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  • 351. Aad, G.
    et al.
    Grahn, Karl-Johan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Lund-Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    University of Chicago.
    Zwalinski, L.
    Lafaye, Remi
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    et, al
    Measurements of underlying-event properties using neutral and charged particles in pp collisions at root s=900 GeV and root s=7 TeV with the ATLAS detector at the LHC2011In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 71, no 5, p. 1636-Article in journal (Refereed)
    Abstract [en]

    We present first measurements of charged and neutral particle-flow correlations in pp collisions using the ATLAS calorimeters. Data were collected in 2009 and 2010 at centre-of-mass energies of 900 GeV and 7 TeV. Events were selected using a minimum-bias trigger which required a charged particle in scintillation counters on either side of the interaction point. Particle flows, sensitive to the underlying event, are measured using clusters of energy in the ATLAS calorimeters, taking advantage of their fine granularity. No Monte Carlo generator used in this analysis can accurately describe the measurements. The results are independent of those based on charged particles measured by the ATLAS tracking systems and can be used to constrain the parameters of Monte Carlo generators.

  • 352. Aad, G.
    et al.
    Grahn, Karl-Johan
    Ist Nazl Fis Nucl, Lab Nazl Frascati, I-00044 Frascati, Italy .
    Lund-Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    Lafaye, Remi
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    et, al
    Search for a heavy gauge boson decaying to a charged lepton and a neutrino in 1 fb(-1) of pp collisions at root s=7 TeV using the ATLAS detector ATLAS Collaboration2011In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 705, no 1-2, p. 28-46Article in journal (Refereed)
    Abstract [en]

    The ATLAS detector at the LHC is used to search for high-mass states, such as heavy charged gauge bosons (W '), decaying to a charged lepton (electron or muon) and a neutrino. Results are presented based on the analysis of pp collisions at a center-of-mass energy of 7 TeV corresponding to an integrated luminosity of 1.04 fb(-1). No excess above Standard Model expectations is observed. A W ' with Sequential Standard Model couplings is excluded at the 95% confidence level for masses up to 2.15 TeV.

  • 353.
    Aad, G.
    et al.
    Univ Freiburg.
    Grahn, Karl-Johan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Lund-Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    Lafaye, Remi
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    et, al
    Search for contact interactions in dimuon events from pp collisions at root s=7 TeV with the ATLAS detector2011In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 84, no 1, p. 011101-Article in journal (Refereed)
    Abstract [en]

    A search for contact interactions has been performed using dimuon events recorded with the ATLAS detector in proton-proton collisions at root s = 7 TeV. The data sample corresponds to an integrated luminosity of 42 pb(-1). No significant deviation from the standard model is observed in the dimuon mass spectrum, allowing the following 95% C. L. limits to be set on the energy scale of contact interactions: Lambda > 4: 9 TeV (4.5 TeV) for constructive (destructive) interference in the left-left isoscalar compositeness model. These limits are the most stringent to date for mu mu qq contact interactions.

  • 354. Aad, G.
    et al.
    Grahn, Karl-Johan
    DESY, D-2000 Hamburg, Germany .
    Lund-Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    Lafaye, Remi
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    et, al
    Search for diphoton events with large missing transverse energy with 36 pb(-1) of 7 TeV proton-proton collision data with the ATLAS detector2011In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 71, no 10, p. 1744-Article in journal (Refereed)
    Abstract [en]

    Making use of 36 pb(-1) of proton-proton collision data at root s = 7 TeV, the ATLAS Collaboration has performed a search for diphoton events with large missing transverse energy. Observing no excess of events above the Standard Model prediction, a 95% Confidence Level ( CL) upper limit is set on the cross section for new physics of sigma < 0.38-0.65 pb in the context of a generalised model of gauge-mediated supersymmetry breaking (GGM) with a bino-like lightest neutralino, and of sigma < 0.18-0.23 pb in the context of a specific model with one universal extra dimension (UED). A 95% CL lower limit of 560 GeV, for bino masses above 50 GeV, is set on the GGM gluino mass, while a lower limit of 1/R > 961 GeV is set on the UED compactification radius R. These limits provide the most stringent tests of these models to date.

  • 355. Aad, G.
    et al.
    Grahn, Karl-Johan
    DESY, D-2000 Hamburg, Germany .
    Lund-Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    Lafaye, Remi
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    et, al
    Search for heavy long-lived charged particles with the ATLAS detector in pp collisions at root s=7 TeV2011In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 703, no 4, p. 428-446Article in journal (Refereed)
    Abstract [en]

    A search for long-lived charged particles reaching the muon spectrometer is performed using a data sample of 37 pb(-1) from pp collisions at root s = 7 TeV collected by the ATLAS detector at the LHC in 2010. No excess is observed above the estimated background. Stable (tau) over bar sleptons are excluded at 95% CL up to a mass of 136 GeV, in GMSB models with N(5) = 3 , m(messenger) = 250 TeV, sign(mu) = 1 and tan beta = 5. Electroweak production of sleptons is excluded up to a mass of 110 GeV. Gluino R-hadrons in a generic interaction model are excluded up to masses of 530 GeV to 544 GeV depending on the fraction of R-hadrons produced as (g) over bar -balls.

  • 356. Aad, G.
    et al.
    Grahn, Karl-Johan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Lund-Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    University of Chicago.
    Zwalinski, L.
    Lafaye, Remi
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    et, al
    Search for high mass dilepton resonances in pp collisions at root s=7 TeV with the ATLAS experiment2011In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 700, no 3-4, p. 163-180Article in journal (Refereed)
    Abstract [en]

    This Letter presents a search for high mass e(+)e(-) or mu(+)mu(-) resonances in pp collisions at root s = 7 TeV at the LHC. The data were recorded by the ATLAS experiment during 2010 and correspond to a total integrated luminosity of similar to 40 pb(-1). No statistically significant excess above the Standard Model expectation is observed in the search region of dilepton invariant mass above 110 GeV. Upper limits at the 95% confidence level are set on the cross section times branching ratio of Z' resonances decaying to dielectrons and dimuons as a function of the resonance mass. A lower mass limit of 1.048 TeV on the Sequential Standard Model Z' boson is derived, as well as mass limits on Z* and E(6)-motivated Z' models.

  • 357. Aad, G.
    et al.
    Grahn, Karl-Johan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Lund-Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    University of Chicago.
    Zwalinski, L.
    Lafaye, Remi
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    et, al
    Search for high-mass states with one lepton plus missing transverse momentum in proton-proton collisions root s=7 TeV with the ATLAS detector2011In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 701, no 1, p. 50-69Article in journal (Refereed)
    Abstract [en]

    The ATLAS detector is used to search for high-mass states, such as heavy charged gauge bosons (W'. W*), decaying to a charged lepton (electron or muon) and a neutrino. Results are presented based on the analysis of pp collisions at a center-of-mass energy of 7 TeV corresponding to an integrated luminosity of 36 pb(-1). No excess beyond standard model expectations is observed. A W' with sequential standard model couplings is excluded at 95% confidence level for masses below 1.49 TeV, and a W* (charged chiral boson) for masses below 1.35 TeV.

  • 358. Aad, G.
    et al.
    Grahn, Karl-Johan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Lund-Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    University of Chicago.
    Zwalinski, L.
    Lafaye, Remi
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    et, al
    Search for massive long-lived highly ionising particles with the ATLAS detector at the LHC2011In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 698, no 5, p. 353-370Article in journal (Refereed)
    Abstract [en]

    A search is made for massive highly ionising particles with lifetimes in excess of 100 ns, with the ATLAS experiment at the Large Hadron Collider, using 3.1 pb(-1) of pp collision data taken at root s = 7 TeV. The signature of energy loss in the ATLAS inner detector and electromagnetic calorimeter is used. No such particles are found and limits on the production cross section for electric charges 6e <= vertical bar q vertical bar <= 17e and masses 200 GeV <= m <= 1000 GeV are set in the range 1-12 pb for different hypotheses on the production mechanism.

  • 359. Aad, G.
    et al.
    Grahn, Karl-Johan
    DESY, D-2000 Hamburg, Germany .
    Lund-Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    Lafaye, Remi
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    et, al
    Search for neutral MSSM Higgs bosons decaying to tau(+)tau(-) pairs in proton-proton collisions root s=7 TeV with the ATLAS detector2011In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 705, no 3, p. 174-192Article in journal (Refereed)
    Abstract [en]

    A search for neutral Higgs bosons decaying to pairs of tau leptons with the ATLAS detector at the LHC is presented. The analysis is based on proton-proton collisions at a center-of-mass energy of 7 TeV, recorded in 2010 and corresponding to an integrated luminosity of 36 pb(-1). After signal selection, 276 events are observed in this data sample. The observed number of events is consistent with the total expected background of 269 +/- 36 events. Exclusion limits at the 95% confidence level are derived for the production cross section of a generic Higgs boson phi as a function of the Higgs boson mass and for A/H/h production in the Minimal Supersymmetric Standard Model (MSSM) as a function of the parameters m(A) and tan beta.

  • 360. Aad, G.
    et al.
    Grahn, Karl-Johan
    DESY, D-2000 Hamburg, Germany .
    Lund-Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    Lafaye, Remi
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    et, al
    Search for pair production of first or second generation leptoquarks in proton-proton collisions at root s=7 TeV using the ATLAS detector at the LHC2011In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 83, no 11, p. 112006-Article in journal (Refereed)
    Abstract [en]

    This paper describes searches for the pair production of first or second generation scalar leptoquarks using 35 pb(-1) of proton-proton collision data recorded by the ATLAS detector at root s = 7 TeV. Leptoquarks are searched in events with two oppositely-charged muons or electrons and at least two jets, and in events with one muon or electron, missing transverse momentum and at least two jets. After event selection, the observed yields are consistent with the predicted backgrounds. Leptoquark production is excluded at the 95% CL for masses M-LQ < 376 (319) GeV and M-LQ < 422 (362) GeV for first and second generation scalar leptoquarks, respectively, when assuming the branching fraction of a leptoquark to a charged lepton is equal to 1.0 (0.5).

  • 361. Aad, G.
    et al.
    Grahn, Karl-Johan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Lund-Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    University of Chicago.
    Zwalinski, L.
    Lafaye, Remi
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    et, al
    Search for squarks and gluinos using final states with jets and missing transverse momentum with the ATLAS detector in root s=7 TeV proton-proton collisions2011In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 701, no 2, p. 186-203Article in journal (Refereed)
    Abstract [en]

    A search for squarks and gluinos in final states containing jets, missing transverse momentum and no electrons or muons is presented. The data were recorded by the ATLAS experiment in root s = 7 TeV proton-proton collisions at the Large Hadron Collider. No excess above the Standard Model background expectation was observed in 35 pb(-1) of analysed data. Gluino masses below 500 GeV are excluded at the 95% confidence level in simplified models containing only squarks of the first two generations, a gluino octet and a massless neutralino. The exclusion increases to 870 GeV for equal mass squarks and gluinos. In MSUGRA/CMSSM models with tan beta = 3, A(0) = 0 and mu > 0, squarks and gluinos of equal mass are excluded below 775 GeV. These are the most stringent limits to date.

  • 362. Aad, G.
    et al.
    Grahn, Karl-Johan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Lund-Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    University of Chicago.
    Zwalinski, L.
    Lafaye, Remi
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    et, al
    Search for stable hadronising squarks and gluinos with the ATLAS experiment at the LHC2011In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 701, no 1, p. 1-19Article in journal (Refereed)
    Abstract [en]

    Hitherto unobserved long-lived massive particles with electric and/or colour charge are predicted by a range of theories which extend the Standard Model. In this Letter a search is performed at the ATLAS experiment for slow-moving charged particles produced in proton-proton collisions at 7 TeV centre-of-mass energy at the LHC, using a data-set corresponding to an integrated luminosity of 34 pb(-1). No deviations from Standard Model expectations are found. This result is interpreted in a framework of supersymmetry models in which coloured sparticles can hadronise into long-lived bound hadronic states, termed R-hadrons, and 95% CL limits are set on the production cross-sections of squarks and gluinos. The influence of R-hadron interactions in matter was studied using a number of different models, and lower mass limits for stable sbottoms and stops are found to be 294 and 309 GeV respectively. The lower mass limit for a stable gluino lies in the range from 562 to 586 GeV depending on the model assumed. Each of these constraints is the most stringent to date.

  • 363. Aad, G.
    et al.
    Grahn, Karl-Johan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Lund-Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    University of Chicago.
    Zwalinski, L.
    Lafaye, Remi
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    et, al
    Search for supersymmetric particles in events with lepton pairs and large missing transverse momentum in root s=7 TeV proton-proton collisions with the ATLAS experiment2011In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 71, no 7, p. 1682-Article in journal (Refereed)
    Abstract [en]

    Results are presented of searches for the production of supersymmetric particles decaying into final states with missing transverse momentum and exactly two isolated leptons in root s = 7 TeV proton-proton collisions at the Large Hadron Collider. Search strategies requiring lepton pairs with identical-sign or opposite-sign electric charges are described. In a data sample corresponding to an integrated luminosity of 35 pb(-1) collected with the ATLAS detector, no significant excesses are observed. Based on specific benchmark models, limits are placed on the squark mass between 450 and 690 GeV for squarks approximately degenerate in mass with gluinos, depending on the supersymmetric mass hierarchy considered.

  • 364. Aad, G.
    et al.
    Grahn, Karl-Johan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Lund-Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    University of Chicago.
    Zwalinski, L.
    Lafaye, Remi
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    et, al
    Search for supersymmetry in pp collisions at root s=7 TeV in final states with missing transverse momentum and b-jets2011In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 701, no 4, p. 398-416Article in journal (Refereed)
    Abstract [en]

    Results are presented of a search for supersymmetric particles in events with large missing transverse momentum and at least one heavy flavour jet candidate in root s = 7 TeV proton proton collisions. In a data sample corresponding to an integrated luminosity of 35 pb(-1) recorded by the ATLAS experiment at the Large Hadron Collider, no significant excess is observed with respect to the prediction for Standard Model processes. For R-parity conserving models in which sbottoms (stops) are the only squarks to appear in the gluino decay cascade, gluino masses below 590 GeV (520 GeV) are excluded at the 95% C.L. The results are also interpreted in an MSUGRA/CMSSM supersymmetry breaking scenario with tan beta = 40 and in an SO(10) model framework.

  • 365. Aad, G.
    et al.
    Grahn, Karl-Johan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Lund-Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    University of Chicago.
    Zwalinski, L.
    Lafaye, Remi
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    et, al
    Search for Supersymmetry Using Final States with One Lepton, Jets, and Missing Transverse Momentum with the ATLAS Detector in root s=7 TeV pp Collisions2011In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 106, no 13, p. 131802-1-131802-19Article in journal (Refereed)
    Abstract [en]

    This Letter presents the first search for supersymmetry in final states containing one isolated electron or muon, jets, and missing transverse momentum from root s = 7 TeV proton-proton collisions at the LHC. The data were recorded by the ATLAS experiment during 2010 and correspond to a total integrated luminosity of 35 pb(-1). No excess above the standard model background expectation is observed. Limits are set on the parameters of the minimal supergravity framework, extending previous limits. Within this framework, for A(0) = 0 GeV, tan beta = 3, and mu > 0 and for equal squark and gluino masses, gluino masses below 700 GeV are excluded at 95% confidence level.

  • 366. Aad, G.
    et al.
    Grahn, Karl-Johan
    DESY, D-2000 Hamburg, Germany .
    Lund-Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    University of Chicago.
    Zwalinski, L.
    Lafaye, Remi
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    et, al
    Search for the Standard Model Higgs boson in the decay channel H -> ZZ(()*()) -> 4l with the ATLAS detector2011In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 705, no 5, p. 435-451Article in journal (Refereed)
    Abstract [en]

    A search for the Standard Model Higgs boson in the decay channel H -> ZZ(()*()) l(+)l(-)l'l'(-), where l = e, mu, is presented. Proton-proton collision data at root s = 7 TeV recorded with the ATLAS detector and corresponding to an average integrated luminosity of 2.1 fb(-1) are compared to the Standard Model expectations. Upper limits on the production cross section of a Standard Model Higgs boson with a mass between 110 and 600 GeV are derived. The observed (expected) 95% confidence level upper limit on the production cross section for a Higgs boson with a mass of 194 GeV, the region with the best expected sensitivity for this search, is 0.99 (1.01) times the Standard Model prediction. The Standard Model Higgs boson is excluded at 95% confidence level in the mass ranges 191-197, 199-200 and 214-224 GeV.

  • 367. Aad, G.
    et al.
    Grahn, Karl-Johan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Lund-Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    University of Chicago.
    Zwalinski, L.
    Lafaye, Remi
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    et, al
    Study of jet shapes in inclusive jet production in pp collisions at root s=7 TeV using the ATLAS detector2011In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 83, no 5, p. 052003-Article in journal (Refereed)
    Abstract [en]

    Jet shapes have been measured in inclusive jet production in proton-proton collisions at root s = 7 TeV using 3 pb(-1) of data recorded by the ATLAS experiment at the LHC. Jets are reconstructed using the anti-k(t) algorithm with transverse momentum 30 GeV < p(T) < 600 GeV and rapidity in the region vertical bar y vertical bar < 2.8. The data are corrected for detector effects and compared to several leading-order QCD matrix elements plus parton shower Monte Carlo predictions, including different sets of parameters tuned to model fragmentation processes and underlying event contributions in the final state. The measured jets become narrower with increasing jet transverse momentum and the jet shapes present a moderate jet rapidity dependence. Within QCD, the data test a variety of perturbative and nonperturbative effects. In particular, the data show sensitivity to the details of the parton shower, fragmentation, and underlying event models in the Monte Carlo generators. For an appropriate choice of the parameters used in these models, the data are well described.

  • 368. Aad, G.
    et al.
    Grahn, Karl-Johan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Lund-Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    University of Chicago.
    Zychacek, V.
    Lafaye, Remi
    Univ Savoie, LAPP, CNTS IN2P3, Annecy Le Vieux, France.
    et, al
    The ATLAS Experiment at the CERN Large Hadron Collider2008In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 3, p. S08003-Article in journal (Refereed)
    Abstract [en]

    The ATLAS detector as installed in its experimental cavern at point 1 at CERN is described in this paper. A brief overview of the expected performance of the detector when the Large Hadron Collider begins operation is also presented.

  • 369. Aad, G.
    et al.
    Grahn, Karl-Johan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Lund-Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    zur Nedden, M.
    et al.,
    The ATLAS Collaboration2009In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 830, no 1-4, p. 925c-940cArticle in journal (Refereed)
  • 370.
    Aad, G.
    et al.
    Aix Marseille Univ, CPPM, Marseille, France.;CNRS, IN2P3, Marseille, France..
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Dept Phys, S-10044 Stockholm, Sweden..
    Morley, Anthony
    KTH, School of Engineering Sciences (SCI), Physics. Royal Inst Technol, Dept Phys, S-10044 Stockholm, Sweden..
    Sidebo, P. Edvin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Dept Phys, S-10044 Stockholm, Sweden..
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Dept Phys, S-10044 Stockholm, Sweden..
    Zwalinski, L.
    CERN, Geneva, Switzerland..
    et al,
    Erratum to: Study of the spin and parity of the Higgs boson in diboson decays with the ATLAS detector2016In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 76, no 3, article id 152Article in journal (Refereed)
  • 371.
    Aad, G.
    et al.
    Aix Marseille Univ, CPPM, CNRS, IN2P3, Marseille, France..
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ohm, Christian
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ripellino, Giulia
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Sidebo, P. Edvin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    CERN, Geneva, Switzerland..
    Measurement of distributions sensitive to the underlying event in inclusive Z boson production in pp collisions at root s=13 TeV with the ATLAS detector2019In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 79, no 8, article id 666Article in journal (Refereed)
    Abstract [en]

    This paper presents measurements of charged-particle distributions sensitive to the properties of the underlying event in events containing a Z boson decaying into a muon pair. The data were obtained using the ATLAS detector at the LHC in proton-proton collisions at a centre-of-mass energy of 13 TeV with an integrated luminosity of 3.2 fb(-1). Distributions of the charged-particle multiplicity and of the charged-particle transverse momentum are measured in regions of the azimuth defined relative to the Z boson direction. The measured distributions are compared with the predictions of various Monte Carlo generators which implement different underyling event models. The Monte Carlo model predictions qualitatively describe the data well, but with some significant discrepancies.

  • 372.
    Aad, G.
    et al.
    Aix Marseille Univ, CPPM, CNRS, IN2P3, Marseille, France..
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ohm, Christian
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ripellino, Giulia
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Sidebo, P. Edvin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    CERN, Geneva, Switzerland..
    Search for electroweak diboson production in association with a high-mass dijet system in semileptonic final states in pp collisions at root s=13 TeV with the ATLAS detector2019In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 100, no 3, article id 032007Article in journal (Refereed)
    Abstract [en]

    This paper reports on a search for electroweak diboson (WW/WZ/ZZ) production in association with a high-mass dijet system, using data from proton-proton collisions at a center-of-mass energy of N root s = 13 TeV. The data, corresponding to an integrated luminosity of 35.5 fb(-1), were recorded with the ATLAS detector in 2015 and 2016 at the Large Hadron Collider. The search is performed in final states in which one boson decays leptonically, and the other boson decays hadronically. The hadronically decaying W/Z boson is reconstructed as either two small-radius jets or one large-radius jet using jet substructure techniques. The electroweak production of WW/WZ/ZZ in association with two jets is measured with an observed (expected) significance of 2.7 (2.5) standard deviations, and the fiducial cross section is measured to be 45.1 +/- 8.6(stat.)(-14.6)(+15.9)(syst.) fb.

  • 373.
    Aad, G.
    et al.
    Aix Marseille Univ, IN2P3, CNRS, CPPM, Marseille, France..
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ohm, Christian
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ripellino, Giulia
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Sidebo, P. Edvin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    CERN, Geneva, Switzerland..
    et al.,
    Evidence for the production of three massive vector bosons with the ATLAS detector2019In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 798, article id UNSP 134913Article in journal (Refereed)
    Abstract [en]

    A search for the production of three massive vector bosons in proton-proton collisions is performed using data at root s = 13 TeV recorded with the ATLAS detector at the Large Hadron Collider in the years 2015-2017, corresponding to an integrated luminosity of 79.8 fb(-1). Events with two same-sign leptons l (electrons or muons) and at least two reconstructed jets are selected to search for WWW -> l nu l nu qq. Events with three leptons without any same-flavour opposite-sign lepton pairs are used to search for WWW > l nu l nu l nu, while events with three leptons and at least one same-flavour opposite-sign lepton pair and one or more reconstructed jets are used to search for WWZ -> l nu qqll. Finally, events with four leptons are analysed to search for WWZ > l nu l nu ll and WZZ > qqllll. Evidence for the joint production of three massive vector bosons is observed with a significance of 4.1 standard deviations, where the expectation is 3.1 standard deviations.

  • 374.
    Aad, G.
    et al.
    Aix Marseille Univ, CNRS, CPPM, IN2P3, Marseille, France..
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ohm, Christian
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ripellino, Giulia
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Sidebo, P. Edvin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    CERN, Geneva, Switzerland..
    et al.,
    Identification of boosted Higgs bosons decaying into b-quark pairs with the ATLAS detector at 13 TeV2019In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 79, no 10, article id 836Article in journal (Refereed)
    Abstract [en]

    This paper describes a study of techniques for identifying Higgs bosons at high transverse momenta decaying into bottom-quark pairs, H -> b (b) over bar, for proton-proton collision data collected by the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy root s = 13 TeV. These decays are reconstructed from calorimeter jets found with the anti-k(t) R = 1.0 jet algorithm. To tag Higgs bosons, a combination of requirements is used: b-tagging of R = 0.2 track-jets matched to the large-R calorimeter jet, and requirements on the jet mass and other jet substructure variables. The Higgs boson tagging efficiency and corresponding multijet and hadronic top-quark background rejections are evaluated using Monte Carlo simulation. Several benchmark tagging selections are defined for different signal efficiency targets. The modelling of the relevant input distributions used to tag Higgs bosons is studied in 36 fb(-1) of data collected in 2015 and 2016 using g -> b (b) over bar and Z(-> b (b) over bar)gamma event selections in data. Both processes are found to be well modelled within the statistical and systematic uncertainties.

  • 375.
    Aad, G.
    et al.
    Aix Marseille Univ, CPPM, CNRS, IN2P3, Marseille, France..
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ohm, Christian
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ripellino, Giulia
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Sidebo, P. Edvin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    CERN, Geneva, Switzerland..
    et al.,
    Measurement of the cross-section and charge asymmetry of W bosons produced in proton-proton collisions at root s=8 TeV with the ATLAS detector2019In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 79, no 9, article id 760Article in journal (Refereed)
    Abstract [en]

    This paper presents measurements of the W+->mu+nu and W-->mu-nu cross-sections and the associated charge asymmetry as a function of the absolute pseudorapidity of the decay muon. The data were collected in proton-proton collisions at a centre-of-mass energy of 8 TeV with the ATLAS experiment at the LHC and correspond to a total integrated luminosity of 20.2fb(-1). The precision of the cross-section measurements varies between 0.8 and 1.5% as a function of the pseudorapidity, excluding the 1.9% uncertainty on the integrated luminosity. The charge asymmetry is measured with an uncertainty between 0.002 and 0.003. The results are compared with predictions based on next-to-next-to-leading-order calculations with various parton distribution functions and have the sensitivity to discriminate between them.

  • 376.
    Aad, G.
    et al.
    Aix Marseille Univ, CPPM, CNRS, IN2P3, Marseille, France..
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ohm, Christian
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ripellino, Giulia
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Sidebo, P. Edvin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    CERN, Geneva, Switzerland..
    et al.,
    Measurement of the inclusive cross-section for the production of jets in association with a Z boson in proton-proton collisions at 8 TeV using the ATLAS detector2019In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 79, no 10, article id 847Article in journal (Refereed)
    Abstract [en]

    The inclusive cross-section for jet production in association with a Z boson decaying into an electronpositron pair is measured as a function of the transverse momentum and the absolute rapidity of jets using 19.9 fb(-1) of root s = 8 TeV proton-proton collision data collected with the ATLAS detector at the Large Hadron Collider. The measured Z + jets cross-section is unfolded to the particle level. The cross-section is compared with state-of-the-art Standard Model calculations, including the next-to-leading-order and next-to-next-to-leading-order perturbative QCD calculations, corrected for non-perturbative and QED radiation effects. The results of the measurements cover final-state jets with transverse momenta up to 1 TeV, and show good agreement with fixed-order calculations.

  • 377.
    Aad, G.
    et al.
    Aix Marseille Univ, CPPM, CNRS, IN2P3, Marseille, France..
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ohm, Christian
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ripellino, Giulia
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Sidebo, P. Edvin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    CERN, Geneva, Switzerland..
    et al.,
    Resolution of the ATLAS muon spectrometer monitored drift tubes in LHC Run 22019In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 14, article id P09011Article in journal (Refereed)
    Abstract [en]

    The momentum measurement capability of the ATLAS muon spectrometer relies fundamentally on the intrinsic single-hit spatial resolution of the monitored drift tube precision tracking chambers. Optimal resolution is achieved with a dedicated calibration program that addresses the specific operating conditions of the 354 000 high-pressure drift tubes in the spectrometer. The calibrations consist of a set of timing offsets and drift time to drift distance transfer relations, and result in chamber resolution functions. This paper describes novel algorithms to obtain precision calibrations from data collected by ATLAS in LHC Run 2 and from a gas monitoring chamber, deployed in a dedicated gas facility. The algorithm output consists of a pair of correction constants per chamber which are applied to baseline calibrations, and determined to be valid for the entire ATLAS Run 2. The final single-hit spatial resolution, averaged over 1172 monitored drift tube chambers, is 81.7 +/- 2.2 mu m.

  • 378.
    Aad, G.
    et al.
    Aix Marseille Univ, CPPM, CNRS, IN2P3, Marseille, France..
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ohm, Christian
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ripellino, Giulia
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Sidebo, P. Edvin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    CERN, Geneva, Switzerland..
    et al.,
    Search for a heavy charged boson in events with a charged lepton and missing transverse momentum from pp collisions at root s=13 TeV with the ATLAS detector2019In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 100, no 5, article id 052013Article in journal (Refereed)
    Abstract [en]

    A search for a heavy charged-boson resonance decaying into a charged lepton (electron or muon) and a neutrino is reported. A data sample of 139 fb(-1) of proton-proton collisions at root s = 13 TeV collected with the ATLAS detector at the LHC during 2015-2018 is used in the search. The observed transverse mass distribution computed from the lepton and missing transverse momenta is consistent with the distribution expected from the Standard Model, and upper limits on the cross section for pp -> W'-> lv are extracted (l = e or mu). These vary between 1.3 pb and 0.05 tb depending on the resonance mass in the range between 0.15 and 7.0 TeV at 95% confidence level for the electron and muon channels combined. Gauge bosons with a mass below 6.0 and 5.1 TeV are excluded in the electron and muon channels, respectively, in a model with a resonance that has couplings to fermions identical to those of the Standard Model W boson. Cross-section limits are also provided for resonances with several fixed Gamma/m values in the range between 1% and 15%. Model-independent limits are derived in single-bin signal regions defined by a varying minimum transverse mass threshold. The resulting visible cross-section upper limits range between 4.6 (15) ph and 22 (22) ab as the threshold increases from 130 (110) GeV to 5.1 (5.1) TeV in the electron (muon) channel.

  • 379.
    Aad, G.
    et al.
    Aix Marseille Univ, CPPM, CNRS, IN2P3, Marseille, France..
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ohm, Christian
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ripellino, Giulia
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Sidebo, P. Edvin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    CERN, Geneva, Switzerland..
    et al.,
    Search for high-mass dilepton resonances using 139 fb(-1) of pp collision data collected at root s=13 TeV with the ATLAS detector2019In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 796, p. 68-87Article in journal (Refereed)
    Abstract [en]

    A search for high-mass dielectron and dimuon resonances in the mass range of 250 GeV to 6TeV is presented. The data were recorded by the ATLAS experiment in proton-proton collisions at a centre-ofmass energy of root s = 13 TeV during Run 2 of the Large Hadron Collider and correspond to an integrated luminosity of 139 fb(-1). A functional form is fitted to the dilepton invariant-mass distribution to model the contribution from background processes, and a generic signal shape is used to determine the significance of observed deviations from this background estimate. No significant deviation is observed and upper limits are placed at the 95% confidence level on the fiducial cross-section times branching ratio for various resonance width hypotheses. The derived limits are shown to be applicable to spin-0, spin-1 and spin-2 signal hypotheses. For a set of benchmark models, the limits are converted into lower limits on the resonance mass and reach 4.5 TeV for the E-6-motivated Z(psi)' boson. Also presented are limits on Heavy Vector Triplet model couplings.

  • 380.
    Aad, G.
    et al.
    Aix Marseille Univ, CPPM, Marseille, France.;CNRS, IN2P3, Marseille, France..
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Phys Dept, Stockholm, Sweden..
    Sidebo, P. Edvin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Phys Dept, Stockholm, Sweden..
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Phys Dept, Stockholm, Sweden..
    Woods, N.
    Univ Wisconsin Madison, Madison, WI USA..
    Measurements of the Higgs boson production and decay rates and constraints on its couplings from a combined ATLAS and CMS analysis of the LHC pp collision data at root s=7 and 8 TeV2016In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 8, article id 045Article in journal (Refereed)
    Abstract [en]

    Combined ATLAS and CMS measurements of the Higgs boson production and decay rates, as well as constraints on its couplings to vector bosons and fermions, are presented. The combination is based on the analysis of five production processes, namely gluon fusion, vector boson fusion, and associated production with a W or a Z boson or a pair of top quarks, and of the six decay modes H -> ZZ; WW, gamma gamma; tau tau; bb, and mu mu. All results are reported assuming a value of 125: 09 GeV for the Higgs boson mass, the result of the combined measurement by the ATLAS and CMS experiments. The analysis uses the CERN LHC proton-proton collision data recorded by the ATLAS and CMS experiments in 2011 and 2012, corresponding to integrated luminosities per experiment of approximately 5 fb(-1) at root s = 7TeV and 20 fb(-1) at root s = 8TeV. The Higgs boson production and decay rates measured by the two experiments are combined within the context of three generic parameterisations: two based on cross sections and branching fractions, and one on ratios of coupling modifiers. Several interpretations of the measurements with more model-dependent parameterisations are also given. The combined signal yield relative to the Standard Model prediction is measured to be 1.09 +/- 0.11. The combined measurements lead to observed significances for the vector boson fusion production process and for the H -> tau tau decay of 5.4 and 5.5 standard deviations, respectively. The data are consistent with the Standard Model predictions for all parameterisations considered.

  • 381.
    Aad, G.
    et al.
    Aix Marseille Univ, CPPM, Marseille, France.;CNRS, IN2P3, Marseille, France..
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Phys Dept, Stockholm, Sweden..
    Sidebo, P. Edvin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Phys Dept, Stockholm, Sweden..
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Phys Dept, Stockholm, Sweden..
    Zwalinski, L.
    CERN, Geneva, Switzerland..
    Search for supersymmetry at root s=13 TeV in final states with jets and two same-sign leptons or three leptons with the ATLAS detector2016In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 76, no 5, article id 259Article in journal (Refereed)
    Abstract [en]

    A search for strongly produced supersymmetric particles is conducted using signatures involving multiple energetic jets and either two isolated leptons (e or mu) with the same electric charge or at least three isolated leptons. The search also utilises b-tagged jets, missing transverse momentum and other observables to extend its sensitivity. The analysis uses a data sample of proton-proton collisions at root s = 13 TeV recorded with the ATLAS detector at the Large Hadron Collider in 2015 corresponding to a total integrated luminosity of 3.2 fb(-1). No significant excess over the Standard Model expectation is observed. The results are interpreted in several simplified supersymmetric models and extend the exclusion limits from previous searches. In the context of exclusive production and simplified decay modes, gluino masses are excluded at 95% confidence level up to 1.1-1.3 TeV for light neutralinos (depending on the decay channel), and bottom squark masses are also excluded up to 540 GeV. In the former scenarios, neutralino masses are also excluded up to 550-850 GeV for gluino masses around 1 TeV.

  • 382.
    Aad, G.
    et al.
    Aix Marseille Univ, CPPM, Marseille, France.;CNRS IN2P3, Marseille, France..
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Phys Dept, Stockholm, Sweden..
    Sidebo, P. Edvin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Phys Dept, Stockholm, Sweden..
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Phys Dept, Stockholm, Sweden..
    Zwalinski, L.
    CERN, Geneva, Switzerland..
    et al,
    A new method to distinguish hadronically decaying boosted Z bosons from W bosons using the ATLAS detector2016In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 76, no 5, article id 238Article in journal (Refereed)
    Abstract [en]

    The distribution of particles inside hadronic jets produced in the decay of boosted W and Z bosons can be used to discriminate such jets from the continuum background. Given that a jet has been identified as likely resulting from the hadronic decay of a boosted W or Z boson, this paper presents a technique for further differentiating Z bosons from W bosons. The variables used are jet mass, jet charge, and a b-tagging discriminant. A likelihood tagger is constructed from these variables and tested in the simulation of W' -> WZ for bosons in the transverse momentum range 200 GeV < p(T) < 400 GeV in root s = 8 TeV pp collisions with the ATLAS detector at the LHC. For Z-boson tagging efficiencies of epsilon(Z) = 90, 50, and 10 %, one can achieve W+-boson tagging rejection factors (1/epsilon(W+)) of 1.7, 8.3 and 1000, respectively. It is not possible to measure these efficiencies in the data due to the lack of a pure sample of high p(T), hadronically decaying Z bosons. However, the modelling of the tagger inputs for boosted W bosons is studied in data using a t (t) over bar -enriched sample of events in 20.3 fb(-1) of data at root s = 8 TeV. The inputs are well modelled within uncertainties, which builds confidence in the expected tagger performance.

  • 383.
    Aad, G.
    et al.
    Aix Marseille Univ, CPPM, Marseille, France.;CNRS, IN2P3, Marseille, France..
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Dept Phys, S-10044 Stockholm, Sweden..
    Sidebo, P. Edvin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Dept Phys, S-10044 Stockholm, Sweden..
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Dept Phys, S-10044 Stockholm, Sweden..
    Zwalinski, L.
    CERN, CH-1211 Geneva 23, Switzerland..
    et al,
    Erratum to: ATLAS Run 1 searches for direct pair production of third-generation squarks at the Large Hadron Collider2016In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 76, no 3, article id 153Article in journal (Refereed)
  • 384.
    Aad, G.
    et al.
    Aix Marseille Univ, CPPM, Marseille, France.;CNRS, IN2P3, Marseille, France..
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Dept Phys, Stockholm, Sweden..
    Sidebo, P. Edvin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Dept Phys, Stockholm, Sweden..
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Dept Phys, Stockholm, Sweden..
    Zwalinski, L.
    CERN, CH-1211 Geneva 23, Switzerland..
    et al,
    Measurement of the charged-particle multiplicity inside jets from root s=8 TeV pp collisions with the ATLAS detector2016In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 76, no 6, article id 322Article in journal (Refereed)
    Abstract [en]

    The number of charged particles inside jets is a widely used discriminant for identifying the quark or gluon nature of the initiating parton and is sensitive to both the perturbative and non-perturbative components of fragmentation. This paper presents a measurement of the average number of charged particles with p(T) > 500 MeV inside high-momentum jets in dijet events using 20.3 fb(-1) of data recorded with the ATLAS detector in pp collisions at root s = 8 TeV collisions at the LHC. The jets considered have transverse momenta from 50 GeV up to and beyond 1.5 TeV. The reconstructed charged-particle track multiplicity distribution is unfolded to remove distortions from detector effects and the resulting charged-particle multiplicity is compared to several models. Furthermore, quark and gluon jet fractions are used to extract the average charged-particle multiplicity for quark and gluon jets separately.

  • 385.
    Aad, G.
    et al.
    Aix Marseille Univ, CPPM, Marseille, France.;CNRS, IN2P3, Marseille, France..
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Dept Phys, Stockholm, Sweden..
    Sidebo, P. Edvin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Dept Phys, Stockholm, Sweden..
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Dept Phys, Stockholm, Sweden..
    Zwalinski, L.
    CERN, Geneva, Switzerland..
    et al,
    Measurement of the CP-violating phase phi(s) and the B-s(0) meson decay width difference with B-s(0) -> J/psi phi decays in ATLAS2016In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 8, article id 147Article in journal (Refereed)
    Abstract [en]

    A measurement of the B-s(0) decay parameters in the B-s(0) -> J/psi/phi channel using an integrated luminosity of 14.3 fb(-1) collected by the ATLAS detector from 8TeV pp collisions at the LHC is presented. The measured parameters include the CP-violating phase phi(s), the decay width Gamma(s) and the width di ff erence between the mass eigenstates Delta Gamma(s). The values measured for the physical parameters are statistically combined with those from 4.9 fb-1 of 7TeV data, leading to the following: phi(s) = -0.090 +/- 0.078 (stat.) +/- 0.041 (syst.) rad Delta Gamma s = 0.085 +/- 0.011 (stat.) +/- 0.007 (syst.) ps(-1) Gamma(s) = 0.675 +/- 0.003 (stat.) +/- 0.003 (syst:) ps(-1). In the analysis the parameter Delta Gamma(s) is constrained to be positive. Results for phi(s) and Delta Gamma(s) are also presented as 68% and 95% likelihood contours in the phi(s)-Delta Gamma(s) plane. Also measured in this decay channel are the transversity amplitudes and corresponding strong phases. All measurements are in agreement with the Standard Model predictions.

  • 386. Aad, G
    et al.
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Sidebo, Edvin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L
    et al.,
    A search for prompt lepton-jets in pp collisions at root s=8 TeV with the ATLAS detector2016In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 2, article id 062Article in journal (Refereed)
    Abstract [en]

    A search is presented for a new, light boson with a mass of about 1 GeV and decaying promptly to jets of collimated electrons and/or muons (lepton-jets). The analysis is performed with 20.3 fb(-1) of data collected by the ATLAS detector at the Large Hadron Collider in proton-proton collisions at a centre-of-mass energy of 8 TeV. Events are required to contain at least two lepton-jets. This study finds no statistically significant deviation from predictions of the Standard Model and places 95% confidence-level upper limits on the contribution of new phenomena beyond the SM, incuding SUSY-portal and Higgs-portal models, on the number of events with lepton-jets.

  • 387. Aad, G
    et al.
    Jovicevic, J
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Kuwertz, E S
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Lund-Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Morley, Anthony
    KTH, School of Engineering Sciences (SCI), Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    Centrality and rapidity dependence of inclusive jet production in root(NN)-N-S=5.02 TeV proton-lead collisions with the ATLAS detector2015In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 748, p. 392-413Article in journal (Refereed)
    Abstract [en]

    Measurements of the centrality and rapidity dependence of inclusive jet production in root(NN)-N-S = 5.02 TeV proton-lead (p + Pb) collisions and the jet cross-section in root s = 2.76 TeV proton-proton collisions are presented. These quantities are measured in datasets corresponding to an integrated luminosity of 27.8 nb(-1) and 4.0 pb(-1), respectively, recorded with the ATLAS detector at the Large Hadron Collider in 2013. The p + Pb collision centrality was characterised using the total transverse energy measured in the pseudorapidity interval -4.9 < eta < -3.2 in the direction of the lead beam. Results are presented for the double-differential per-collision yields as a function of jet rapidity and transverse momentum (p(T)) for minimum-bias and centrality-selected p + Pb collisions, and are compared to the jet rate from the geometric expectation. The total jet yield in minimum-bias events is slightly enhanced above the expectation in a p(T)-dependent manner but is consistent with the expectation within uncertainties. The ratios of jet spectra from different centrality selections show a strong modification of jet production at all p(T) at forward rapidities and for large pT at mid-rapidity, which manifests as a suppression of the jet yield in central events and an enhancement in peripheral events. These effects imply that the factorisation between hard and soft processes is violated at an unexpected level in proton-nucleus collisions. Furthermore, the modifications at forward rapidities are found to be a function of the total jet energy only, implying that the violations may have a simple dependence on the hard parton-parton kinematics. (C) 2015 CERN for the benefit of the ATLAS Collaboration. Published by Elsevier B.V.

  • 388. Aad, G.
    et al.
    Jovicevic, Jelena
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Kuwertz, Emma
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Morley, Anthony
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    et al.,
    Determination of the top-quark pole mass using t(t)over-bar+1-jet events collected with the ATLAS experiment in 7 TeV pp collisions2015In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 10, article id 121Article in journal (Refereed)
    Abstract [en]

    Simultaneous measurements of the t (t) over bar, W+W-, and Z/gamma* -> tau tau production cross-sections using an integrated luminosity of 4.6 fb(-1) of pp collisions at root s = 7 TeV collected by the ATLAS detector at the LHC are presented. Events are selected with two high transverse momentum leptons consisting of an oppositely charged electron and muon pair. The three processes are separated using the distributions of the missing transverse momentum of events with zero and greater than zero jet multiplicities. Measurements of the fiducial cross-section are presented along with results that quantify for the first time the underlying correlations in the predicted and measured cross-sections due to proton parton distribution functions. These results indicate that the correlated next-to-leading-order predictions for t (t) over bar and Z/gamma* -> tau tau underestimate the data, while those at next-to-next-to-leading-order generally describe the data well. The full cross-sections are measured to be sigma(t (t) over bar) = 181.2 +/- 2.8(-9.5)(+9.7) +/- 3.3 +/- 3.3 pb, sigma(W+W-) = 53.3 +/- 2.7(-8.0)(+7.3) +/- 1.0 +/- 0.5 pb, and sigma(Z/gamma* -> tau tau) = 1174 +/- 24(-87)(+72) +/- 21 +/- 9 pb, where the cited uncertainties are due to statistics, systematic effects, luminosity and the LHC beam energy measurement, respectively. The W+W- measurement includes the small contribution from Higgs boson decays, H -> W+W-.

  • 389. Aad, G.
    et al.
    Jovicevic, Jelena
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Kuwertz, Emma
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Morley, Anthony
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    et al.,
    Measurement of dijet cross-sections in pp collisions at 7 TeV centre-of-mass energy using the ATLAS detector2014In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 5Article in journal (Refereed)
    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.

  • 390. Aad, G.
    et al.
    Jovicevic, Jelena
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Kuwertz, Emma
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Morley, Anthony
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    et al.,
    Measurement of the parity-violating asymmetry parameter ab and the helicity amplitudes for the decay Lambda(0)(b) -> J/psi Lambda(0) with the ATLAS detector2014In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 89, no 9Article in journal (Refereed)
    Abstract [en]

    A measurement of the parity-violating decay asymmetry parameter, ab, and the helicity amplitudes for the decay.Lambda(0)(b) -> J/psi(mu(+) mu(-)) Lambda(0)(p pi(-)) is reported. The analysis is based on 1400 Lambda(0)(b)and (Lambda) over bar (0)(b) baryons selected in 4.6 fb(-1) of proton-proton collision data with a center-of-mass energy of 7 TeV recorded by the ATLAS experiment at the LHC. By combining the.0 b and. _ 0 b samples under the assumption of CP conservation, the value of ab is measured to be 0.30 +/- 0.16(stat) +/- 0.06(syst). This measurement provides a test of theoretical models based on perturbative QCD or heavy-quark effective theory.

  • 391. Aad, G.
    et al.
    Jovicevic, Jelena
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Kuwertz, Emma
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Morley, Anthony
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    et al.,
    Measurement of the production of a W boson in association with a charm quark in pp collisions at root s=7 TeV with the ATLAS detector2014In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 5, p. 1-67Article in journal (Refereed)
    Abstract [en]

    The production of a W boson in association with a single charm quark is studied using 4.6 fb(-1) of pp collision data at root s = 7 TeV collected with the ATLAS detector at the Large Hadron Collider. In events in which a W boson decays to an electron or muon, the charm quark is tagged either by its semileptonic decay to a muon or by the presence of a charmed meson. The integrated and differential cross sections as a function of the pseudorapidity of the lepton from the W-boson decay are measured. Results are compared to the predictions of next-to-leading-order QCD calculations obtained from various parton distribution function parameterisations. The ratio of the strange-to-down sea-quark distributions is determined to be 0.96(-0.30)(+0.26) at Q (2) = 1.9 GeV2, which supports the hypothesis of an SU(3)-symmetric composition of the light-quark sea. Additionally, the cross-section ratio sigma(W (+) +)/sigma(W (-) + c) is compared to the predictions obtained using parton distribution function parameterisations with different assumptions about the s-(s) over bar quark asymmetry.

  • 392. Aad, G.
    et al.
    Jovicevic, Jelena
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Kuwertz, Emma
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Morley, Anthony
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    et al.,
    Measurement of the underlying event in jet events from 7 proton-proton collisions with the ATLAS detector2014In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 74, no 8, p. 2965-Article in journal (Refereed)
    Abstract [en]

    Distributions sensitive to the underlying event in QCD jet events have been measured with the ATLAS detector at the LHC, based on of proton-proton collision data collected at a centre-of-mass energy of 7 . Charged-particle mean and densities of all-particle and charged-particle multiplicity and have been measured in regions azimuthally transverse to the hardest jet in each event. These are presented both as one-dimensional distributions and with their mean values as functions of the leading-jet transverse momentum from 20 to 800 . The correlation of charged-particle mean with charged-particle multiplicity is also studied, and the densities include the forward rapidity region; these features provide extra data constraints for Monte Carlo modelling of colour reconnection and beam-remnant effects respectively. For the first time, underlying event observables have been computed separately for inclusive jet and exclusive dijet event selections, allowing more detailed study of the interplay of multiple partonic scattering and QCD radiation contributions to the underlying event. Comparisons to the predictions of different Monte Carlo models show a need for further model tuning, but the standard approach is found to generally reproduce the features of the underlying event in both types of event selection.

  • 393. Aad, G.
    et al.
    Jovicevic, Jelena
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Kuwertz, Emma
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Morley, Anthony
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    et al.,
    Measurements of Four-Lepton Production at the Z Resonance in pp Collisions at root s=7 and 8 TeV with ATLAS2014In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 112, no 23Article in journal (Refereed)
    Abstract [en]

    Measurements of four-lepton (4l, l = e,mu) production cross sections at the Z resonance in pp collisions at the LHC with the ATLAS detector are presented. For dilepton and four-lepton invariant mass regions m (l+l)- > 5 GeV and 80 < m(4l) < 100 GeV, the measured cross sections are 76 +/- 18(stat) +/- 4(syst) +/- 1.4(lumi) fb and 107 +/- 9(stat) +/- 4(syst) +/- 3.0(lumi) fb at root s=7 and 8 TeV, respectively. By subtracting the nonresonant 4l production contributions and normalizing with Z -> mu(+)mu(-) events, the branching fraction for the Z boson decay to 4l is determined to be (3.20 +/- 0.25(stat) +/- 0.13(syst)) x10(-6), consistent with the standard model prediction.

  • 394. Aad, G.
    et al.
    Jovicevic, Jelena
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Kuwertz, Emma
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Morley, Anthony
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    et al.,
    Search for anomalous production of prompt same-sign lepton pairs and pair-produced doubly charged Higgs bosons with root s=8 TeV pp collisions using the ATLAS detector2015In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 3, article id 041Article in journal (Refereed)
    Abstract [en]

    A low-background inclusive search for new physics in events with same-sign dileptons is presented. The search uses proton-proton collisions corresponding to 20.3 fb(-1) of integrated luminosity taken in 2012 at a centre-of-mass energy of 8TeV with the ATLAS detector at the LHC. Pairs of isolated leptons with the same electric charge and large transverse momenta of the type e(+/-) e(+/-), e(+/-) mu(+/-), and mu(+/-) mu(+/-) are selected and their invariant mass distribution is examined. No excess of events above the expected level of Standard Model background is found. The results are used to set upper limits on the cross-sections for processes beyond the Standard Model. Limits are placed as a function of the dilepton invariant mass within a fiducial region corresponding to the signal event selection criteria. Exclusion limits are also derived for a specific model of doubly charged Higgs boson production.

  • 395. Aad, G.
    et al.
    Jovicevic, Jelena
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Kuwertz, Emma
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Morley, Anthony
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    et al.,
    Search for direct pair production of the top squark in all-hadronic final states in proton-proton collisions at=8 TeV with the ATLAS detector2014In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 9, no 015Article in journal (Refereed)
    Abstract [en]

    The results of a search for direct pair production of the scalar partner to the top quark using an integrated luminosity of 20.1 fb(-1) of proton-proton collision data at = 8 TeV recorded with the ATLAS detector at the LHC are reported. The top squark is assumed to decay via or , where denotes the lightest neutralino (chargino) in supersymmetric models. The search targets a fully-hadronic final state in events with four or more jets and large missing transverse momentum. No significant excess over the Standard Model background prediction is observed, and exclusion limits are reported in terms of the top squark and neutralino masses and as a function of the branching fraction of . For a branching fraction of 100%, top squark masses in the range 270-645 GeV are excluded for masses below 30 GeV. For a branching fraction of 50% to either or , and assuming the mass to be twice the mass, top squark masses in the range 250-550 GeV are excluded for masses below 60 GeV.

  • 396. Aad, G.
    et al.
    Jovicevic, Jelena
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Kuwertz, Emma
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Morley, Anthony
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    et al.,
    Search for direct production of charginos, neutralinos and sleptons in final states with two leptons and missing transverse momentum in pp collisions at root s=8TeV with the ATLAS detector2014In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 5, p. 1-52Article in journal (Refereed)
    Abstract [en]

    Searches for the electroweak production of charginos, neutralinos and sleptons in final states characterized by the presence of two leptons (electrons and muons) and missing transverse momentum are performed using 20.3 fb(-1) of proton-proton collision data at root s = 8 TeV recorded with the ATLAS experiment at the Large Hadron Collider. No significant excess beyond Standard Model expectations is observed. Limits are set on the masses of the lightest chargino, next-to-lightest neutralino and sleptons for different lightest-neutralino mass hypotheses in simplified models. Results are also interpreted in various scenarios of the phenomenological Minimal Supersymmetric Standard Model.

  • 397. Aad, G.
    et al.
    Jovicevic, Jelena
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Kuwertz, Emma
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Morley, Anthony
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    et al.,
    Search for direct top squark pair production in events with a boson, -jets and missing transverse momentum in TeV collisions with the ATLAS detector2014In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 74, no 6Article in journal (Refereed)
    Abstract [en]

    A search is presented for direct top squark pair production using events with at least two leptons including a same-flavour opposite-sign pair with invariant mass consistent with the boson mass, jets tagged as originating from -quarks and missing transverse momentum. The analysis is performed with proton-proton collision data at collected with the ATLAS detector at the LHC in 2012 corresponding to an integrated luminosity of 20.3 fb. No excess beyond the Standard Model expectation is observed. Interpretations of the results are provided in models based on the direct pair production of the heavier top squark state () followed by the decay to the lighter top squark state () via , and for pair production in natural gauge-mediated supersymmetry breaking scenarios where the neutralino () is the next-to-lightest supersymmetric particle and decays producing a boson and a gravitino () via the process.

  • 398. Aad, G.
    et al.
    Jovicevic, Jelena
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Kuwertz, Emma
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Morley, Anthony
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    et al.,
    Search for top quark decays t -> q H with H -> gamma gamma using the ATLAS detector2014In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 6, no 008Article in journal (Refereed)
    Abstract [en]

    A search is performed for flavour-changing neutral currents in the decay of a top quark to an up-type (c, u) quark and a Higgs boson, where the Higgs boson decays to two photons. The proton-proton collision data set used corresponds to 4.7 fb(-1) at root s = 7TeV and 20.3 fb(-1) at root s = 8TeV collected by the ATLAS experiment at the LHC. Top quark pair events are searched for in which one top quark decays to qH and the other decays to bW. Both the hadronic and the leptonic decay modes of the W boson are used. No significant signal is observed and an upper limit is set on the t -> qH branching ratio of 0.79% at the 95% confidence level. The corresponding limit on the tqH coupling combination root lambda(2)(tcH) + root lambda(2)(tuH) is 0.17.

  • 399. Aad, G.
    et al.
    Jovicevic, Jelena
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Kuwertz, Emma
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Morley, Anthony
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    et al.,
    Simultaneous measurements of the t(t)over-bar, W+W-, and Z/gamma* -> tau tau production cross-sections in pp collisions at root s=7 TeV with the ATLAS detector2015In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 91, no 5Article in journal (Refereed)
    Abstract [en]

    Simultaneous measurements of the t (t) over bar, W+W-, and Z/gamma* -> tau tau production cross-sections using an integrated luminosity of 4.6 fb(-1) of pp collisions at root s = 7 TeV collected by the ATLAS detector at the LHC are presented. Events are selected with two high transverse momentum leptons consisting of an oppositely charged electron and muon pair. The three processes are separated using the distributions of the missing transverse momentum of events with zero and greater than zero jet multiplicities. Measurements of the fiducial cross-section are presented along with results that quantify for the first time the underlying correlations in the predicted and measured cross-sections due to proton parton distribution functions. These results indicate that the correlated next-to-leading-order predictions for t (t) over bar and Z/gamma* -> tau tau underestimate the data, while those at next-to-next-to-leading-order generally describe the data well. The full cross-sections are measured to be sigma(t (t) over bar) = 181.2 +/- 2.8(-9.5)(+9.7) +/- 3.3 +/- 3.3 pb, sigma(W+W-) = 53.3 +/- 2.7(-8.0)(+7.3) +/- 1.0 +/- 0.5 pb, and sigma(Z/gamma* -> tau tau) = 1174 +/- 24(-87)(+72) +/- 21 +/- 9 pb, where the cited uncertainties are due to statistics, systematic effects, luminosity and the LHC beam energy measurement, respectively. The W+W- measurement includes the small contribution from Higgs boson decays, H -> W+W-.

  • 400. Aad, G.
    et al.
    Jovicevic, Jelena
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Kuwertz, Emma
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    et al.,
    Muon reconstruction efficiency and momentum resolution of the ATLAS experiment in proton-proton collisions at root s=7 TeV in 20102014In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 74, no 9, article id 3034Article in journal (Refereed)
    Abstract [en]

    This paper presents a study of the performance of the muon reconstruction in the analysis of proton–proton collisions at (Formula presented.) TeV at the LHC, recorded by the ATLAS detector in 2010. This performance is described in terms of reconstruction and isolation efficiencies and momentum resolutions for different classes of reconstructed muons. The results are obtained from an analysis of (Formula presented.) boson decays to dimuons, reconstructed from a data sample corresponding to an integrated luminosity of 40 pb(Formula presented.). The measured performance is compared to Monte Carlo predictions and deviations from the predicted performance are discussed.

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