-254103 (URN)10.1007/JHEP05(2019)088 (DOI)000468428300001 ()
Anmärkning

QC 20190624

Tillgänglig från: 2019-06-24 Skapad: 2019-06-24 Senast uppdaterad: 2019-06-24Bibliografiskt granskad
Aaboud, M., Kastanas, K. A., Lund-Jensen, B., Ohm, C., Ripellino, G., Sidebo, P. E., . . . et al., . (2019). Comparison of Fragmentation Functions for Jets Dominated by Light Quarks and Gluons from pp and Pb plus Pb Collisions in ATLAS. Physical Review Letters, 123(4), Article ID 042001.
Öppna denna publikation i ny flik eller fönster >>Comparison of Fragmentation Functions for Jets Dominated by Light Quarks and Gluons from pp and Pb plus Pb Collisions in ATLAS
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2019 (Engelska)Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 123, nr 4, artikel-id 042001Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Charged-particle fragmentation functions for jets azimuthally balanced by a high-transverse-momentum, prompt, isolated photon are measured in 25 pb(-1) of pp and 0.49 nb(-1) of Pb + Pb collision data at 5.02 TeV per nucleon pair recorded with the ATLAS detector at the Large Hadron Collider. The measurements are compared to predictions of Monte Carlo generators and to measurements of inclusively selected jets. In pp collisions, a different jet fragmentation function in photon-tagged events from that in inclusive jet events arises from the difference in fragmentation between light quarks and gluons. The ratios of the fragmentation functions in Pb + Pb events to that in pp events are used to explore the parton color-charge dependence of jet quenching in the hot medium. In relatively peripheral collisions, fragmentation functions exhibit a similar modification pattern for photon-tagged and inclusive jets. However, photon-tagged jets are observed to have larger modifications than inclusive jets in central Pb + Pb events.

Ort, förlag, år, upplaga, sidor
American Physical Society, 2019
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:kth:diva-256030 (URN)10.1103/PhysRevLett.123.042001 (DOI)000476696300004 ()
Anmärkning

QC 20190816

Tillgänglig från: 2019-08-16 Skapad: 2019-08-16 Senast uppdaterad: 2019-08-16Bibliografiskt granskad
Aaboud, M., Lund-Jensen, B., Ohm, C., Ripellino, G., Sidebo, P. E. & Strandberg, J. (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
Astronomi, astrofysik och kosmologi
Identifikatorer
urn:nbn:se:kth:diva-254100 (URN)10.1007/JHEP05(2019)142 (DOI)000469453900001 ()
Anmärkning

QC 20190625

Tillgänglig från: 2019-06-25 Skapad: 2019-06-25 Senast uppdaterad: 2019-06-25Bibliografiskt granskad
Aaboud, M., Kastanas, K. A., Lund-Jensen, B., Ohm, C., Ripellino, G., Sidebo, P. E., . . . et al., . (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. Elsevier B.V.

Ort, förlag, år, upplaga, sidor
ELSEVIER SCIENCE BV, 2019
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:kth:diva-244090 (URN)10.1016/j.physletb.2018.11.065 (DOI)000457165400062 ()2-s2.0-85059588295 (Scopus ID)
Anmärkning

QC 20190219

Tillgänglig från: 2019-02-19 Skapad: 2019-02-19 Senast uppdaterad: 2019-02-19Bibliografiskt granskad
Aaboud, M., Kastanas, K. A., Jensen, B., Ohm, C., Ripellino, G., Sidebo, P. E., . . . et al., . (2019). Cross-section measurements of the Higgs boson decaying into a pair of tau-leptons in proton-proton collisions at root 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 tau-leptons in proton-proton collisions at root 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 -> tau tau 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 root s = 13 TeV. All combinations of leptonic (tau -> l v (v) over bar with l = e, mu) and hadronic (tau -> hadrons v) tau decays arc considered. The H -> tau tau 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 -> tau tau decays. Using the data taken at root s = 13 TeV, the total cross section in the H -> tau tau decay channel is measured to be 3.77(-0.59)(+0.60)(stat)(-0.74)(+0.87) (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 -> tau tau decay channel are determined separately for vector-boson-fusion production and gluon-gluon-fusion production to be sigma(VBF)(H -> tau tau) = 0.28 +/- 0.09 (stat)(-0.09)(+0.11) (syst) pb and sigma(ggF)(H -> tau tau) = 3.1 +/- 1.0 (stat)(-1.3)(+1.6) (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.

Ort, förlag, år, upplaga, sidor
AMER PHYSICAL SOC, 2019
Nationell ämneskategori
Astronomi, astrofysik och kosmologi
Identifikatorer
urn:nbn:se:kth:diva-251493 (URN)10.1103/PhysRevD.99.072001 (DOI)000464740700002 ()
Anmärkning

QC 20190515

Tillgänglig från: 2019-05-15 Skapad: 2019-05-15 Senast uppdaterad: 2019-05-15Bibliografiskt granskad
Steinberg, P., Jensen, B., Ohm, C., Ripellino, G., Sidebo, P. E., Strandberg, J., . . . et al., . (2019). Electromagnetic processes with quasireal photons in Pb plus Pb collisions: QED, QCD, and the QGP. Nuclear Physics A, 982, 259-262
Öppna denna publikation i ny flik eller fönster >>Electromagnetic processes with quasireal photons in Pb plus 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.

Ort, förlag, år, upplaga, sidor
ELSEVIER SCIENCE BV, 2019
Nationell ämneskategori
Subatomär fysik
Identifikatorer
urn:nbn:se:kth:diva-245157 (URN)10.1016/j.nuclphysa.2018.10.087 (DOI)000457515500050 ()2-s2.0-85060167400 (Scopus ID)
Anmärkning

QC 20190308

Tillgänglig från: 2019-03-08 Skapad: 2019-03-08 Senast uppdaterad: 2019-08-12Bibliografiskt granskad
Aaboud, M., Lund-Jensen, B., Ohm, C., Ripellino, G., Sidebo, P. E., Strandberg, J., . . . et al., . (2019). Electron and photon energy calibration with the ATLAS detector using 2015–2016 LHC proton-proton collision data. Journal of Instrumentation, 14
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. 14Artikel 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 (IOP), 2019
Nyckelord
Calorimeter methods; Pattern recognition, cluster finding, calibration and fitting methods; Performance of High Energy Physics Detectors
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:kth:diva-249928 (URN)10.1088/1748-0221/14/03/P03017 (DOI)000463330900005 ()
Anmärkning

QC 20190423

Tillgänglig från: 2019-04-23 Skapad: 2019-04-23 Senast uppdaterad: 2019-04-23Bibliografiskt granskad
Organisationer
Identifikatorer
ORCID-id: ORCID iD iconorcid.org/0000-0002-0299-8236

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