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  • 301. Aaboud, M.
    et al.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Sidebo, P. Edvin
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L.
    et al.,
    Search for top squarks in final states with one isolated lepton, jets, and missing transverse momentum in root s=13 TeV pp collisions with the ATLAS detector2016Inngår i: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 94, nr 5, artikkel-id 052009Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The results of a search for the top squark, the supersymmetric partner of the top quark, in final states with one isolated electron or muon, jets, and missing transverse momentum are reported. The search uses the 2015 LHC pp collision data at a center-of-mass energy of root s = 13 TeV recorded by the ATLAS detector and corresponding to an integrated luminosity of 3.2 fb(-1). The analysis targets two types of signal models: gluino-mediated pair production of top squarks with a nearly mass-degenerate top squark and neutralino and direct pair production of top squarks, decaying to the top quark and the lightest neutralino. The experimental signature in both signal scenarios is similar to that of a top quark pair produced in association with large missing transverse momentum. No significant excess over the Standard Model background prediction is observed, and exclusion limits on gluino and top squark masses are set at 95% confidence level. The results extend the LHC run-1 exclusion limit on the gluino mass up to 1460 GeV in the gluino-mediated scenario in the high gluino and low top squark mass region and add an excluded top squark mass region from 745 to 780 GeV for the direct top squark model with a massless lightest neutralino. The results are also reinterpreted to set exclusion limits in a model of vectorlike top quarks.

  • 302. Aaboud, M
    et al.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Sidebo, P. Edvin
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L
    et al.,
    Search for triboson (WWW -/+)-W-+/--W-+/- production in pp collisions at root s=8 TeV with the ATLAS detector2017Inngår i: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 77, nr 3, artikkel-id 141Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper reports a search for triboson (WWW -/+)-W-+/--W-+/- production in two decay channels ((WWW -/+)-W-+/--W-+/- -> l(+/-)vl(+/-)vl(-/+) v and (WWW -/+)-W-+/--W-+/- -> l(+/-)vl(+/-)vjj with l = e, mu) in proton-proton collision data corresponding to an integrated luminosity of 20.3 fb(-1) at a centre-of-mass energy of 8 TeV with the ATLAS detector at the Large Hadron Collider. Events with exactly three charged leptons, or two leptons with the same electric charge in association with two jets, are selected. The total number of events observed in data is consistent with the Standard Model (SM) predictions. The observed 95% confidence level upper limit on the (WWW -/+)-W-+/--W-+/- production cross section is found to be 730 fb with an expected limit of 560 fb in the absence of SM (WWW -/+)-W-+/--W-+/- production. Limits are also set on WWWW anomalous quartic gauge couplings.

  • 303. Aaboud, M
    et al.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Sidebo, P. Edvin
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L
    et al.,
    Searches for heavy diboson resonances in pp collisions at root S=13 TeV with the ATLAS detector2016Inngår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, nr 9, artikkel-id 173Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Searches for new heavy resonances decaying to WW, WZ, and ZZ bosons are presented, using a data sample corresponding to 3.2 fb(-1) of pp collisions at root S = 13 TeV collected with the ATLAS detector at the CERN Large Hadron Collider. Analyses selecting vvqq, lvqq, llqq and qqqq final states are combined, searching for a narrow-width resonance with mass between 500 and 3000 GeV. The discriminating variable is either an invariant mass or a transverse mass. No significant deviations from the Standard Model predictions are observed. Three benchmark models are tested: a model predicting the existence of a new heavy scalar singlet, a simplified model predicting a heavy vector-boson triplet, and a bulk Randall-Sundrum model with a heavy spin-2 graviton. Cross-section limits are set at the 95% confidence level and are compared to theoretical cross-section predictions for a variety of models. The data exclude a scalar singlet with mass below 2650 GeV, a heavy vector-boson triplet with mass below 2600 GeV, and a graviton with mass below 1100 GeV. These results significantly extend the previous limits set using pp collisions at root S = 8 TeV.

  • 304. Aaboud, M.
    et al.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Sidebo, P. Edvin
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L.
    et al.,
    Search for minimal supersymmetric standard model Higgs Bosons H / A and for a Z boson in the ττ final stateproduced in pp collisions at √s=13 TeV with the ATLAS detector2016Inngår i: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 76, nr 11Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A search for neutral Higgs bosons of the minimal supersymmetric standard model (MSSM) and for a heavneutral Z boson is performed using a data sample corresponding to an integrated luminosity of 3.2 fb- 1 from proton–proton collisions at s=13 TeV recorded by the ATLAS detector at the LHC. The heavy resonance is assumed to decay to a τ+τ- pair with at least one τ lepton decaying to final states with hadrons and a neutrino. The search is performed in the mass range of 0.2–1.2 TeV for the MSSM neutral Higgs bosons and 0.5–2.5 TeV for the heavy neutral Z boson. The data are in good agreement with the background predicted by the Standard Model. The results are interpreted in MSSM and Z benchmark scenarios. The most stringent constraints on the MSSM mA–tan β space exclude at 95 % confidence level (CL) tan β> 7.6 for mA= 200 GeV in the mhmod+ MSSM scenario. For the Sequential Standard Model, a ZSSM′ mass up to 1.90 TeV is excluded at 95 % CL and masses up to 1.82–2.17 TeV are excluded for a ZSFM′ of the strong flavour model.

  • 305. Aaboud, M.
    et al.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Sidebo, P. Edvin
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L.
    et. al.,
    Search for resonances in the mass distribution of jet pairs with one or two jets identified as b-jets in proton–proton collisions at s=13 TeV with the ATLAS detector2016Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 759, s. 229-246Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Searches for high-mass resonances in the dijet invariant mass spectrum with one or two jets identified as b  -jets are performed using an integrated luminosity of 3.2 fb−1 of proton–proton collisions with a centre-of-mass energy of  recorded by the ATLAS detector at the Large Hadron Collider. No evidence of anomalous phenomena is observed in the data, which are used to exclude, at 95% credibility level, excited bquarks with masses from 1.1 TeV to 2.1 TeV and leptophobic Z bosons with masses from 1.1 TeV to 1.5 TeV. Contributions of a Gaussian signal shape with effective cross sections ranging from approximately 0.4 to 0.001 pb are also excluded in the mass range 1.5–5.0 TeV.

  • 306. Aaboud, M.
    et al.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Sidebo, P. Edvin
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L.
    et al.,
    Study of the rare decays of Bs0 and B0 into muon pairs from data collected during the LHC Run 1 with the ATLAS detector2016Inngår i: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 76, nr 9, artikkel-id 513Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A search is performed for a heavy particle decaying into different flavour dilepton pairs (, or ), using 3.2 fb of proton-proton collision data at TeV collected in 2015 by the ATLAS detector at the Large Hadron Collider. No excess over the Standard Model prediction is observed. Limits at the 95 % credibility level are set on the mass of a boson with lepton-flavour-violating couplings at 3.0, 2.7 and 2.6 TeV, and on the mass of a supersymmetric sneutrino with R-parity-violating couplings at 2.3, 2.2 and 1.9 TeV, for , and final states, respectively. The results are also interpreted as limits on the threshold mass for quantum black hole production.

  • 307. Aaboud, M.
    et al.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Sidebo, P. Edvin
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L.
    et.al.,
    Search for the Higgs boson produced in association with a W boson and decaying to four b-quarks via two spin-zero particles in pp collisions at 13 TeV with the ATLAS detector2016Inngår i: The European Physical Journal C, ISSN 1434-6044, Vol. 76, nr 11Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents a dedicated search for exotic decays of the Higgs boson to a pair of new spin-zero particles, H→ aa, where the particle a decays to b-quarks and has a mass in the range of 20–60 GeV. The search is performed in events where the Higgs boson is produced in association with a W boson, giving rise to a signature of a lepton (electron or muon), missing transverse momentum, and multiple jets from b-quark decays. The analysis is based on the full dataset of pp collisions at s=13TeV recorded in 2015 by the ATLAS detector at the CERN Large Hadron Collider, corresponding to an integrated luminosity of 3.2 fb-1. No significant excess of events above the Standard Model prediction is observed, and a 95% confidence-level upper limit is derived for the product of the production cross section for pp→ WH times the branching ratio for the decay H→ aa→ 4 b. The upper limit ranges from 6.2 pb for an a-boson mass ma=20GeV to 1.5 pb for ma=60GeV.

  • 308. Aaboudd, M.
    et al.
    Kastanas, Konstatinos A.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Ohm, Christian
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Ripellino, Giulia
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Sidebo, P. Edvin
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L.
    et al.,
    Measurement of tau polarisation in Z/gamma* -> tau tau decays in proton-proton collisions at root s=8 TeV with the ATLAS detector2018Inngår i: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 78, nr 2, artikkel-id 163Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents a measurement of the polarisation of tau leptons produced in Z/gamma* -> tau tau decays which is performed with a dataset of proton-proton collisions at root s = 8 TeV, corresponding to an integrated luminosity of 20.2 fb(-1) recorded with the ATLAS detector at the LHC in 2012. The Z/gamma* -> tau tau decays are reconstructed from a hadronically decaying tau lepton with a single charged particle in the final state, accompanied by a tau lepton that decays leptonically. The tau polarisation is inferred from the relative fraction of energy carried by charged and neutral hadrons in the hadronic tau decays. The polarisation is measured in a fiducial region that corresponds to the kinematic region accessible to this analysis. The tau polarisation extracted over the full phase space within the Z/gamma* mass range of 66 < mZ/gamma* < 116GeVis found to be P-tau = -0.14 +/- 0.02(stat)+/- 0.04(syst). It is in agreement with the Standard Model prediction of Pt = -0.1517 +/- 0.0019, which is obtained from the ALP-GEN event generator interfaced with the PYTHIA 6 parton shower modelling and the TAUOLA tau decay library.

  • 309. Aad, G
    et al.
    Abat, E
    Grahn, Karl-Johan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    Univ Michigan, Dept Phys, Randall Lab.
    zur Nedden, M
    Zutshi, V
    Lafaye, Remi
    Univ Savoie, LAPP, CNTS IN2P3, Annecy Le Vieux, France.
    et, al
    Charged-particle multiplicities in pp interactions at root s=900 GeV measured with the ATLAS detector at the LHC ATLAS Collaboration2010Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 688, nr 1, s. 21-42Artikkel i tidsskrift (Fagfellevurdert)
  • 310. Aad, G
    et al.
    Abbot, B
    Grahn, Karl-Johan
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Strandberg, Jonas
    Univ Michigan, Dept Phys.
    Lafaye, Remi
    Univ Savoie, LAPP, CNTS IN2P3, Annecy Le Vieux, France.
    Zwalinski, L
    et, al
    Observation of a Centrality-Dependent Dijet Asymmetry in Lead-Lead Collisions at root s(NN)=2.76 TeV with the ATLAS Detector at the LHC2010Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 105, nr 25, s. 252303-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    By using the ATLAS detector, observations have been made of a centrality-dependent dijet asymmetry in the collisions of lead ions at the Large Hadron Collider. In a sample of lead-lead events with a per-nucleon center of mass energy of 2.76 TeV, selected with a minimum bias trigger, jets are reconstructed in fine-grained, longitudinally segmented electromagnetic and hadronic calorimeters. The transverse energies of dijets in opposite hemispheres are observed to become systematically more unbalanced with increasing event centrality leading to a large number of events which contain highly asymmetric dijets. This is the first observation of an enhancement of events with such large dijet asymmetries, not observed in proton-proton collisions, which may point to an interpretation in terms of strong jet energy loss in a hot, dense medium.

  • 311. Aad, G.
    et al.
    Dao, V.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Sidebo, P. Edvin
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L.
    et al.,
    Measurement of the differential cross-sections of prompt and non-prompt production of J/psi and psi(2S) in pp collisions at root s=7 and 8 TeV with the ATLAS detector2016Inngår i: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 76, nr 5, artikkel-id 283Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The production rates of prompt and non-prompt J/psi and psi(2S) mesons in their dimuon decay modes are measured using 2.1 and 11.4 fb(-1) of data collected with the ATLAS experiment at the Large Hadron Collider, in proton-proton collisions at root s = 7 and 8 respectively. Production cross-sections for prompt as well as non-prompt sources, ratios of psi(2S) to J/psi production, and the fractions of non-prompt production for J/psi and psi(2S) are measured as a function of meson transverse momentum and rapidity. The measurements are compared to theoretical predictions.

  • 312. Aad, G.
    et al.
    Grahn, Karl-Johan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    Univ Michigan, Dept Phys, Randall Lab.
    Lafaye, Remi
    Univ Savoie, LAPP, CNTS IN2P3, Annecy Le Vieux, France.
    et, al
    Search for New Particles in Two-Jet Final States in 7 TeV Proton-Proton Collisions with the ATLAS Detector at the LHC2010Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 105, nr 16, s. 161801-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A search for new heavy particles manifested as resonances in two-jet final states is presented. The data were produced in 7 TeV proton-proton collisions by the LHC and correspond to an integrated luminosity of 315 nb(-1) collected by the ATLAS detector. No resonances were observed. Upper limits were set on the product of cross section and signal acceptance for excited-quark (q*) production as a function of q* mass. These exclude at the 95% C. L. the q* mass interval 0: 30< m(q)*< 1:26 TeV, extending the reach of previous experiments.

  • 313.
    Aad, G.
    et al.
    Ist Nazl Fis Nucl, Lab Nazl Frascati.
    Grahn, Karl-Johan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    Univ Michigan, Dept Phys.
    Zutshi, V.
    No Illinois Univ, Dept Phys, De Kalb.
    et al.,
    Measurement of inclusive jet and dijet cross sections in proton-proton collisions at 7 TeV centre-of-mass energy with the ATLAS detector2011Inngår i: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 71, nr 2Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Jet cross sections have been measured for the first time in proton-proton collisions at a centre-of-mass energy of 7 TeV using the ATLAS detector. The measurement uses an integrated luminosity of 17 nb(-1) recorded at the Large Hadron Collider. The anti-k(t) algorithm is used to identify jets, with two jet resolution parameters, R = 0.4 and 0.6. The dominant uncertainty comes from the jet energy scale, which is determined to within 7% for central jets above 60 GeV transverse momentum. Inclusive single-jet differential cross sections are presented as functions of jet transverse momentum and rapidity. Dijet cross sections are presented as functions of dijet mass and the angular variable chi. The results are compared to expectations based on next-to-leading-order QCD, which agree with the data, providing a validation of the theory in a new kinematic regime.

  • 314. Aad, G.
    et al.
    Grahn, Karl-Johan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    Univ Michigan, Dept Phys, Ann Arbor.
    Zutshi, V.
    Lafaye, Remi
    Univ Savoie, LAPP, CNTS IN2P3, Annecy Le Vieux, France.
    Performance of the ATLAS detector using first collision data2010Inngår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, nr 9, s. 056-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    More than half a million minimum-bias events of LHC collision data were collected by the ATLAS experiment in December 2009 at centre-of-mass energies of 0.9 TeV and 2.36 TeV. This paper reports on studies of the initial performance of the ATLAS detector from these data. Comparisons between data and Monte Carlo predictions are shown for distributions of several track- and calorimeter-based quantities. The good performance of the ATLAS detector in these first data gives confidence for successful running at higher energies.

  • 315. Aad, G
    et al.
    Grahn, Karl-Johan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    Univ Michigan, Dept Phys, Randall Lab.
    Zutshi, V
    Lafaye, Remi
    Univ Savoie, LAPP, CNTS IN2P3, Annecy Le Vieux, France.
    The ATLAS Simulation Infrastructure2010Inngår i: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 70, nr 3, s. 823-874Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The simulation software for the ATLAS Experiment at the Large Hadron Collider is being used for large-scale production of events on the LHC Computing Grid. This simulation requires many components, from the generators that simulate particle collisions, through packages simulating the response of the various detectors and triggers. All of these components come together under the ATLAS simulation infrastructure. In this paper, that infrastructure is discussed, including that supporting the detector description, interfacing the event generation, and combining the GEANT4 simulation of the response of the individual detectors. Also described are the tools allowing the software validation, performance testing, and the validation of the simulated output against known physics processes.

  • 316. Aad, G
    et al.
    Grahn, Karl-Johan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    Univ Michigan, Dept Phys, Ann Arbor.
    Zutshi, V
    Lafaye, Remi
    Univ Savoie, LAPP, CNTS IN2P3, Annecy Le Vieux, France.
    et, al
    Drift Time Measurement in the ATLAS Liquid Argon Electromagnetic Calorimeter using Cosmic Muons2010Inngår i: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 70, nr 3, s. 755-785Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The ionization signals in the liquid argon of the ATLAS electromagnetic calorimeter are studied in detail using cosmic muons. In particular, the drift time of the ionization electrons is measured and used to assess the intrinsic uniformity of the calorimeter gaps and estimate its impact on the constant term of the energy resolution. The drift times of electrons in the cells of the second layer of the calorimeter are uniform at the level of 1.3% in the barrel and 2.8% in the endcaps. This leads to an estimated contribution to the constant term of (0.29(-0.04)(+0.05))% in the barrel and (0.54(-0.04)(+0.06))% in the endcaps. The same data are used to measure the drift velocity of ionization electrons in liquid argon, which is found to be 4.61 +/- 0.07 mm/mu s at 88.5 K and 1 kV/mm.

  • 317. Aad, G
    et al.
    Grahn, Karl-Johan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    Univ Michigan, Randall Lab .
    Zutshi, V
    Lafaye, Remi
    Univ Savoie, LAPP, CNTS IN2P3, Annecy Le Vieux, France.
    et, al
    Readiness of the ATLAS liquid argon calorimeter for LHC collisions2010Inngår i: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 70, nr 3, s. 723-753Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The ATLAS liquid argon calorimeter has been operating continuously since August 2006. At this time, only part of the calorimeter was readout, but since the beginning of 2008, all calorimeter cells have been connected to the ATLAS readout system in preparation for LHC collisions. This paper gives an overview of the liquid argon calorimeter performance measured in situ with random triggers, calibration data, cosmic muons, and LHC beam splash events. Results on the detector operation, timing performance, electronics noise, and gain stability are presented. High energy deposits from radiative cosmic muons and beam splash events allow to check the intrinsic constant term of the energy resolution. The uniformity of the electromagnetic barrel calorimeter response along eta (averaged over phi) is measured at the percent level using minimum ionizing cosmic muons. Finally, studies of electromagnetic showers from radiative muons have been used to cross-check the Monte Carlo simulation. The performance results obtained using the ATLAS readout, data acquisition, and reconstruction software indicate that the liquid argon calorimeter is well-prepared for collisions at the dawn of the LHC era.

  • 318. Aad, G
    et al.
    Grahn, Karl-Johan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    Univ Michigan, Dept Phys.
    Zutshi, V
    Lafaye, Remi
    Univ Savoie, LAPP, CNTS IN2P3, Annecy Le Vieux, France.
    et, al
    Readiness of the ATLAS Tile Calorimeter for LHC collisions2010Inngår i: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 70, nr 4, s. 1193-1236Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Tile hadronic calorimeter of the ATLAS detector has undergone extensive testing in the experimental hall since its installation in late 2005. The readout, control and calibration systems have been fully operational since 2007 and the detector has successfully collected data from the LHC single beams in 2008 and first collisions in 2009. This paper gives an overview of the Tile Calorimeter performance as measured using random triggers, calibration data, data from cosmic ray muons and single beam data. The detector operation status, noise characteristics and performance of the calibration systems are presented, as well as the validation of the timing and energy calibration carried out with minimum ionising cosmic ray muons data. The calibration systems' precision is well below the design value of 1%. The determination of the global energy scale was performed with an uncertainty of 4%.

  • 319. Aad, G.
    et al.
    Grahn, Karl-Johan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    Univ Michigan, Dept Phys.
    Zutshi, V.
    Lafaye, Remi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    et, al
    Search for quark contact interactions in dijet angular distributions in pp collisions at root s=7 TeV measured with the ATLAS detector2011Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 694, nr 4/5, s. 327-345Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Dijet angular distributions from the first LHC pp collisions at center-of-mass energy root s = 7 TeV have been measured with the ATLAS detector. The dataset used for this analysis represents an integrated luminosity of 3.1 pb(-1). Dijet chi distributions and centrality ratios have been measured up to dijet masses of 2.8 TeV, and found to be in good agreement with Standard Model predictions. Analysis of the chi distributions excludes quark contact interactions with a compositeness scale Lambda below 3.4 TeV, at 95% confidence level, significantly exceeding previous limits.

  • 320. Aad, G.
    et al.
    Grahn, Karl-Johan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    Univ Michigan, Dept Phys.
    Zutshi, V.
    Lafaye, Remi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    et, al
    Studies of the performance of the ATLAS detector using cosmic-ray muons2011Inngår i: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 71, nr 3, s. 1593-Artikkel i tidsskrift (Fagfellevurdert)
  • 321. Aad, G
    et al.
    Grahn, Karl-Johan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    Univ Michigan, Dept Phys, Randall Lab.
    Zutshi, V
    Lafaye, Remi
    Univ Savoie, LAPP, CNTS IN2P3, Annecy Le Vieux, France.
    et, al
    The ATLAS Inner Detector commissioning and calibration2010Inngår i: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 70, nr 3, s. 787-821Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The ATLAS Inner Detector is a composite tracking system consisting of silicon pixels, silicon strips and straw tubes in a 2 T magnetic field. Its installation was completed in August 2008 and the detector took part in data-taking with single LHC beams and cosmic rays. The initial detector operation, hardware commissioning and in-situ calibrations are described. Tracking performance has been measured with 7.6 million cosmic-ray events, collected using a tracking trigger and reconstructed with modular pattern-recognition and fitting software. The intrinsic hit efficiency and tracking trigger efficiencies are close to 100%. Lorentz angle measurements for both electrons and holes, specific energy-loss calibration and transition radiation turn-on measurements have been performed. Different alignment techniques have been used to reconstruct the detector geometry. After the initial alignment, a transverse impact parameter resolution of 22.1 +/- 0.9 mu m and a relative momentum resolution sigma (p) /p=(4.83 +/- 0.16)x10(-4) GeV(-1)xp (T) have been measured for high momentum tracks.

  • 322. Aad, G
    et al.
    Grahn, Karl-Johan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    Univ Michigan, Dept Phys, Randall Lab .
    Zutshia, V
    Lafaye, Remi
    Univ Savoie, LAPP, CNTS IN2P3, Annecy Le Vieux, France.
    et, al
    Commissioning of the ATLAS Muon Spectrometer with cosmic rays2010Inngår i: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 70, nr 3, s. 875-916Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The ATLAS detector at the Large Hadron Collider has collected several hundred million cosmic ray events during 2008 and 2009. These data were used to commission the Muon Spectrometer and to study the performance of the trigger and tracking chambers, their alignment, the detector control system, the data acquisition and the analysis programs. We present the performance in the relevant parameters that determine the quality of the muon measurement. We discuss the single element efficiency, resolution and noise rates, the calibration method of the detector response and of the alignment system, the track reconstruction efficiency and the momentum measurement. The results show that the detector is close to the design performance and that the Muon Spectrometer is ready to detect muons produced in high energy proton-proton collisions.

  • 323. Aad, G.
    et al.
    Grahn, Karl-Johan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L.
    et al.,
    Measurement of the W(+)W(-) Cross Section in root s=7 TeV pp Collisions with ATLAS2011Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 107, nr 4, s. 041802-1-041802-18Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This Letter presents a measurement of the W(+)W(-) production cross section in root s = 7 TeV pp collisions by the ATLAS experiment, using 34 pb(-1) of integrated luminosity produced by the Large Hadron Collider at CERN. Selecting events with two isolated leptons, each either an electron or a muon, 8 candidate events are observed with an expected background of 1.7 +/- 0.6 events. The measured cross section is 41(-16)(+20)(stat) +/- 5(syst) +/- 1(lumi) pb, which is consistent with the standard model prediction of 44 +/- 3 pb calculated at next-to-leading order in QCD.

  • 324. Aad, G.
    et al.
    Grahn, Karl-Johan
    DESY, D-2000 Hamburg, Germany .
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L.
    et al.,
    Properties of jets measured from tracks in proton-proton collisions at center-of-mass energy root s=7 TeV with the ATLAS detector2011Inngår i: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 84, nr 5, s. 054001-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

     Jets are identified and their properties studied in center-of-mass energy root s = 7 TeV proton-proton collisions at the Large Hadron Collider using charged particles measured by the ATLAS inner detector. Events are selected using a minimum bias trigger, allowing jets at very low transverse momentum to be observed and their characteristics in the transition to high-momentum fully perturbative jets to be studied. Jets are reconstructed using the anti-k(t) algorithm applied to charged particles with two radius parameter choices, 0.4 and 0.6. An inclusive charged jet transverse momentum cross section measurement from 4 GeV to 100 GeV is shown for four ranges in rapidity extending to 1.9 and corrected to charged particle-level truth jets. The transverse momenta and longitudinal momentum fractions of charged particles within jets are measured, along with the charged particle multiplicity and the particle density as a function of radial distance from the jet axis. Comparison of the data with the theoretical models implemented in existing tunings of Monte Carlo event generators indicates reasonable overall agreement between data and Monte Carlo. These comparisons are sensitive to Monte Carlo parton showering, hadronization, and soft physics models.

  • 325. Aad, G.
    et al.
    Grahn, Karl-Johan
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L.
    et al.,
    Search for a heavy neutral particle decaying into an electron and a muon using 1 fb(-1) of ATLAS data2011Inngår i: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 71, nr 12, s. 1809-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A search is presented for a high mass neutral particle that decays directly to the e(+/-) mu(-/+) final state. The data sample was recorded by the ATLAS detector in root s = 7 TeV pp collisions at the LHC from March to June 2011 and corresponds to an integrated luminosity of 1.07 fb(-1). The data are found to be consistent with the Standard Model background. The high e(+/-) mu(-/+) mass region is used to set 95% confidence level upper limits on the production of two possible new physics processes: tau sneutrinos in an R-parity violating supersymmetric model and Z'-like vector bosons in a lepton flavor violating model.

  • 326. Aad, G.
    et al.
    Grahn, Karl-Johan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    University of Chicago.
    Zwalinski, L.
    et al.,
    Search for a Heavy Particle Decaying into an Electron and a Muon with the ATLAS Detector in root s=7 TeV pp collisions at the LHC2011Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 106, nr 25, s. 251801-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This Letter presents the first search for a heavy particle decaying into an e(+/-)mu(-/+) final state in root s = 7 TeV pp collisions at the LHC. The data were recorded by the ATLAS detector during 2010 and correspond to a total integrated luminosity of 35 pb(-1). No excess above the standard model background expectation is observed. Exclusions at 95% confidence level are placed on two representative models. In an R-parity violating supersymmetric model, tau sneutrinos with a mass below 0.75 TeV are excluded, assuming all R-parity violating couplings are zero except lambda(311)' = 0.11 and lambda(312) = 0.07. In a lepton flavor violating model, a Z'-like vector boson with masses of 0.70-1.00 TeV and corresponding cross sections times branching ratios of 0.175-0.183 pb is excluded. These results extend to higher mass R-parity violating sneutrinos and lepton flavor violating Z's than previous constraints from the Tevatron.

  • 327. Aad, G.
    et al.
    Grahn, Karl-Johan
    DESY, D-2000 Hamburg, Germany .
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L.
    et al.,
    Search for a Standard Model Higgs Boson in the H -> ZZ -> l(+)l(-)v(v)over-bar Decay Channel with the ATLAS Detector2011Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 107, nr 22, s. 221802-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A search for a heavy standard model Higgs boson decaying via H -> ZZ -> l(+)l(-)v (v) over bar, where l = e, mu, is presented. It is based on proton-proton collision data at root s = 7 TeV, collected by the ATLAS experiment at the LHC in the first half of 2011 and corresponding to an integrated luminosity of 1.04 fb(-1). The data are compared to the expected standard model backgrounds. The data and the background expectations are found to be in agreement and upper limits are placed on the Higgs boson production cross section over the entire mass window considered; in particular, the production of a standard model Higgs boson is excluded in the region 340 < m(H) < 450 GeV at the 95% confidence level.

  • 328. Aad, G.
    et al.
    Grahn, Karl-Johan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    University of Chicago.
    Zwalinski, L
    et al.,
    Search for an excess of events with an identical flavour lepton pair and significant missing transverse momentum in root s=7 TeV proton-proton collisions with the ATLAS detector2011Inngår i: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 71, nr 7, s. 1647-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Results are presented of a search for particles decaying into final states with significant missing transverse momentum and exactly two identical flavour leptons (e, mu) of opposite charge in root s = 7 TeV collisions at the Large Hadron Collider. This channel is particularly sensitive to supersymmetric particle cascade decays producing flavour correlated lepton pairs. Flavour uncorrelated backgrounds are subtracted using a sample of opposite flavour lepton pair events. Observation of an excess beyond Standard Model expectations following this subtraction procedure would offer one of the best routes to measuring the masses of supersymmetric particles. In a data sample corresponding to an integrated luminosity of 35 pb(-1) no such excess is observed. Model-independent limits are set on the contribution to these final states from supersymmetry and are used to exclude regions of a phenomenological supersymmetric parameter space.

  • 329. Aad, G.
    et al.
    Grahn, Karl-Johan
    DESY, D-2000 Hamburg, Germany .
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L.
    et al.,
    Search for massive colored scalars in four-jet final states in root s=7 TeV proton-proton collisions with the ATLAS detector2011Inngår i: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 71, nr 12, s. 1828-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A search for pair-produced scalar particles decaying to a four-jet final state is presented. The analysis is performed using an integrated luminosity of 34 pb(-1) recorded by the ATLAS detector in 2010. No deviation from the Standard Model is observed. For a scalar mass of 100 GeV (190 GeV) the limit on the scalar gluon pair production cross section at 95% confidence level is 1 nb (0.28 nb). When these results are interpreted as mass limits, scalar-gluons (hyperpions) with masses of 100 to 185 GeV (100 to 155 GeV) are excluded at 95% confidence level with the exception of a mass window of width about 5 GeV (15 GeV) around 140 GeV.

  • 330. Aad, G.
    et al.
    Grahn, Karl-Johan
    DESY, D-2000 Hamburg, Germany .
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L.
    et al.,
    Search for the Higgs Boson in the H -> WW -> l nu jj Decay Channel in pp Collisions at root s=7 TeV with the ATLAS Detector2011Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 107, nr 23, s. 231801-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A search for a Higgs boson has been performed in the H -> WW -> l nu jj channel in 1.04 fb(-1) of pp collision data at root s = 7 TeV recorded with the ATLAS detector at the Large Hadron Collider. No significant excess of events is observed over the expected background and limits on the Higgs boson production cross section are derived for a Higgs boson mass in the range 240 GeV < m(H) < 600 GeV. The best sensitivity is reached for m(H) = 400 GeV, where the 95% confidence level upper bound on the cross section for H -> WW production is 3.1 pb, or 2.7 times the standard model prediction.

  • 331. Aad, G.
    et al.
    Grahn, Karl-Johan
    DESY, D-2000 Hamburg, Germany .
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L.
    et al.,
    Search for the Standard Model Higgs boson in the two photon decay channel with the ATLAS detector at the LHC2011Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 705, nr 5, s. 452-470Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A search for the Standard Model Higgs boson in the two photon decay channel is reported, using 1.08 fb(-1) of proton-proton collision data at a centre-of-mass energy of 7 TeV recorded by the ATLAS detector. No significant excess is observed in the investigated mass range of 110-150 GeV. Upper limits on the cross-section,times branching ratio of between 2.0 and 5.8 times the Standard Model prediction are derived for this mass range.

  • 332. Aad, G.
    et al.
    Grahn, Karl-Johan
    DESY, D-2000 Hamburg, Germany .
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L.
    Lafaye, Remi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Measurement of the upsilon(1S) production cross-section in pp collisions at root s=7 TeV in ATLAS ATLAS Collaboration2011Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 705, nr 1-2, s. 9-27Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A measurement of the cross-section for upsilon(1S) -> mu(+)mu(-) production in proton-proton collisions at centre of mass energy of 7 TeV is presented. The cross-section is measured as a function of the upsilon(1S) transverse momentum in two bins of rapidity, vertical bar y(upsilon(1S))vertical bar < 1.2 and 1.2 < vertical bar y(upsilon(1S))vertical bar < 2.4. The measurement requires that both muons have transverse momentum p(T)(mu) > 4 GeV and pseuclorapidity vertical bar eta(mu)vertical bar < 2.5 in order to reduce theoretical uncertainties on the acceptance, which depend on the poorly known polarisation. The results are based on an integrated luminosity of 1.13 pb(-1), collected with the ATLAS detector at the Large Hadron Collider. The cross-section measurement is compared to theoretical predictions: it agrees to within a factor of two with a prediction based on the NRQCD model including colour-singlet and colour-octet matrix elements as implemented in PYTHIA while it disagrees by up to a factor of ten with the next-to-leading order prediction based on the colour-singlet model.

  • 333. Aad, G.
    et al.
    Grahn, Karl-Johan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    University of Chicago.
    Zwalinski, L.
    Lafaye, Remi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Search for Diphoton Events with Large Missing Transverse Energy in 7 TeV Proton-Proton Collisions with the ATLAS Detector2011Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 106, nr 12, s. 121803-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A search for diphoton events with large missing transverse energy is presented. The data were collected with the ATLAS detector in proton-proton collisions at root s = 7 TeV at the CERN Large Hadron Collider and correspond to an integrated luminosity of 3: 1 pb(-1). No excess of such events is observed above the standard model background prediction. In the context of a specific model with one universal extra dimension with compactification radius R and gravity-induced decays, values of 1/R < 729 GeV are excluded at 95% C. L., providing the most sensitive limit on this model to date.

  • 334. Aad, G.
    et al.
    Grahn, Karl-Johan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    University of Chicago.
    Zwalinski, L.
    Lafaye, Remi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    et, al
    A search for new physics in dijet mass and angular distributions in pp collisions at root s=7 TeV measured with the ATLAS detector2011Inngår i: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 13, s. 053044-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A search for new interactions and resonances produced in LHC proton-proton (pp) collisions at a centre-of-mass energy root s = 7 TeV was performed with the ATLAS detector. Using a dataset with an integrated luminosity of 36 pb(-1), dijet mass and angular distributions were measured up to dijet masses of similar to 3.5 TeV and were found to be in good agreement with Standard Model predictions. This analysis sets limits at 95% CL on various models for new physics: an excited quark is excluded for mass between 0.60 and 2.64 TeV, an axigluon hypothesis is excluded for axigluon masses between 0.60 and 2.10 TeV and quantum black holes are excluded in models with six extra space-time dimensions for quantum gravity scales between 0.75 and 3.67 TeV. Production cross section limits as a function of dijet mass are set using a simplified Gaussian signal model to facilitate comparisons with other hypotheses. Analysis of the dijet angular distribution using a novel technique simultaneously employing the dijet mass excludes quark contact interactions with a compositeness scale 3 below 9.5 TeV.

  • 335. Aad, G.
    et al.
    Grahn, Karl-Johan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    University of Chicago.
    Zwalinski, L.
    Lafaye, Remi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    et, al
    Charged-particle multiplicities in pp interactions measured with the ATLAS detector at the LHC2011Inngår i: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 13, s. 053033-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Measurements are presented from proton-proton collisions at centre-of-mass energies of root s = 0.9, 2.36 and 7 TeV recorded with the ATLAS detector at the LHC. Events were collected using a single-arm minimum-bias trigger. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity and the relationship between the mean transverse momentum and charged-particle multiplicity are measured. Measurements in different regions of phase space are shown, providing diffraction-reduced measurements as well as more inclusive ones. The observed distributions are corrected to well-defined phase-space regions, using model-independent corrections. The results are compared to each other and to various Monte Carlo (MC) models, including a new AMBT1 pythia6 tune. In all the kinematic regions considered, the particle multiplicities are higher than predicted by the MC models. The central charged-particle multiplicity per event and unit of pseudorapidity, for tracks with p(T) > 100 MeV, is measured to be 3.483 +/- 0.009 (stat) +/- 0.106 (syst) at root s = 0.9 TeV and 5.630 +/- 0.003 (stat) +/- 0.169 (syst) at root s = 7 TeV.

  • 336. Aad, G.
    et al.
    Grahn, Karl-Johan
    DESY, D-2000 Hamburg, Germany .
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L.
    Lafaye, Remi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    et, al
    Limits on the production of the standard model Higgs boson in pp collisions at root s=7 TeV with the ATLAS detector2011Inngår i: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 71, nr 9, s. 1728-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A search for the Standard Model Higgs boson at the Large Hadron Collider (LHC) running at a centre-of-mass energy of 7 TeV is reported, based on a total integrated luminosity of up to 40 pb(-1) collected by the ATLAS detector in 2010. Several Higgs boson decay channels: H -> gamma gamma, H -> ZZ(()*()) -> llll, H -> ZZ -> LL nu nu, H -> ZZ -> llqq, H -> WW(()*()) -> l nu l nu and H -> WW -> l nu qq (l is e, mu) are combined in a mass range from 110 GeV to 600 GeV. The highest sensitivity is achieved in the mass range between 160 GeV and 170 GeV, where the expected 95% CL exclusion sensitivity is at Higgs boson production cross sections 2.3 times the Standard Model prediction. Upper limits on the cross section for its production are determined. Models with a fourth generation of heavy leptons and quarks with Standard Model-like couplings to the Higgs boson are also investigated and are excluded at 95% CL for a Higgs boson mass in the range from 140 GeV to 185 GeV.

  • 337. Aad, G.
    et al.
    Grahn, Karl-Johan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    University of Chicago.
    Zwalinski, L.
    Lafaye, Remi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    et, al
    Luminosity determination in pp collisions at root s=7 TeV using the ATLAS detector at the LHC2011Inngår i: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 71, nr 4, s. 1630-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Measurements of luminosity obtained using the ATLAS detector during early running of the Large Hadron Collider (LHC) at root s = 7 TeV are presented. The luminosity is independently determined using several detectors and multiple algorithms, each having different acceptances, systematic uncertainties and sensitivity to background. The ratios of the luminosities obtained from these methods are monitored as a function of time and of mu, the average number of inelastic interactions per bunch crossing. Residual time- and mu-dependence between the methods is less than 2% for 0 < mu < 2.5. Absolute luminosity calibrations, performed using beam separation scans, have a common systematic uncertainty of +/- 11%, dominated by the measurement of the LHC beam currents. After calibration, the luminosities obtained from the different methods differ by at most +/- 2%. The visible cross sections measured using the beam scans are compared to predictions obtained with the PYTHIA and PHOJET event generators and the ATLAS detector simulation.

  • 338. Aad, G.
    et al.
    Grahn, Karl-Johan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    University of Chicago.
    Zwalinski, L.
    Lafaye, Remi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    et, al.
    Measurement of Dijet Azimuthal Decorrelations in pp Collisions at root s=7 TeV2011Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 106, nr 17, s. 172002-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Azimuthal decorrelations between the two central jets with the largest transverse momenta are sensitive to the dynamics of events with multiple jets. We present a measurement of the normalized differential cross section based on the full data set ( integral Ldt = 36 pb(-1)) acquired by the ATLAS detector during the 2010 root s = 7 TeV proton-proton run of the LHC. The measured distributions include jets with transverse momenta up to 1.3 TeV, probing perturbative QCD in a high-energy regime.

  • 339. Aad, G.
    et al.
    Grahn, Karl-Johan
    DESY, D-2000 Hamburg, Germany .
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L.
    Lafaye, Remi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    et, al
    Measurement of dijet production with a veto on additional central jet activity in pp collisions at root s=7 TeV using the ATLAS detector2011Inngår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, nr 9, s. 053-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A measurement of jet activity in the rapidity interval bounded by a dijet system is presented. Events are vetoed if a jet with transverse momentum greater than 20 GeV is found between the two boundary jets. The fraction of dijet events that survive the jet veto is presented for boundary jets that are separated by up to six units of rapidity and with mean transverse momentum 50 < <(p)over bar>T < 500 GeV. The mean multiplicity of jets above the veto scale in the rapidity interval bounded by the dijet system is also presented as an alternative method for quantifying perturbative QCD emission. The data are compared to a next-to-leading order plus parton shower prediction from the POWHEG-BOX, an all-order resummation using the HEJ calculation and the PYTHIA, HERWIG++ and ALPGEN event generators. The measurement was performed using pp collisions at root s = 7 TeV using data recorded by the ATLAS detector in 2010.

  • 340. Aad, G.
    et al.
    Grahn, Karl-Johan
    DESY, D-2000 Hamburg, Germany .
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L
    Lafaye, Remi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    et, al
    Measurement of multi-jet cross sections in proton-proton collisions at a 7 TeV center-of-mass energy2011Inngår i: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 71, nr 11, s. 1763-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

     Inclusive multi-jet production is studied in proton-proton collisions at a center-of-mass energy of 7 TeV, using the ATLAS detector. The data sample corresponds to an integrated luminosity of 2.4 pb(-1). Results on multi-jet cross sections are presented and compared to both leading-order plus parton-shower Monte Carlo predictions and to next-to-leading-order QCD calculations.

  • 341. Aad, G.
    et al.
    Grahn, Karl-Johan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    University of Chicago.
    Zwalinski, L.
    Lafaye, Remi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    et, al
    Measurement of the centrality dependence of J/psi yields and observation of Z production in lead-lead collisions with the ATLAS detector at the LHC2011Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 697, nr 4, s. 294-312Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Using the ATLAS detector, a centrality-dependent suppression has been observed in the yield of J/psi mesons produced in the collisions of lead ions at the Large Hadron Collider. In a sample of minimum-bias lead-lead collisions at a nucleon-nucleon centre of mass energy root s(NN) = 2.76 TeV, corresponding to an integrated luminosity of about 6.7 mu b(-1), J/psi mesons are reconstructed via their decays to mu(+)mu(-) pairs. The measured J/psi yield, normalized to the number of binary nucleon-nucleon collisions, is found to significantly decrease from peripheral to central collisions. The centrality dependence is found to be qualitatively similar to the trends observed at previous, lower energy experiments. The same sample is used to reconstruct Z bosons in the mu(+)mu(-) final state, and a total of 38 candidates are selected in the mass window of 66 to 116 GeV. The relative Z yields as a function of centrality are also presented, although no conclusion can be inferred about their scaling with the number of binary collisions, because of limited statistics. This analysis provides the first results on J/psi and Z production in lead-lead collisions at the LHC.

  • 342. Aad, G.
    et al.
    Grahn, Karl-Johan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    University of Chicago.
    Zwalinski, L.
    Lafaye, Remi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    et, al
    Measurement of the differential cross-sections of inclusive, prompt and non-prompt J/psi production in proton-proton collisions at root s=7 TeV2011Inngår i: Nuclear Physics B, ISSN 0550-3213, E-ISSN 1873-1562, Vol. 850, nr 3, s. 387-444Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The inclusive J/psi production cross-section and fraction of J/psi mesons produced in B-hadron decays are measured in proton proton collisions at root s = 7 TeV with the ATLAS detector at the LHC, as a function of the transverse momentum and rapidity of the J/psi, using 2.3 pb(-1) of integrated luminosity. The cross-section is measured from a minimum P(T) of 1 GeV to a maximum of 70 GeV and for rapidities within vertical bar y vertical bar < 2.4 giving the widest reach of any measurement of J/psi production to date. The differential production cross-sections of prompt and non-prompt J/psi are separately determined and are compared to Colour Singlet NNLO*, Colour Evaporation Model, and FONLL predictions.

  • 343. Aad, G.
    et al.
    Grahn, Karl-Johan
    DESY, D-2000 Hamburg, Germany .
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L.
    Lafaye, Remi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    et, al
    Measurement of the inclusive isolated prompt photon cross-section in pp collisions at root s=7 TeV using 35 pb(-1) of ATLAS data2011Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 706, nr 2-3, s. 150-167Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A measurement of the differential cross-section for the inclusive production of isolated prompt photons in pp collisions at a center-of-mass energy root s = 7 TeV is presented. The measurement covers the pseudorapidity ranges vertical bar eta vertical bar < 1.37 and 1.52 <= vertical bar eta vertical bar < 2.37 in the transverse energy range 45 <= E(T) < 400 GeV. The results are based on an integrated luminosity of 35 pb(-1), collected with the ATLAS detector at the LHC. The yields of the signal photons are measured using a data-driven technique, based on the observed distribution of the hadronic energy in a narrow cone around the photon candidate and the photon selection criteria. The results are compared with next-to-leading order perturbative QCD calculations and found to be in good agreement over four orders of magnitude in cross-section.

  • 344. Aad, G.
    et al.
    Grahn, Karl-Johan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    University of Chicago.
    Zwalinski, L.
    Lafaye, Remi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    et, al
    Measurement of the inelastic proton-proton cross-section at root s=7 TeV with the ATLAS detector2011Inngår i: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 2, s. 463-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The dependence of the rate of proton-proton interactions on the centre-of-mass collision energy, root s, is of fundamental importance for both hadron collider physics and particle astrophysics. The dependence cannot yet be calculated from first principles; therefore, experimental measurements are needed. Here we present the first measurement of the inelastic proton-proton interaction cross-section at a centre-of-mass energy, root s, of 7 TeV using the ATLAS detector at the Large Hadron Collider. Events are selected by requiring hits on scintillation counters mounted in the forward region of the detector. An inelastic crosssection of 60.3 +/- 2.1 mb is measured for xi > 5x10(-6), where xi is calculated from the invariant mass, M(X), of hadrons selected using the largest rapidity gap in the event. For diffractive events, this corresponds to requiring at least one of the dissociation masses to be larger than 15.7 GeV.

  • 345. Aad, G.
    et al.
    Grahn, Karl-Johan
    DESY, D-2000 Hamburg, Germany .
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L
    Lafaye, Remi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    et, al
    Measurement of the jet fragmentation function and transverse profile in proton-proton collisions at a center-of-mass energy of 7 TeV with the ATLAS detector2011Inngår i: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 71, nr 11, s. 1795-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

     The jet fragmentation function and transverse profile for jets with 25 GeV < p(Tjet) < 500 GeV and |eta(jet)| < 1.2 produced in proton-proton collisions with a center-of-mass energy of 7 TeV are presented. The measurement is performed using data with an integrated luminosity of 36 pb(-1). Jets are reconstructed and their momentum measured using calorimetric information. The momenta of the charged particle constituents are measured using the tracking system. The distributions corrected for detector effects are compared with various Monte Carlo event generators and generator tunes. Several of these choices show good agreement with the measured fragmentation function. None of these choices reproduce both the transverse profile and fragmentation function over the full kinematic range of the measurement.  

  • 346. Aad, G.
    et al.
    Grahn, Karl-Johan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    University of Chicago.
    Zwalinski, L.
    Lafaye, Remi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    et, al
    Measurement of the production cross section for W-bosons in association with jets in pp collisions at root s=7 TeV with the ATLAS detector2011Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 698, nr 5, s. 325-345Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This Letter reports on a first measurement of the inclusive W + jets cross section in proton-proton collisions at a centre-of-mass energy of 7 TeV at the LHC, with the ATLAS detector. Cross sections, in both the electron and muon decay modes of the W-boson, are presented as a function of jet multiplicity and of the transverse momentum of the leading and next-to-leading jets in the event. Measurements are also presented of the ratio of cross sections sigma (W + >= n)/sigma(W + >= n - 1) for inclusive jet multiplicities n = 1-4. The results, based on an integrated luminosity of 1.3 pb(-1), have been corrected for all known detector effects and are quoted in a limited and well-defined range of jet and lepton kinematics. The measured cross sections are compared to particle-level predictions based on perturbative QCD. Next-to-leading order calculations, studied here for n <= 2, are found in good agreement with the data. Leading-order multiparton event generators, normalized to the NNLO total cross section, describe the data well for all measured jet multiplicities.

  • 347. Aad, G.
    et al.
    Grahn, Karl-Johan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    Univ Michigan, Dept Phys, Ann Arbor.
    Zwalinski, L.
    Lafaye, Remi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    et, al
    Measurement of the top quark-pair production cross section with ATLAS in pp collisions at root s=7 TeV2011Inngår i: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 71, nr 3, s. 1577-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A measurement of the production cross-section for top quark pairs (t (t) over bar) in pp collisions at root s = 7 TeV is presented using data recorded with the ATLAS detector at the Large Hadron Collider. Events are selected in two different topologies: single lepton (electron e or muon mu) with large missing transverse energy and at least four jets, and dilepton (ee, mu mu or e mu) with large missing transverse energy and at least two jets. In a data sample of 2.9 pb(-1), 37 candidate events are observed in the single-lepton topology and 9 events in the dilepton topology. The corresponding expected backgrounds from non-t (t) over bar Standard Model processes are estimated using data-driven methods and determined to be 12.2 +/- 3.9 events and 2.5 +/- 0.6 events, respectively. The kinematic properties of the selected events are consistent with SM t (t) over bar production. The inclusive top quark pair production cross-section is measured to besigma(t (t) over bar) = 145 +/- 31 (stat.)(-27)(+42) (syst.) pb.The measurement agrees with perturbative QCD calculations.

  • 348. Aad, G.
    et al.
    Grahn, Karl-Johan
    DESY, D-2000 Hamburg, Germany .
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L.
    Lafaye, Remi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    et, al
    Measurement of the transverse momentum distribution of Z/gamma* bosons in proton-proton collisions at root s=7 TeV with the ATLAS detector2011Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 705, nr 5, s. 415-434Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A measurement of the Z/gamma* transverse momentum (p(T)(Z)) distribution in proton-proton collisions at root s = 7 TeV is presented using Z/gamma* -> e(+)e(-) and Z/gamma* -> mu(+)mu(-) decays collected with the ATLAS detector in data sets with integrated luminosities of 35 pb(-1) and 40 pb(-1), respectively. The normalized differential cross sections are measured separately for electron and muon decay channels as well as for their combination up to pi of 350 GeV for invariant dilepton masses 66 GeV < m(ll) < 116 GeV. The measurement is compared to predictions of perturbative QCD and various event generators. The prediction of resummed QCD combined with fixed order perturbative QCD is found to be in good agreement with the data.

  • 349. Aad, G.
    et al.
    Grahn, Karl-Johan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    University of Chicago.
    Zwalinski, L.
    Lafaye, Remi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    et, al
    Measurement of the W charge asymmetry in the W -> mu nu decay mode in pp collisions at root s=7 TeV with the ATLAS detector2011Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 701, nr 1, s. 31-49Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This Letter reports a measurement of the muon charge asymmetry from W bosons produced in proton-proton collisions at a centre-of-mass energy of 7 TeV with the ATLAS experiment at the LHC. The asymmetry is measured in the W -> mu nu decay mode as a function of the muon pseudorapidity using a data sample corresponding to a total integrated luminosity of 31 pb(-1). The results are compared to predictions based on next-to-leading order calculations with various parton distribution functions. This measurement provides information on the u and d quark momentum fractions in the proton.

  • 350. Aad, G.
    et al.
    Grahn, Karl-Johan
    DESY, D-2000 Hamburg, Germany .
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L.
    Lafaye, Remi
    et al.,
    Measurement of the Z -> tau tau cross section with the ATLAS detector2011Inngår i: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 84, nr 11, s. 112006-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Z -> tau tau cross section is measured with the ATLAS experiment at the LHC in four different final states determined by the decay modes of the tau leptons: muon-hadron, electron-hadron, electron-muon, and muon-muon. The analysis is based on a data sample corresponding to an integrated luminosity of 36 pb(-1), at a proton-proton center-of-mass energy of root s = 7 TeV. Cross sections are measured separately for each final state in fiducial regions of high detector acceptance, as well as in the full phase space, over the mass region 66-116 GeV. The individual cross sections are combined and the product of the total Z production cross section and Z -> tau tau branching fraction is measured to be 0.97 +/- 0.07(stat) +/- 0.06(syst) +/- 0: 03(lumi) nb, in agreement with next-to-next-to-leading order calculations.

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