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Coniavitis, Elias
Publications (10 of 128) Show all publications
Aad, G., Bergeås, E. K., Brenner, R., Buszello, C. P., Coniavitis, E., Ekelöf, T., . . . Zwalinski, L. (2016). Measurement of the centrality dependence of the charged-particle pseudorapidity distribution in proton-lead collisions at root s(NN)=5.02 TeV with the ATLAS detector. European Physical Journal C, 76(4), Article ID 199.
Open this publication in new window or tab >>Measurement of the centrality dependence of the charged-particle pseudorapidity distribution in proton-lead collisions at root s(NN)=5.02 TeV with the ATLAS detector
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2016 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 76, no 4, article id 199Article in journal (Refereed) Published
Abstract [en]

The centrality dependence of the mean charged-particle multiplicity as a function of pseudorapidity is measured in approximately 1 mu b(-1) of proton-lead collisions at a nucleon-nucleon centre-of-mass energy of root s(NN) = 5.02 TeV using the ATLAS detector at the Large Hadron Collider. Charged particles with absolute pseudorapidity less than 2.7 are reconstructed using the ATLAS pixel detector. The p + Pb collision centrality is characterised by the total transverse energy measured in the Pb-going direction of the forward calorimeter. The charged-particle pseudorapidity distributions are found to vary strongly with centrality, with an increasing asymmetry between the proton-going and Pb-going directions as the collisions become more central. Three different estimations of the number of nucleons participating in the p + Pb collision have been carried out using the Glauber model as well as two Glauber-Gribov inspired extensions to the Glauber model. Charged-particle multiplicities per participant pair are found to vary differently for these three models, highlighting the importance of including colour fluctuations in nucleon-nucleon collisions in the modelling of the initial state of p + Pb collisions.

National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-297527 (URN)10.1140/epjc/s10052-016-4002-3 (DOI)000375306400002 ()
Note

ATLAS Collaboration, for complete list of authors see http://dx.doi.org/10.1140/epjc/s10052-016-4002-3

Funding: We honour the memory of our colleague Alexey Antonov, who was closely involved in the work described here, and died shortly after its completion. We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of ANPCyT, Argentina; YerPhI, Armenia; ARC, Australia; BMWFW and FWF, Austria; ANAS, Azerbaijan; SSTC, Belarus; CNPq and FAPESP, Brazil; NSERC, NRC and CFI, Canada; CERN; CONICYT, Chile; CAS, MOST and NSFC, China; COLCIENCIAS, Colombia; MSMTCR, MPOCR and VSC CR, Czech Republic; DNRF, DNSRC and Lundbeck Foundation, Denmark; IN2P3-CNRS, CEA-DSM/IRFU, France; GNSF, Georgia; BMBF, HGF, and MPG, Germany; GSRT, Greece; RGC, Hong Kong SAR, China; ISF, I-CORE and Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; FOM and NWO, Netherlands; RCN, Norway; MNiSW and NCN, Poland; FCT, Portugal; MNE/IFA, Romania; MES of Russia and NRC KI, Russian Federation; JINR; MESTD, Serbia; MSSR, Slovakia; ARRS and MIZS, Slovenia; DST/NRF, South Africa; MINECO, Spain; SRC and Wallenberg Foundation, Sweden; SERI, SNSF and Cantons of Bern and Geneva, Switzerland; MOST, Taiwan; TAEK, Turkey; STFC, UK; DOE and NSF, USA. In addition, individual groups and members have received support from BCKDF, the Canada Council, CANARIE, CRC, Compute Canada, FQRNT, and the Ontario Innovation Trust, Canada; EPLANET, ERC, FP7, Horizon 2020 and Marie Sklodowska-Curie Actions, European Union; Investissements d'Avenir Labex and Idex, ANR, Region Auvergne and Fondation Partager le Savoir, France; DFG and AvH Foundation, Germany; Herakleitos, Thales and Aristeia programmes co-financed by EU-ESF and the Greek NSRF; BSF, GIF and Minerva, Israel; BRF, Norway; the Royal Society and Leverhulme Trust, UK. The crucial computing support from all WLCG partners is acknowledged gratefully, in particular from CERN and the ATLAS Tier-1 facilities at TRIUMF (Canada), NDGF (Denmark, Norway, Sweden), CC-IN2P3 (France), KIT/GridKA (Germany), INFN-CNAF (Italy), NL-T1 (Netherlands), PIC (Spain), ASGC (Taiwan), RAL (UK) and BNL (USA) and in the Tier-2 facilities worldwide.

Available from: 2016-06-23 Created: 2016-06-23 Last updated: 2017-11-28Bibliographically approved
Aad, G., Brenner, R., Buszello, C. P., Coniavitis, E., Ekelöf, T., Ellert, M., . . . Zwalinski, L. (2015). Jet energy measurement and its systematic uncertainty in proton-proton collisions at root s=7 TeV with the ATLAS detector. European Physical Journal C, 75(1), Article ID 17.
Open this publication in new window or tab >>Jet energy measurement and its systematic uncertainty in proton-proton collisions at root s=7 TeV with the ATLAS detector
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2015 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 75, no 1, article id 17Article in journal (Refereed) Published
Abstract [en]

The jet energy scale (JES) and its systematic uncertainty are determined for jetsmeasured with the ATLAS detector using proton-proton collision data with a centre-of-mass energy of root s = 7 TeV corresponding to an integrated luminosity of 4.7 fb(-1). Jets are reconstructed from energy deposits forming topological clusters of calorimeter cells using the anti-kt algorithmwith distance parameters R = 0.4 or R = 0.6, and are calibrated using MC simulations. A residual JES correction is applied to account for differences between data and MC simulations. This correction and its systematic uncertainty are estimated using a combination of in situ techniques exploiting the transverse momentum balance between a jet and a reference object such as a photon or a Z boson, for 20 <= p(T)(jet) < 1000 GeV and pseudorapidities vertical bar eta vertical bar < 4.5. The effect of multiple proton-proton interactions is corrected for, and an uncertainty is evaluated using in situ techniques. The smallest JES uncertainty of less than 1% is found in the central calorimeter region (vertical bar eta vertical bar| < 1.2) for jets with 55 = p(T)(jet) < 500 GeV. For central jets at lower p(T), the uncertainty is about 3%. A consistent JES estimate is found using measurements of the calorimeter response of single hadrons in proton-proton collisions and test-beam data, which also provide the estimate for p(T)(jet) > 1 TeV. The calibration of forward jets is derived from dijet p(T) balance measurements. The resulting uncertainty reaches its largest value of 6% for low-p(T) jets at vertical bar eta vertical bar| = 4.5. Additional JES uncertainties due to specific event topologies, such as close-by jets or selections of event samples with an enhanced content of jets originating from light quarks or gluons, are also discussed. The magnitude of these uncertainties depends on the event sample used in a given physics analysis, but typically amounts to 0.5-3%.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-247735 (URN)10.1140/epjc/s10052-014-3190-y (DOI)000348991900001 ()
Note

ATLAS Collaboration, for complete list of authors see http://dx.doi.org/10.1140/epjc/s10052-014-3190-y.

Available from: 2015-03-23 Created: 2015-03-23 Last updated: 2018-05-18Bibliographically approved
Aad, G., Brenner, R., Buszello, C. P., Coniavitis, E., Ekelöf, T., Ellert, M., . . . Zwalinski, L. (2015). Performance of the ATLAS muon trigger in pp collisions at root s=8 TeV. European Physical Journal C, 75(3), Article ID 120.
Open this publication in new window or tab >>Performance of the ATLAS muon trigger in pp collisions at root s=8 TeV
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2015 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 75, no 3, article id 120Article in journal (Refereed) Published
Abstract [en]

The performance of the ATLAS muon trigger system is evaluated with proton-proton collision data collected in 2012 at the Large Hadron Collider at a centre-of-mass energy of 8TeV. It is primarily evaluated using events containing a pair of muons from the decay of Z bosons. The efficiency of the single-muon trigger is measured for muons with transverse momentum 25 < pT < 100 GeV, with a statistical uncertainty of less than 0.01% and a systematic uncertainty of 0.6%. The pT range for efficiency determination is extended by using muons from decays of J/Psi mesons, W bosons, and top quarks. The muon trigger shows highly uniform and stable performance. The performance is compared to the prediction of a detailed simulation.

National Category
Accelerator Physics and Instrumentation
Identifiers
urn:nbn:se:uu:diva-258124 (URN)10.1140/epjc/s10052-015-3325-9 (DOI)000355666500002 ()
Note

ATLAS Collaboration, for complete list of authors see http://dx.doi.org/10.1140/epjc/s10052-015-3325-9

Available from: 2015-07-10 Created: 2015-07-10 Last updated: 2017-12-04Bibliographically approved
Aad, G., Brenner, R., Buszello, C. P., Coniavitis, E., Ekelöf, T., Ellert, M., . . . Zwalinski, L. (2014). Comprehensive measurements of t-channel single top-quark production cross sections at root S=7 TeV with the ATLAS detector. Physical Review D. Particles and fields, 90(11), 112006
Open this publication in new window or tab >>Comprehensive measurements of t-channel single top-quark production cross sections at root S=7 TeV with the ATLAS detector
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2014 (English)In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 90, no 11, p. 112006-Article in journal (Refereed) Published
Abstract [en]

This article presents measurements of the t-channel single top-quark ((t) over bart) and top-antiquark (_ t) total production cross sections sdtq_ and sd _ tq_, their ratio Rt sdtq_= sd _ tq_, and a measurement of the inclusive production cross section sdtq _ _ tq_ in proton-proton collisions at ffiffiffi ps = 7 TeV at the LHC. Differential cross sections for the tq and _ tq processes are measured as a function of the transverse momentum and the absolute value of the rapidity of t and _ t, respectively. The analyzed data set was recorded with the ATLAS detector and corresponds to an integrated luminosity of 4.59 fb-1. Selected events contain one charged lepton, large missing transverse momentum, and two or three jets. The cross sections are measured by performing a binned maximum-likelihood fit to the output distributions of neural networks. The resulting measurements are sdtq_ 46 = 1dstat_ = 6dsyst_ pb, sd _ tq_ = 23 +/- 1dstat_ = 3dsyst_ pb, Rt = 2.04 0.13dstat_ +/-=0.12dsyst_, and sdtq _ _ tq_ = 68 +/-= 2dstat_ = 8dsyst_ pb, consistent with the Standard Model expectation. The uncertainty on the measured cross sections is dominated by systematic uncertainties, while the uncertainty on Rt is mainly statistical. Using the ratio of sdtq _ _ tq_ to its theoretical prediction, and assuming that the top-quark-related CKM matrix elements obey the relation jVtbj = jVtsj; jVtdj, we determine jVtbj = 1.02 = 0.07.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-242545 (URN)10.1103/PhysRevD.90.112006 (DOI)000346377100003 ()
Note

ATLAS Collaboration, for complete list of authors see dx.doi.org/10.1103/PhysRevD.90.112006

Available from: 2015-01-27 Created: 2015-01-27 Last updated: 2018-05-18Bibliographically approved
Aad, G., Brenner, R., Buszello, C., Coniavitis, E., Ekelöf, T., Ellert, M., . . . Zwalinski, L. (2014). Electron reconstruction and identification efficiency measurements with the ATLAS detector using the 2011 LHC proton-proton collision data. European Physical Journal C, 74(7), UNSP 2941
Open this publication in new window or tab >>Electron reconstruction and identification efficiency measurements with the ATLAS detector using the 2011 LHC proton-proton collision data
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2014 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 74, no 7, p. UNSP 2941-Article in journal (Refereed) Published
Abstract [en]

 Many of the interesting physics processes to be measured at the LHC have a signature involving one or more isolated electrons. The electron reconstruction and identification efficiencies of the ATLAS detector at the LHC have been evaluated using proton-proton collision data collected in 2011 at TeV and corresponding to an integrated luminosity of 4.7 fb. Tag-and-probe methods using events with leptonic decays of and bosons and mesons are employed to benchmark these performance parameters. The combination of all measurements results in identification efficiencies determined with an accuracy at the few per mil level for electron transverse energy greater than 30 GeV.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-231376 (URN)10.1140/epjc/s10052-014-2941-0 (DOI)000339864800001 ()
Note

ATLAS Collaboration, for complete list of authors see http://dx.doi.org/10.1140/epjc/s10052-014-2941-0

Available from: 2014-09-08 Created: 2014-09-08 Last updated: 2017-12-05Bibliographically approved
Aad, G., Brenner, R., Buszello, C. P., Coniavitis, E., Ekelöf, T., Ellert, M., . . . Zwalinski, L. (2014). Evidence for Electroweak Production of W(+/-)W(+/-)jj in pp Collisions at root s=8 TeV with the ATLAS Detector. Physical Review Letters, 113(14), 141803
Open this publication in new window or tab >>Evidence for Electroweak Production of W(+/-)W(+/-)jj in pp Collisions at root s=8 TeV with the ATLAS Detector
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2014 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 113, no 14, p. 141803-Article in journal (Refereed) Published
Abstract [en]

This Letter presents the first study of WWjj, same-electric-charge diboson production in associationwith two jets, using 20.3 fb−1 of proton-proton collision data at ffiffiffis p ¼ 8 TeV recorded by the ATLASdetector at the Large Hadron Collider. Events with two reconstructed same-charge leptons (ee, eμ,and μμ) and two or more jets are analyzed. Production cross sections are measured in two fiducialregions, with different sensitivities to the electroweak and strong production mechanisms. First evidencefor WWjj production and electroweak-only WWjj production is observed with a significance of 4.5and 3.6 standard deviations, respectively. The measured production cross sections are in agreement withstandard model predictions. Limits at 95% confidence level are set on anomalous quartic gauge couplings.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-238778 (URN)10.1103/PhysRevLett.113.141803 (DOI)000344031200004 ()25325632 (PubMedID)
Note

ATLAS Collaboration, for complete list of authors see http://dx.doi.org/10.1103/PhysRevLett.113.141803

Available from: 2014-12-16 Created: 2014-12-16 Last updated: 2017-12-05Bibliographically approved
Aad, G., Brenner, R., Buszello, C. P., Coniavitis, E., Ekelöf, T., Ellert, M., . . . Zwalinski, L. (2014). Flavor tagged time-dependent angular analysis of the B-s(0) -> J/psi phi decay and extraction of Delta Gamma(s) and the weak phase phi(s) in ATLAS. Physical Review D, 90(5), 052007
Open this publication in new window or tab >>Flavor tagged time-dependent angular analysis of the B-s(0) -> J/psi phi decay and extraction of Delta Gamma(s) and the weak phase phi(s) in ATLAS
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2014 (English)In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 90, no 5, p. 052007-Article in journal (Refereed) Published
Abstract [en]

This paper presents a search for new particles in events with one lepton (electron or muon) and missing transverse momentum using 20.3 fb(-1) of proton-proton collision data at root s = 8 TeV recorded by the ATLAS experiment at the Large Hadron Collider. No significant excess beyond Standard Model expectations is observed. A W' with Sequential Standard Model couplings is excluded at the 95% confidence level for masses up to 3.24 TeV. Excited chiral bosons (W*) with equivalent coupling strengths are excluded for masses up to 3.21 TeV. In the framework of an effective field theory limits are also set on the dark matter-nucleon scattering cross-section as well as the mass scale M-* of the unknown mediating interaction for dark matter pair production in association with a leptonically decaying W.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-235570 (URN)10.1103/PhysRevD.90.052007 (DOI)000342147500002 ()
Note

ATLAS Collaboration, for complete list of authors see http://dx.doi.org/10.1103/PhysRevD.90.052007

Available from: 2014-11-06 Created: 2014-11-06 Last updated: 2018-05-18Bibliographically approved
Aad, G., Brenner, R., Buszello, C. P., Coniavitis, E., Ekelöf, T., Ellert, M., . . . Zwalinski, L. (2014). Light-quark and gluon jet discrimination in collisions at root s=7 TeV with the ATLAS detector. European Physical Journal C, 74(8), UNSP 3023
Open this publication in new window or tab >>Light-quark and gluon jet discrimination in collisions at root s=7 TeV with the ATLAS detector
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2014 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 74, no 8, p. UNSP 3023-Article in journal (Refereed) Published
Abstract [en]

A likelihood-based discriminant for the identification of quark- and gluon-initiated jets is built and validated using 4.7 fb −1 of proton–proton collision data at s√=7    TeV collected with the ATLAS detector at the LHC. Data samples with enriched quark or gluon content are used in the construction and validation of templates of jet properties that are the input to the likelihood-based discriminant. The discriminating power of the jet tagger is established in both data and Monte Carlo samples within a systematic uncertainty of ≈ 10–20 %. In data, light-quark jets can be tagged with an efficiency of ≈50% while achieving a gluon-jet mis-tag rate of ≈25% in a pT range between 40 GeV and 360 GeV for jets in the acceptance of the tracker. The rejection of gluon-jets found in the data is significantly below what is attainable using a Pythia 6 Monte Carlo simulation, where gluon-jet mis-tag rates of 10 % can be reached for a 50 % selection efficiency of light-quark jets using the same jet properties.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-233697 (URN)10.1140/epjc/s10052-014-3023-z (DOI)000340948500001 ()
Note

ATLAS Collaboration, for complete list of authors see http://dx.doi.org/10.1140/epjc/s10052-014-3023-z

Available from: 2014-10-08 Created: 2014-10-08 Last updated: 2017-12-05Bibliographically approved
Aad, G., Brenner, R., Buszello, C. P., Coniavitis, E., Ekelöf, T., Ellert, M., . . . Zwalinski, L. (2014). Measurement of chi(c1) and chi(c2) production with root s=7 TeV pp collisions at ATLAS. Journal of High Energy Physics (JHEP) (7), 154
Open this publication in new window or tab >>Measurement of chi(c1) and chi(c2) production with root s=7 TeV pp collisions at ATLAS
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2014 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 7, p. 154-Article in journal (Refereed) Published
Abstract [en]

The prompt and non-prompt production cross-sections for the χ c1 and χ c2 charmonium states are measured in pp collisions at TeX = 7 TeV with the ATLAS detector at the LHC using 4.5 fb−1 of integrated luminosity. The χ c states are reconstructed through the radiative decay χ c J/ψγ (with J/ψμ + μ ) where photons are reconstructed from γe + e conversions. The production rate of the χ c2 state relative to the χ c1 state is measured for prompt and non-prompt χ c as a function of J/ψ transverse momentum. The prompt χ c cross-sections are combined with existing measurements of prompt J/ψ production to derive the fraction of prompt J/ψ produced in feed-down from χ c decays. The fractions of χ c1 and χ c2 produced in b-hadron decays are also measured.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-232771 (URN)10.1007/JHEP07(2014)154 (DOI)000340391300001 ()
Note

ATLAS Collaboration, for complete list of authors see http://dx.doi.org/10.1007/JHEP07(2014)154

Available from: 2014-09-24 Created: 2014-09-24 Last updated: 2018-05-18Bibliographically approved
Aad, G., Brenner, R., Buszello, C. P., Coniavitis, E., Ekelöf, T., Ellert, M., . . . Zwalinski, L. (2014). Measurement of dijet cross-sections in pp collisions at 7 TeV centre-of-mass energy using the ATLAS detector. Journal of High Energy Physics (JHEP) (5), 059
Open this publication in new window or tab >>Measurement of dijet cross-sections in pp collisions at 7 TeV centre-of-mass energy using the ATLAS detector
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2014 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 5, p. 059-Article in journal (Refereed) Published
Abstract [en]

Double-differential dijet cross-sections measured in pp collisions at the LHC with a 7 TeV centre-of-mass energy are presented as functions of dijet mass and half the rapidity separation of the two highest-p(T) jets. These measurements are obtained using data corresponding to an integrated luminosity of 4.5 fb(-1), recorded by the ATLAS detector in 2011. The data are corrected for detector effects so that cross-sections are presented at the particle level. Cross-sections are measured up to 5 TeV dijet mass using jets reconstructed with the anti-k(t) algorithm for values of the jet radius parameter of 0.4 and 0.6. The cross-sections are compared with next-to-leading-order perturbative QCD calculations by NLOJet++ corrected to account for non-perturbative effects. Comparisons with POWHEG predictions, using a next-to-leading-order matrix element calculation interfaced to a parton-shower Monte Carlo simulation, are also shown. Electroweak effects are accounted for in both cases. The quantitative comparison of data and theoretical predictions obtained using various parameterizations of the parton distribution functions is performed using a frequentist method. In general, good agreement with data is observed for the NLOJet++ theoretical predictions when using the CT10, NNPDF2.1 and MSTW 2008 PDF sets. Disagreement is observed when using the ABM11 and HERAPDF1.5 PDF sets for some ranges of dijet mass and half the rapidity separation. An example setting a lower limit on the compositeness scale for a model of contact interactions is presented, showing that the unfolded results can be used to constrain contributions to dijet production beyond that predicted by the Standard Model.

Keywords
Jets, Jet physics, Hadron-Hadron Scattering
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-228586 (URN)10.1007/JHEP05(2014)059 (DOI)000336740400001 ()
Note

ATLAS Collaboration, for complete list of authors see http://dx.doi.org/10.1007/JHEP05(2014)059

Available from: 2014-07-17 Created: 2014-07-17 Last updated: 2017-12-05Bibliographically approved
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