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Bessidskaia Bylund, Olga
Alternative names
Publications (10 of 513) Show all publications
Bertoli, G., Bessidskaia Bylund, O., Bohm, C., Carney, R. M. D., Clement, C., Gellerstedt, K., . . . Wallängen, V. (2020). Determination of jet calibration and energy resolution in proton-proton collisions at s=8 TeV using the ATLAS detector. European Physical Journal C, 80(12), Article ID 1104.
Open this publication in new window or tab >>Determination of jet calibration and energy resolution in proton-proton collisions at s=8 TeV 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 12, article id 1104Article in journal (Refereed) Published
Abstract [en]

The jet energy scale, jet energy resolution, and their systematic uncertainties are measured for jets reconstructed with the ATLAS detector in 2012 using proton-proton data produced at a centre-of-mass energy of 8 TeV with an integrated luminosity of 20 fb-1. Jets are reconstructed from clusters of energy depositions in the ATLAS calorimeters using the anti-kt algorithm. A jet calibration scheme is applied in multiple steps, each addressing specific effects including mitigation of contributions from additional proton-proton collisions, loss of energy in dead material, calorimeter non-compensation, angular biases and other global jet effects. The final calibration step uses several in situ techniques and corrects for residual effects not captured by the initial calibration. These analyses measure both the jet energy scale and resolution by exploiting the transverse momentum balance in gamma + jet, Z + jet, dijet, and multijet events. A statistical combination of these measurements is performed. In the central detector region, the derived calibration has a precision better than 1% for jets with transverse momentum 150 GeV<pT< 1500 GeV, and the relative energy resolution is (8.4 +/- 0.6)% for pT=100 GeV and (23 +/- 2)% for pT=20 GeV. The calibration scheme for jets with radius parameter R=1.0, for which jets receive a dedicated calibration of the jet mass, is also discussed.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-190699 (URN)10.1140/epjc/s10052-020-08477-8 (DOI)000598026400006 ()
Available from: 2021-03-03 Created: 2021-03-03 Last updated: 2022-02-25Bibliographically approved
Bertoli, G., Bessidskaia Bylund, O., Bohm, C., Carney, R. M. D., Clément, C., Gellerstedt, K., . . . Wallängen, V. (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.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-166542 (URN)10.1140/epjc/s10052-019-6540-y (DOI)000457998500007 ()
Available from: 2019-03-06 Created: 2019-03-06 Last updated: 2022-03-23Bibliographically approved
Bertoli, G., Bessidskaia Bylund, O., Bohm, C., Carney, R. M. D., Clement, C., Gellerstedt, K., . . . Wallängen, V. (2019). Search for doubly charged scalar bosons decaying into same-sign W boson pairs with the ATLAS detector. European Physical Journal C, 79(1), Article ID 58.
Open this publication in new window or tab >>Search for doubly charged scalar bosons decaying into same-sign W boson pairs with the ATLAS detector
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2019 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 79, no 1, article id 58Article in journal (Refereed) Published
Abstract [en]

A search for doubly charged scalar bosons decaying into W boson pairs is presented. It uses a data sample from proton-proton collisions corresponding to an integrated luminosity of 36.1fb-1 collected by the ATLAS detector at the LHC at a centre-of-mass energy of 13TeV in 2015 and 2016. This search is guided by a model that includes an extension of the Higgs sector through a scalar triplet, leading to a rich phenomenology that includes doubly charged scalar bosons H +/-+/-. Those bosons are produced in pairs in proton-proton collisions and decay predominantly into electroweak gauge bosons H +/-+/- W +/- W +/-. Experimental signatures with several leptons, missing transverse energy and jets are explored. No significant deviations from the Standard Model predictions are found. The parameter space of the benchmark model is excluded at 95% confidence level for H +/-+/- bosons with masses between 200 and 220 GeV.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-166796 (URN)10.1140/epjc/s10052-018-6500-y (DOI)000456628900001 ()
Available from: 2019-03-11 Created: 2019-03-11 Last updated: 2022-03-23Bibliographically approved
Bertoli, G., Bessidskaia Bylund, O., Bohm, C., Carney, R. M. D., Clement, C., Gellerstedt, K., . . . Wallängen, V. (2019). Search for invisible Higgs boson decays in vector boson fusion at root s=13 TeV with the ATLAS detector. Physics Letters B, 793, 499-519
Open this publication in new window or tab >>Search for invisible Higgs boson decays in vector boson fusion at root s=13 TeV with the ATLAS detector
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2019 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 793, p. 499-519Article in journal (Refereed) Published
Abstract [en]

We report a search for Higgs bosons that are produced via vector boson fusion and subsequently decay into invisible particles. The experimental signature is an energetic jet pair with invariant mass of O(1) TeVand O(100) GeVmissing transverse momentum. The analysis uses 36.1 fb(-1) of pp collision data at root s = 13 TeV recorded by the ATLAS detector at the LHC. In the signal region the 2252 observed events are consistent with the background estimation. Assuming a 125 GeV scalar particle with Standard Model cross sections, the upper limit on the branching fraction of the Higgs boson decay into invisible particles is 0.37 at 95% confidence level where 0.28 was expected. This limit is interpreted in Higgs portal models to set bounds on the wimp-nucleon scattering cross section. We also consider invisible decays of additional scalar bosons with masses up to 3 TeV for which the upper limits on the cross section times branching fraction are in the range of 0.3-1.7 pb.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-170080 (URN)10.1016/j.physletb.2019.04.024 (DOI)000470064800072 ()
Available from: 2019-07-08 Created: 2019-07-08 Last updated: 2022-03-23Bibliographically approved
Abulaiti, Y., Bertoli, G., Bessidskaia Bylund, O., Bohm, C., Carney, R. M. D., Clement, C., . . . Wallängen, V. (2019). Search for light resonances decaying to boosted quark pairs and produced in association with a photon or a jet in proton-proton collisions at root s=13 TeV with the ATLAS detector. Physics Letters B, 788, 316-335
Open this publication in new window or tab >>Search for light resonances decaying to boosted quark pairs and produced in association with a photon or a jet in proton-proton collisions at root s=13 TeV with the ATLAS detector
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2019 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 788, p. 316-335Article in journal (Refereed) Published
Abstract [en]

This Letter presents a search for new light resonances decaying to pairs of quarks and produced in association with a high-p(T) photon or jet. The dataset consists of proton-proton collisions with an integrated luminosity of 36.1 fb(-1) at a centre-of-mass energy of root s = 13 TeV recorded by the ATLAS detector at the Large Hadron Collider. Resonance candidates are identified as massive large-radius jets with substructure consistent with a particle decaying into a quark pair. The mass spectrum of the candidates is examined for local excesses above background. No evidence of a new resonance is observed in the data, which are used to exclude the production of a lepto-phobic axial-vector Z' boson.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-165672 (URN)10.1016/j.physletb.2018.09.062 (DOI)000455364400042 ()
Available from: 2019-02-06 Created: 2019-02-06 Last updated: 2022-03-23Bibliographically approved
Bertoli, G., Bessidskaia Bylund, O., Bohm, C., Carney, R. M. D., Clement, C., Gellerstedt, K., . . . Wallängen, V. (2019). Search for long-lived particles in final states with displaced dimuon vertices in pp collisions at root s=13 TeV with the ATLAS detector. Physical Review D: covering particles, fields, gravitation, and cosmology, 99(1), Article ID 012001.
Open this publication in new window or tab >>Search for long-lived particles in final states with displaced dimuon vertices in pp collisions at root s=13 TeV with the ATLAS detector
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2019 (English)In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 99, no 1, article id 012001Article in journal (Refereed) Published
Abstract [en]

A search is performed for a long-lived particle decaying into a final state that includes a pair of muons of opposite-sign electric charge, using proton-proton collision data collected at root s = 13 TeV by the ATLAS detector at the Large Hadron Collider corresponding to an integrated luminosity of 32.9 fb(-1). No significant excess over the Standard Model expectation is observed. Limits at 95% confidence level on the lifetime of the long-lived particle are presented in models of new phenomena including gauge-mediated supersymmetry or decay of the Higgs boson, H, to a pair of dark photons, Z(D). Lifetimes in the range c tau = 1-2400 cm are excluded, depending on the parameters of the model. In the supersymmetric model, the lightest neutralino is the next-to-lightest supersymmetric particle, with a relatively long lifetime due to its weak coupling to the gravitino, the lightest supersymmetric particle. The lifetime limits are determined for very light gravitino mass and various assumptions for the neutralino mass in the range 300-1000 GeV. In the dark photon model, the lifetime limits are interpreted as exclusion contours in the plane of the coupling between the Z(D) and the Standard Model Z boson versus the Z(D) mass (in the range 20-60 GeV), for various assumptions for the H -> Z(D)Z(D) branching fraction.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-165692 (URN)10.1103/PhysRevD.99.012001 (DOI)000454769000001 ()
Available from: 2019-02-05 Created: 2019-02-05 Last updated: 2022-03-23Bibliographically approved
Bertoli, G., Bessidskaia Bylund, O., Bohm, C., Carney, R. M. D., Clément, C., Gellerstedt, K., . . . Wallängen, V. (2019). Search for pair production of Higgs bosons in the b(b)over-barb(b)over-bar final state using proton-proton collisions at root s=13 TeV with the ATLAS detector. Journal of High Energy Physics (JHEP) (1), Article ID 030.
Open this publication in new window or tab >>Search for pair production of Higgs bosons in the b(b)over-barb(b)over-bar final state using proton-proton collisions at root s=13 TeV with the ATLAS detector
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2019 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 1, article id 030Article in journal (Refereed) Published
Abstract [en]

A search for Higgs boson pair production in the bbbb final state is carried out with up to 36.1 fb(-1) of LHC proton-proton collision data collected at s=13 TeV with the ATLAS detector in 2015 and 2016. Three benchmark signals are studied: a spin-2 graviton decaying into a Higgs boson pair, a scalar resonance decaying into a Higgs boson pair, and Standard Model non-resonant Higgs boson pair production. Two analyses are carried out, each implementing a particular technique for the event reconstruction that targets Higgs bosons reconstructed as pairs of jets or single boosted jets. The resonance mass range covered is 260-3000 GeV. The analyses are statistically combined and upper limits on the production cross section of Higgs boson pairs times branching ratio to bbbb are set in each model. No significant excess is observed; the largest deviation of data over prediction is found at a mass of 280 GeV, corresponding to 2.3 standard deviations globally. The observed 95% confidence level upper limit on the non-resonant production is 13 times the Standard Model prediction.

Keywords
Hadron-Hadron scattering (experiments)
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-165764 (URN)10.1007/JHEP01(2019)030 (DOI)000455324200001 ()
Available from: 2019-02-04 Created: 2019-02-04 Last updated: 2022-03-23Bibliographically approved
Bertoli, G., Bessidskaia Bylund, O., Bohm, C., Carney, R. M. D., Clément, C., Gellerstedt, K., . . . Wallängen, V. (2019). Search for pairs of highly collimated photon-jets in pp collisions at root s=13 TeV with the ATLAS detector. Physical Review D: covering particles, fields, gravitation, and cosmology, 99(1), Article ID 012008.
Open this publication in new window or tab >>Search for pairs of highly collimated photon-jets in pp collisions at root s=13 TeV with the ATLAS detector
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2019 (English)In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 99, no 1, article id 012008Article in journal (Refereed) Published
Abstract [en]

Results of a search for the pair production of photon-jets-collimated groupings of photons-in the ATLAS detector at the Large Hadron Collider are reported. Highly collimated photon-jets can arise from the decay of new, highly boosted particles that can decay to multiple photons collimated enough to be identified in the electromagnetic calorimeter as a single, photonlike energy cluster. Data from proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 36.7 fb(-1), were collected in 2015 and 2016. Candidate photon-jet pair production events are selected from those containing two reconstructed photons using a set of identification criteria much less stringent than that typically used for the selection of photons, with additional criteria applied to provide improved sensitivity to photon-jets. Narrow excesses in the reconstructed diphoton mass spectra are searched for. The observed mass spectra are consistent with the Standard Model background expectation. The results are interpreted in the context of a model containing a new, high-mass scalar particle with narrow width, X, that decays into pairs of photon-jets via new, light particles, a. Upper limits are placed on the cross section times the product of branching ratios sigma x B(X -> aa) x B(a -> gamma gamma)(2) for 200 GeV < m(X) < 2 TeV and for ranges of m(a) from a lower mass of 100 MeV up to between 2 and 10 GeV, depending upon m(X). Upper limits are also placed on sigma x B(X -> aa) x B(a -> 3 pi(0))(2) for the same range of m(X) and for ranges of m(a) from a lower mass of 500 MeV up to between 2 and 10 GeV.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-166594 (URN)10.1103/PhysRevD.99.012008 (DOI)000456035800008 ()
Available from: 2019-03-29 Created: 2019-03-29 Last updated: 2022-03-23Bibliographically approved
Bertoli, G., Bessidskaia Bylund, O., Bohm, C., Carney, R. M. D., Clément, C., Gellerstedt, K., . . . Wallängen, V. (2019). Search for squarks and gluinos in final states with hadronically decaying tau-leptons, jets, and missing transverse momentum using pp collisions at root s=13 TeV with the ATLAS detector. Physical Review D: covering particles, fields, gravitation, and cosmology, 99(1), Article ID 012009.
Open this publication in new window or tab >>Search for squarks and gluinos in final states with hadronically decaying tau-leptons, jets, and missing transverse momentum using pp collisions at root s=13 TeV with the ATLAS detector
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2019 (English)In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 99, no 1, article id 012009Article in journal (Refereed) Published
Abstract [en]

A search for supersymmetry in events with large missing transverse momentum, jets, and at least one hadronically decaying tau-lepton is presented. Two exclusive final states with either exactly one or at least two tau-leptons are considered. The analysis is based on proton-proton collisions at root s = 13 TeV corresponding to an integrated luminosity of 36.1 fb(-1) delivered by the Large Hadron Collider and recorded by the ATLAS detector in 2015 and 2016. No significant excess is observed over the Standard Model expectation. At 95% confidence level, model-independent upper limits on the cross section are set and exclusion limits are provided for two signal scenarios: a simplified model of gluino pair production with tau-rich cascade decays, and a model with gauge-mediated supersymmetry breaking (GMSB). In the simplified model, gluino masses up to 2000 GeV are excluded for low values of the mass of the lightest supersymmetric particle (LSP), while LSP masses up to 1000 GeV are excluded for gluino masses around 1400 GeV. In the GMSB model, values of the supersymmetry-breaking scale are excluded below 110 TeV for all values of tan beta in the range 2 <= tan beta <= 60, and below 120 TeV for tan beta > 30.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-166590 (URN)10.1103/PhysRevD.99.012009 (DOI)000456035800003 ()
Available from: 2019-03-04 Created: 2019-03-04 Last updated: 2022-03-23Bibliographically approved
Abulaiti, Y., Åkerstedt, H., Bendtz, K., Bertoli, G., Bessidskaia Bylund, O., Bohm, C., . . . Wallängen, V. (2018). A search for pair-produced resonances in four-jet final states at root s=13 TeV with the ATLAS detector. European Physical Journal C, 78(3), Article ID 250.
Open this publication in new window or tab >>A search for pair-produced resonances in four-jet final states at root s=13 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 250Article in journal (Refereed) Published
Abstract [en]

A search for massive coloured resonances which are pair-produced and decay into two jets is presented. The analysis uses 36.7 fb(-1) of root s = 13 TeV pp collision data recorded by the ATLAS experiment at the LHC in 2015 and 2016. No significant deviation from the background prediction is observed. Results are interpreted in a SUSY simplified model where the lightest supersymmetric particle is the top squark, (t) over tilde, which decays promptly into two quarks through R-parity-violating couplings. Top squarks with masses in the range 100 GeV < m((T) over tilde) < 410 GeV are excluded at 95% confidence level. If the decay is into a b-quark and a light quark, a dedicated selection requiring two b-tags is used to exclude masses in the ranges 100 GeV < m((t) over tilde) < 470 GeV and 480 GeV < m(<(t)over tilde>) < 610 GeV. Additional limits are set on the pair-production of massive colour-octet resonances.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-156093 (URN)10.1140/epjc/s10052-018-5693-4 (DOI)000428180600005 ()
Available from: 2018-05-14 Created: 2018-05-14 Last updated: 2022-03-23Bibliographically approved
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