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BETA
Kastanas, Konstatinos A.ORCID iD iconorcid.org/0000-0001-6945-1916
Alternative names
Publications (10 of 174) Show all publications
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.
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.

Place, publisher, year, edition, pages
SPRINGER, 2019
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-244519 (URN)10.1140/epjc/s10052-019-6540-y (DOI)000457998500007 ()2-s2.0-85061187220 (Scopus ID)
Note

QC 20190403

Available from: 2019-04-03 Created: 2019-04-03 Last updated: 2019-04-04Bibliographically approved
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
Open this publication in new window or tab >>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 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 789, p. 444-471Article in journal (Refereed) 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.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2019
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-244090 (URN)10.1016/j.physletb.2018.11.065 (DOI)000457165400062 ()2-s2.0-85059588295 (Scopus ID)
Note

QC 20190219

Available from: 2019-02-19 Created: 2019-02-19 Last updated: 2019-02-19Bibliographically approved
Aaboud, M., Kastanas, K. A., Jensen, B., Ohm, C., Ripellino, G., Sidebo, P. E., . . . Zwalinski, L. (2019). In situ calibration of large-radius jet energy and mass in 13TeVproton-proton collisions with the ATLAS detector. European Physical Journal C, 79(2), Article ID 135.
Open this publication in new window or tab >>In situ calibration of large-radius jet energy and mass in 13TeVproton-proton collisions 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 2, article id 135Article in journal (Refereed) Published
Abstract [en]

The response of the ATLAS detector to large-radius jets is measured in situ using 36.2 fb(-1) of root s = 13TeV proton-proton collisions provided by the LHC and recorded by the ATLAS experiment during 2015 and 2016. The jet energy scale is measured in events where the jet recoils against a reference object, which can be either a calibrated photon, a reconstructed Z boson, or a system of well-measured small-radius jets. The jet energy resolution and a calibration of forward jets are derived using dijet balance measurements. The jet mass response is measured with two methods: using mass peaks formed by W bosons and top quarks with large transverse momenta and by comparing the jet mass measured using the energy deposited in the calorimeter with that using the momenta of charged-particle tracks. The transverse momentum and mass responses in simulations are found to be about 2-3% higher than in data. This difference is adjusted for with a correction factor. The results of the different methods are combined to yield a calibration over a large range of transverse momenta (p(T)). The precision of the relative jet energy scale is 1-2% for 200 GeV < p(T) < TeV, while that of the mass scale is 2-10%. The ratio of the energy resolutions in data and simulation is measured to a precision of 10-15% over the same p(T) range.

Place, publisher, year, edition, pages
SPRINGER, 2019
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-245136 (URN)10.1140/epjc/s10052-019-6632-8 (DOI)000458691000004 ()2-s2.0-85061476087 (Scopus ID)
Note

QC 20190307

Available from: 2019-03-07 Created: 2019-03-07 Last updated: 2019-03-07Bibliographically approved
Aaboud, M., Kastanas, K. A., Lund-Jensen, B., Ohm, C., Ripellino, G., Sidebo, P. E., . . . et al., . (2019). Measurement of photon-jet transverse momentum correlations in 5.02 TeV Pb + Pb and pp collisions with ATLAS. Physics Letters B, 789, 167-190
Open this publication in new window or tab >>Measurement of photon-jet transverse momentum correlations in 5.02 TeV Pb + Pb and pp collisions with ATLAS
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2019 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 789, p. 167-190Article in journal (Refereed) Published
Abstract [en]

Jets created in association with a photon can be used as a calibrated probe to study energy loss in the medium created in nuclear collisions. Measurements of the transverse momentum balance between isolated photons and inclusive jets are presented using integrated luminosities of 0.49 nb(-1) of Pb + Pb collision data at root(NN)-N-s = 5.02 TeV and 25 pb(-1) of pp collision data at. root s= 5.02 TeV recorded with the ATLAS detector at the LHC. Photons with transverse momentum 63.1 < p(T)(gamma) < 200 GeV and vertical bar eta(gamma vertical bar) < 2.37 are paired with all jets in the event that have p(T)(jet) > 31.6 GeV and pseudorapidity vertical bar eta(Jet)vertical bar < 2.8. The transverse momentum balance given by the jet-to-photon p(T) ratio, x(j gamma), is measured for pairs with azimuthal opening angle Delta phi > 7 pi/8. Distributions of the per-photon jet yield as a function of x(j gamma), (1/N-gamma)(dN/dx(j gamma)), are corrected for detector effects via a two-dimensional unfolding procedure and reported at the particle level. In pp collisions, the distributions are well described by Monte Carlo event generators. In Pb + Pb collisions, the x(j gamma) distribution is modified from that observed in pp collisions with increasing centrality, consistent with the picture of parton energy loss in the hot nuclear medium. The data are compared with a suite of energy-loss models and calculations.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2019
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-244092 (URN)10.1016/j.physletb.2018.12.023 (DOI)000457165400023 ()2-s2.0-85058927090 (Scopus ID)
Note

QC 20190219

Available from: 2019-02-19 Created: 2019-02-19 Last updated: 2019-02-19Bibliographically approved
Aaboud, M., Kastanas, K. A., Jensen, B., Ohm, C., Ripellino, G., Sidebo, P. E., . . . et al., . (2019). Measurement of the nuclear modification factor for inclusive jets in Pb plus Pb collisions at root s(NN)=5.02 TeV with the ATLAS detector. Physics Letters B, 790
Open this publication in new window or tab >>Measurement of the nuclear modification factor for inclusive jets in Pb plus Pb collisions at root s(NN)=5.02 TeV with the ATLAS detector
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2019 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 790Article in journal (Refereed) Published
Abstract [en]

Measurements of the yield and nuclear modification factor, R-AA, for inclusive jet production are performed using 0.49 nb(-1) of Pb+Pb data at root s(NN) = 5.02 TeV and 25 pb(-1) of Pb+Pb data at root s = 5.02 TeV with the ATLAS detector at the LHC. Jets are reconstructed with the anti-k(t) algorithm with radius parameter R = 0.4 and are measured over the transverse momentum range of 40-1000 GeV in six rapidity intervals covering vertical bar y vertical bar < 2.8. The magnitude of R-AA increases with increasing jet transverse momentum, reaching a value of approximately 0.6 at 1 TeV in the most central collisions. The magnitude of R-AA also increases towards peripheral collisions. The value of R-AA is independent of rapidity at low jet transverse momenta, but it is observed to decrease with increasing rapidity at high transverse momenta. 

Place, publisher, year, edition, pages
Elsevier, 2019
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-247991 (URN)10.1016/j.physletb.2018.10.076 (DOI)000460118200012 ()2-s2.0-85060207264 (Scopus ID)
Note

QC 20190401

Available from: 2019-04-01 Created: 2019-04-01 Last updated: 2019-04-01Bibliographically approved
Aaboud, M., Kastanas, K. A., Jensen, B., Ohm, C., Ripellino, G., Sidebo, P. E., . . . Zwalinski, L. (2019). Measurements of W and Z boson production in pp collisions at root s=5.02 TeV with the ATLAS detector. European Physical Journal C, 79(2), Article ID 128.
Open this publication in new window or tab >>Measurements of W and Z boson production in pp collisions at root s=5.02 TeV 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 2, article id 128Article in journal (Refereed) Published
Abstract [en]

Measurements of fiducial integrated and differential cross sections for inclusive W +, W -and Z boson production are reported. They are based on 25.0 +/- 0.5 pb -1 of pp collision data at v s = 5.02 TeV collected with the ATLAS detector at the CERN Large Hadron Collider. Electron and muon decay channels are analysed, and the combined W +, W -and Z integrated cross sections are found to be sW+ = 2266 +/- 9 (stat) +/- 29 (syst) +/- 43 (lumi) pb, sW-= 1401 +/- 7 (stat) +/- 18 (syst) +/- 27 (lumi) pb, and sZ = 374.5 +/- 3.4 (stat)+/- 3.6 (syst)+/- 7.0 (lumi) pb, in good agreement with next-to-next-to-leading-order QCD crosssection calculations. Thesemeasurements serve as references for Pb+ Pb interactions at the LHC at v sNN = 5.02 TeV.

Place, publisher, year, edition, pages
SPRINGER, 2019
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-245140 (URN)10.1140/epjc/s10052-019-6622-x (DOI)000458466200001 ()
Note

QC20190313

Available from: 2019-03-13 Created: 2019-03-13 Last updated: 2019-04-04Bibliographically approved
Aaboud, M., Kastanas, K. A., Jensen, B., Ohm, C., Ripellino, G., Sidebo, P. E., . . . et al., . (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.

Place, publisher, year, edition, pages
SPRINGER, 2019
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-243947 (URN)10.1140/epjc/s10052-018-6500-y (DOI)000456628900001 ()2-s2.0-85060934269 (Scopus ID)
Note

QC 20190212

Available from: 2019-02-12 Created: 2019-02-12 Last updated: 2019-02-12Bibliographically approved
Aaboud, M., Kastanas, K. A., Lund-Jensen, B., Ohm, C., Ripellino, G., Sidebo, P. E., . . . et al., . (2019). Search for heavy Majorana or Dirac neutrinos and right-handed W gauge bosons in final states with two charged leptons and two jets at TeV with the ATLAS detector. JOURNAL OF HIGH ENERGY PHYSICS (1), Article ID 16.
Open this publication in new window or tab >>Search for heavy Majorana or Dirac neutrinos and right-handed W gauge bosons in final states with two charged leptons and two jets at TeV with the ATLAS detector
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2019 (English)In: JOURNAL OF HIGH ENERGY PHYSICS, no 1, article id 16Article in journal (Refereed) Published
Abstract [en]

A search for heavy right-handed Majorana or Dirac neutrinos N (R) and heavy right-handed gauge bosons W (R) is performed in events with a pair of energetic electrons or muons, with the same or opposite electric charge, and two energetic jets. The events are selected from pp collision data with an integrated luminosity of 36.1 fb(-1) collected by the ATLAS detector at TeV. No significant deviations from the Standard Model are observed. The results are interpreted within the theoretical framework of a left-right symmetric model and lower limits are set on masses in the heavy right-handed W boson and neutrino mass plane. The excluded region extends to TeV for both Majorana and Dirac N (R) neutrinos.

Place, publisher, year, edition, pages
SPRINGER, 2019
Keywords
Hadron-Hadron scattering (experiments)
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-244121 (URN)10.1007/JHEP01(2019)016 (DOI)000456888300001 ()2-s2.0-85060177064 (Scopus ID)
Note

QC 20190219

Available from: 2019-02-19 Created: 2019-02-19 Last updated: 2019-02-19Bibliographically approved
Aaboud, M., Kastanas, K. A., Lund-Jensen, B., Ohm, C., Ripellino, G., Sidebo, P. E., . . . et al., . (2019). Search for Higgs boson decays into a pair of light bosons in the bb mu mu final state in pp collision at root s=13 TeV with the ATLAS detector. Physics Letters B, 790
Open this publication in new window or tab >>Search for Higgs boson decays into a pair of light bosons in the bb mu mu final state in pp collision 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. 790Article in journal (Refereed) Published
Abstract [sv]

A search for decays of the Higgs boson into a pair of new spin-zero particles, H -> aa, where the a-bosons decay into a b-quark pair and a muon pair, is presented. The search uses 36.1 fb(-1) of proton-proton collision data at root s = 13 TeV recorded by the ATLAS experiment at the LHC in 2015 and 2016. No significant deviation from the Standard Model prediction is observed. Upper limits at 95% confidence level are placed on the branching ratio (sigma(H)/sigma(SM)) x B(H -> aa -> bb mu mu), ranging from 1.2 x 10(-4) to 8.4 x 10(-4) in the a-boson mass range of 20-60 GeV. Model-independent limits are set on the visible production cross-section times the branching ratio to the bb mu mu final state for new physics, sigma(vis)(X) x B(X -> bb mu mu), ranging from 0.1 fb to 0.73 fb for m(mu mu) between 18 and 62 GeV.

Place, publisher, year, edition, pages
Elsevier, 2019
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-247993 (URN)10.1016/j.physletb.2018.10.073 (DOI)000460118200001 ()2-s2.0-85059937238 (Scopus ID)
Note

QC 20190401

Available from: 2019-04-01 Created: 2019-04-01 Last updated: 2019-04-01Bibliographically approved
Aaboud, M., Kastanas, K. A., Lund-Jensen, B., Ohm, C., Ripellino, G., Sidebo, P. E., . . . et al., . (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. The Author(s).

Place, publisher, year, edition, pages
Elsevier, 2019
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-242983 (URN)10.1016/j.physletb.2018.09.062 (DOI)000455364400042 ()2-s2.0-85057390982 (Scopus ID)
Note

QC 20190212

Available from: 2019-02-12 Created: 2019-02-12 Last updated: 2019-02-12Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0001-6945-1916

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