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Sökning: WFRF:(Argyropoulos T.) > Aad G.

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1.
  • Aad, G., et al. (författare)
  • Dynamics of isolated-photon plus jet production in pp collisions at root s=7 TeV with the ATLAS detector
  • 2013
  • Ingår i: Nuclear Physics B. - Elsevier Science Bv. - 0550-3213. ; 875:3, s. 483-535
  • Tidskriftsartikel (refereegranskat)abstract
    • The dynamics of isolated-photon plus jet production in pp collisions at a centre-of-mass energy of 7 TeV has been studied with the ATLAS detector at the LHC using an integrated luminosity of 37 pb(-1). Measurements of isolated-photon plus jet bin-averaged cross sections are presented as functions of photon transverse energy, jet transverse momentum and jet rapidity. In addition, the bin-averaged cross sections as functions of the difference between the azimuthal angles of the photon and the jet, the photon jet invariant mass and the scattering angle in the photon jet centre-of-mass frame have been measured. Next-to-leading-order QCD calculations are compared to the measurements and provide a good description of the data, except for the case of the azimuthal opening angle. (C) 2013 CERN. Published by Elsevier B.V. All rights reserved.
2.
  • Aad, G., et al. (författare)
  • Measurement of Top Quark Polarization in Top-Antitop Events from Proton- Proton Collisions at root s=7 TeV Using the ATLAS Detector
  • 2013
  • Ingår i: Physical Review Letters. - Amer. Physical Soc.. - 0031-9007. ; 111:23, s. 232002
  • Tidskriftsartikel (refereegranskat)abstract
    • This Letter presents measurements of the polarization of the top quark in top-antitop quark pair events, using 4: 7 fb(-1) of proton-proton collision data recorded with the ATLAS detector at the Large Hadron Collider at root s = 7 TeV. Final states containing one or two isolated leptons ( electrons or muons) and jets are considered. Two measurements of alpha P-l, the product of the leptonic spin-analyzing power and the top quark polarization, are performed assuming that the polarization is introduced by either a CP conserving or a maximally CP violating production process. The measurements obtained, alpha P-l(CPC) = -0: 035 +/- 0: 014(stat) +/- 0: 037(syst) and alpha P-l(CPV) = 0: 020 +/- 0: 016(stat)(-0.017)(+0.013)(syst), are in good agreement with the standard model prediction of negligible top quark polarization.
3.
  • Aad, G., et al. (författare)
  • Search for charginos nearly mass degenerate with the lightest neutralino based on a disappearing-track signature in pp collisions at root(s)=8 TeV with the ATLAS detector
  • 2013
  • Ingår i: Physical Review D. - Amer. Physical Soc.. - 1550-7998. ; 88:11, s. 112006
  • Tidskriftsartikel (refereegranskat)abstract
    • A search is presented for direct chargino production based on a disappearing-track signature using 20.3 fb(-1) of proton-proton collisions at root s = 8 TeV collected with the ATLAS experiment at the LHC. In anomaly-mediated supersymmetry breaking (AMSB) models, the lightest chargino is nearly mass degenerate with the lightest neutralino and its lifetime is long enough to be detected in the tracking detectors by identifying decays that result in tracks with no associated hits in the outer region of the tracking system. Some models with supersymmetry also predict charginos with a significant lifetime. This analysis attains sensitivity for charginos with a lifetime between 0.1 and 10 ns, and significantly surpasses the reach of the LEP experiments. No significant excess above the background expectation is observed for candidate tracks with large transverse momentum, and constraints on chargino properties are obtained. In the AMSB scenarios, a chargino mass below 270 GeV is excluded at 95% confidence level.
4.
  • Aad, G., et al. (författare)
  • Measurement of angular correlations in Drell-Yan lepton pairs to probe Z/gamma* boson transverse momentum at root s=7 TeV with the ATLAS detector
  • 2013
  • Ingår i: Physics Letters B. - Elsevier. - 0370-2693. ; 720:1-3, s. 32-51
  • Tidskriftsartikel (refereegranskat)abstract
    • A measurement of angular correlations in Drell-Yan lepton pairs via the phi(eta)* observable is presented. This variable probes the same physics as the Z/gamma* boson transverse momentum with a better experimental resolution. The Z/gamma* -> e(+)e(-) and Z/gamma* -> mu(+)mu(-) decays produced in proton-proton collisions at a centre-of-mass energy of root s = 7 TeV are used. The data were collected with the ATLAS detector at the LHC and correspond to an integrated luminosity of 4.6 fb(-1). Normalised differential cross sections as a function of phi(eta)* are measured separately for electron and muon decay channels. These channels are then combined for improved accuracy. The cross section is also measured double differentially as a function of phi(eta)* for three independent bins of the Z boson rapidity. The results are compared to QCD calculations and to predictions from different Monte Carlo event generators. The data are reasonably well described, in all measured Z boson rapidity regions, by resummed QCD predictions combined with fixed-order perturbative QCD calculations or by some Monte Carlo event generators. The measurement precision is typically better by one order of magnitude than present theoretical uncertainties. (C) 2013 CERN. Published by Elsevier B.V. All rights reserved.
5.
  • Aad, G., et al. (författare)
  • Measurement of jet shapes in top-quark pair events at root s=7 TeV using the ATLAS detector
  • 2013
  • Ingår i: European Physical Journal C. - Springer. - 1434-6044. ; 73:12
  • Tidskriftsartikel (refereegranskat)abstract
    • A measurement of jet shapes in top-quark pair events using 1.8 fb(-1) of pp collision data recorded by the ATLAS detector at the LHC is presented. Samples of top-quark pair events are selected in both the single-lepton and dilepton final states. The differential and integrated shapes of the jets initiated by bottom-quarks from the top-quark decays are compared with those of the jets originated by light-quarks from the hadronic W-boson decays in the single-lepton channel. The light-quark jets are found to have a narrower distribution of the momentum flow inside the jet area than b-quark jets.
6.
  • Aad, G., et al. (författare)
  • Measurement of k(T) splitting scales in W -> l nu events at root s=7 TeV with the ATLAS detector
  • 2013
  • Ingår i: European Physical Journal C. - Springer. - 1434-6044. ; 73:5, s. 2432
  • Tidskriftsartikel (refereegranskat)abstract
    • A measurement of splitting scales, as defined by the kT clustering algorithm, is presented for final states containing a W boson produced in proton-proton collisions at a centre-of-mass energy of 7 TeV. The measurement is based on the full 2010 data sample corresponding to an integrated luminosity of 36 pb(-1) which was collected using the ATLAS detector at the CERN Large Hadron Collider. Cluster splitting scales are measured in events containing W bosons decaying to electrons or muons. The measurement comprises the four hardest splitting scales in a k(T) cluster sequence of the hadronic activity accompanying the W boson, and ratios of these splitting scales. Backgrounds such as multi-jet and top-quark-pair production are subtracted and the results are corrected for detector effects. Predictions from various Monte Carlo event generators at particle level are compared to the data. Overall, reasonable agreement is found with all generators, but larger deviations between the predictions and the data are evident in the soft regions of the splitting scales.
7.
  • Aad, G., et al. (författare)
  • Observation of Associated Near-Side and Away-Side Long-Range Correlations in root S-NN=5.02 TeV Proton-Lead Collisions with the ATLAS Detector
  • 2013
  • Ingår i: Physical Review Letters. - American Physical Society. - 0031-9007. ; 110:18, s. 182302
  • Tidskriftsartikel (refereegranskat)abstract
    • Two-particle correlations in relative azimuthal angle (Delta phi) and pseudorapidity (Delta eta) are measured in root S-NN = 5.02 TeV p + Pb collisions using the ATLAS detector at the LHC. The measurements are performed using approximately 1 mu b(-1) of data as a function of transverse momentum (p(T)) and the transverse energy (Sigma E-T(Pb)) summed over 3.1 < eta < 4.9 in the direction of the Pb beam. The correlation function, constructed from charged particles, exhibits a long-range (2 < vertical bar Delta eta vertical bar < 5) "near-side" (Delta phi similar to 0) correlation that grows rapidly with increasing Sigma E-T(Pb). A long-range "away-side" (Delta phi similar to pi) correlation, obtained by subtracting the expected contributions from recoiling dijets and other sources estimated using events with small Sigma E-T(Pb), is found to match the near-side correlation in magnitude, shape (in Delta eta and Delta phi) and Sigma E-T(Pb) dependence. The resultant Delta phi correlation is approximately symmetric about pi/2, and is consistent with a dominant cos2 Delta phi modulation for all Sigma E-T(Pb) ranges and particle p(T).
8.
  • Aad, G., et al. (författare)
  • Search for long-lived stopped R-hadrons decaying out of time with pp collisions using the ATLAS detector
  • 2013
  • Ingår i: Physical Review D. - Amer. Physical Soc.. - 1550-7998. ; 88:11, s. 112003
  • Tidskriftsartikel (refereegranskat)abstract
    • An updated search is performed for gluino, top squark, or bottom squark R-hadrons that have come to rest within the ATLAS calorimeter, and decay at some later time to hadronic jets and a neutralino, using 5.0 and 22.9 fb(-1) of pp collisions at 7 and 8 TeV, respectively. Candidate decay events are triggered in selected empty bunch crossings of the LHC in order to remove pp collision backgrounds. Selections based on jet shape and muon system activity are applied to discriminate signal events from cosmic ray and beam-halo muon backgrounds. In the absence of an excess of events, improved limits are set on gluino, stop, and sbottom masses for different decays, lifetimes, and neutralino masses. With a neutralino of mass 100 GeV, the analysis excludes gluinos with mass below 832 GeV (with an expected lower limit of 731 GeV), for a gluino lifetime between 10 mu s and 1000 s in the generic R-hadron model with equal branching ratios for decays to q (q) over bar(chi) over tilde (0) and g (chi) over tilde (0). Under the same assumptions for the neutralino mass and squark lifetime, top squarks and bottom squarks in the Regge R-hadron model are excluded with masses below 379 and 344 GeV, respectively.
9.
  • Aad, G., et al. (författare)
  • Search for microscopic black holes in a like-sign dimuon final state using large track multiplicity with the ATLAS detector
  • 2013
  • Ingår i: Physical Review D. - Amer. Physical Soc.. - 1550-7998. ; 88:7, s. 072001
  • Tidskriftsartikel (refereegranskat)abstract
    • A search is presented for microscopic black holes in a like-sign dimuon final state in proton-proton collisions at root s = 8 TeV. The data were collected with the ATLAS detector at the Large Hadron Collider in 2012 and correspond to an integrated luminosity of 20.3 fb(-1). Using a high track multiplicity requirement, 0.6 +/- 0.2 background events from Standard Model processes are predicted and none observed. This result is interpreted in the context of low-scale gravity models and 95% C.L. lower limits on microscopic black hole masses are set for different model assumptions.
10.
  • Aad, G., et al. (författare)
  • Search for nonpointing photons in the diphoton and E-T(miss) final state in root s=7 TeV proton-proton collisions using the ATLAS detector
  • 2013
  • Ingår i: Physical Review D. - American Physical Society. - 1550-7998. ; 88:1, s. 012001
  • Tidskriftsartikel (refereegranskat)abstract
    • A search has been performed for photons originating in the decay of a neutral long-lived particle, exploiting the capabilities of the ATLAS electromagnetic calorimeter to make precise measurements of the flight direction of photons, as well as the calorimeter's excellent time resolution. The search has been made in the diphoton plus missing transverse energy final state, using the full data sample of 4.8 fb(-1) of 7 TeV proton-proton collisions collected in 2011 with the ATLAS detector at the LHC. No excess is observed above the background expected from Standard Model processes. The results are used to set exclusion limits in the context of gauge mediated supersymmetry breaking models, with the lightest neutralino being the next-to-lightest supersymmetric particle and decaying with a lifetime in excess of 0.25 ns into a photon and a gravitino.
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  • Resultat 1-10 av 68
  • [1]234567Nästa
 
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