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  • 951. Abazov, V. M.
    et al.
    Åsman, Barbro
    Clément, Christophe
    Lager, Sara
    Strandberg, Jonas
    Zylberstejn, A.
    et al.,
    Measurement of the ratio of inclusive cross sections sigma(p(p)over-bar -> Z plus b jet)/sigma(p(p)over-bar -> Z plus jet) at root s=1.96 TeV2005In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 94, no 16, p. 161801-Article in journal (Refereed)
    Abstract [en]

    Using the data collected with the D0 detector at root s=1.96 TeV, for integrated luminosities of about 180 pb(-1), we have measured the ratio of inclusive cross sections for p(p) over bar -> Z+b jet to p(p) over bar -> Z+jet production. The inclusive Z+b-jet reaction is an important background to searches for the Higgs boson in associated ZH production at the Fermilab Tevatron collider. Our measurement is the first of its kind, and relies on the Z -> e(+)e(-) and Z ->mu(+)mu(-) modes. The combined measurement of the ratio yields 0.021 +/- 0.005 for hadronic jets with transverse momenta p(T)> 20 GeV/c and pseudorapidities vertical bar eta vertical bar < 2.5, consistent with next-to-leading-order predictions of the standard model.

  • 952. Abazov, V. M.
    et al.
    Åsman, Barbro
    Clément, Christophe
    Lager, Sara
    Strandberg, Jonas
    Zylberstejn, A.
    et al.,
    Measurement of the WW production cross section in p(p)over-bar collisions at root(s)over-bar=1.96 TeV2005In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 94, no 15, p. 151801-Article in journal (Refereed)
    Abstract [en]

    We present a measurement of the W boson pair-production cross section in p(p) over bar collisions at a center-of-mass energy of root s=1.96 TeV. The data, collected with the Run II D0 detector at Fermilab, correspond to an integrated luminosity of 224-252 pb(-1) depending on the final state (ee, e mu, or mu mu). We observe 25 candidates with a background expectation of 8.1 +/- 0.6(stat)+/- 0.6(syst)+/- 0.5(lum) events. The probability for an upward fluctuation of the background to produce the observed signal is 2.3x10(-7), equivalent to 5.2 standard deviations. The measurement yields a cross section of 13.8(-3.8)(+4.3)(stat)(-0.9)(+1.2)(syst)+/- 0.9(lum) pb, in agreement with predictions from the standard model.

  • 953. Abazov, V. M.
    et al.
    Åsman, Barbro
    Clément, Christophe
    Lager, Sara
    Strandberg, Jonas
    Zylberstejn, A.
    et al.,
    Search for anomalous heavy-flavor quark production in association with W bosons2005In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 94, no 15, p. 152002-Article in journal (Refereed)
    Abstract [en]

    We search for anomalous production of heavy-flavor quark jets in association with W bosons at the Fermilab Tevatron p(p) over bar Collider in final states in which the heavy-flavor quark content is enhanced by requiring at least one tagged jet in an event. Jets are tagged using one algorithm based on semileptonic decays of b/c hadrons, and another on their lifetimes. We compare e+jets (164 pb(-1)) and mu+jets (145 pb(-1)) channels collected with the D0 detector at root s = 1.96 TeV to expectations from the standard model and set upper limits on anomalous production of such events.

  • 954. Abazov, V. M.
    et al.
    Åsman, Barbro
    Clément, Christophe
    Lager, Sara
    Strandberg, Jonas
    Zylberstejn, A.
    et al.,
    Search for first-generation scalar leptoquarks in p(p)over-bar collisions at root s=1.96 TeV2005In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 71, no 7, p. 071104-Article in journal (Refereed)
    Abstract [en]

    We report on a search for pair production of first-generation scalar leptoquarks (LQ) in p (p) over bar collisions at root s=1.96 TeV using an integrated luminosity of 252 pb(-1) collected at the Fermilab Tevatron collider by the D0 detector. We observe no evidence for LQ production in the topologies arising from LQ(LQ) over bar -> eqeq and LQ(LQ) over bar -> eq nu q, and derive 95% C.L. lower limits on the LQ mass as a function of beta, where beta is the branching fraction for LQ -> eq. The limits are 241 and 218 GeV/c(2) for beta=1 and 0.5, respectively. These results are combined with those obtained by D0 at root s=1.8 TeV, which increases these LQ mass limits to 256 and 234 GeV/c(2).

  • 955. Abazov, V. M.
    et al.
    Åsman, Barbro
    Clément, Christophe
    Lager, Sara
    Strandberg, Jonas
    Zylberstejn, A.
    et al.,
    Search for Wbb(-) and WH production in pp(-) collisions at root s=1.96 TeV2005In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 94, no 9, p. 091802-Article in journal (Refereed)
    Abstract [en]

    We present a search for Wb (b) over bar production in p (p) over bar collisions at root s=1.96 TeV in events containing one electron, an imbalance in transverse momentum, and two b-tagged jets. Using 174 pb(-1) of integrated luminosity accumulated by the D0 experiment at the Fermilab Tevatron collider, and the standard-model description of such events, we set a 95% C.L. upper limit on Wb (b) over bar production of 6.6 pb for b quarks with transverse momenta p(T)(b)> 20 GeV and b (b) over bar separation in pseudorapidity-azimuth space Delta R-bb> 0.75. Restricting the search to optimized b (b) over bar mass intervals provides upper limits on WH production of 9.0-12.2 pb for Higgs-boson masses of 105-135 GeV.

  • 956. Abazov, V. M.
    et al.
    Åsman, Barbro
    Clément, Christophe
    Strandberg, Jonas
    Zylberstejn, A.
    et al.,
    Measurement of the B-s(0) lifetime in the exclusive decay channel B-s(0)-> J/psi phi2005In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 94, no 4, p. 042001-Article in journal (Refereed)
    Abstract [en]

    Using the exclusive decay B-s(0)-->J/psi(mu(+)mu(-))phi(K+K-), we report the most precise single measurement of the B-s(0) lifetime. The data sample corresponds to an integrated luminosity of approximately 220 pb(-1) collected with the D0 detector at the Fermilab Tevatron Collider in 2002-2004. We reconstruct 337 signal candidates, from which we extract the B-s(0) lifetime, tau(B-s(0))=1.444(-0.090)(+0.098)(stat)+/-0.020(sys) ps. We also report a measurement for the lifetime of the B-0 meson using the exclusive decay B-0-->J/psi(mu(+)mu(-))K-*0(892)(K(+)pi(-)). We reconstruct 1370 signal candidates, obtaining tau(B-0)=1.473(-0.050)(+0.052)(stat)+/-0.023(sys) ps, and the ratio of lifetimes, tau(B-s(0))/tau(B-0)=0.980(-0.071)(+0.076)(stat)+/-0.003(sys).

  • 957. Abazov, V. M.
    et al.
    Åsman, Barbro
    Clément, Christophe
    Strandberg, Jonas
    Zylberstejn, A.
    et al.,
    Observation and properties of the X(3872) decaying to J/psi pi(+)pi(-) in p(p)over-bar collisions at root s=1.96 TeV2004In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 93, no 16, p. 162002-Article in journal (Refereed)
    Abstract [en]

    We report the observation of the X(3872) in the J/psipi(+)pi(-) channel, with J/psi decaying to mu(+)mu(-), in p (p) over bar collisions at roots=1.96 TeV. Using approximately 230 pb(-1) of data collected with the Run II D0 detector, we observe 522+/-100 X(3872) candidates. The mass difference between the X(3872) state and the J/psi is measured to be 774.9+/-3.1(stat)+/-3.0(syst) MeV/c(2). We have investigated the production and decay characteristics of the X(3872) and find them to be similar to those of the psi(2S) state.

  • 958.
    Abazov, V. M.
    et al.
    Joint Inst Nucl Res, Dubna, Russia..
    Åsman, Bengt
    KTH.
    Clement, Christophe
    KTH.
    Gollub, Nils
    KTH.
    Lager, S.
    Lund Univ, Lund, Sweden.;Royal Inst Technol, Stockholm, Sweden.;Stockholm Univ, S-10691 Stockholm, Sweden.;Uppsala Univ, Uppsala, Sweden..
    Soeldner-Rembold, S.
    Univ Manchester, Manchester, Lancs, England..
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Search for particles decaying into a Z boson and a photon in collisions p (p)over-bar at root s = 1.96 TeV (vol 641, pg 415, 2006)2009In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 670, no 4-5, p. 455-458Article in journal (Refereed)
  • 959. Abazov, V.M.
    et al.
    Gollub, Nils
    Strandberg, Jonas
    Zverev, E.G.
    Study of direct CP violation in B(+/-)-> J/psi K(+/-)(pi(+/-)) decays2008In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 100, no 21, p. 211802-Article in journal (Refereed)
    Abstract [en]

    We present a search for direct CP violation in B(+/-) -> J/psi K(+/-) (pi(+/-)) decays. The event sample is selected from 2: 8 fb(-1) of p (p) over bar collisions recorded by D0 experiment in run II of the Fermilab Tevatron Collider. The charge asymmetry A(CP)(B(+) -> J/psi K(+)) = +0: 0075 +/- 0: 0061(stat) +/- 0: 0030 (syst) is obtained using a sample of approximately 40 000 B(+/-) -> J/psi K(+/-) decays. The achieved precision is of the same level as the expected deviation predicted by some extensions of the standard model. We also measured the charge asymmetry A(CP) (B(+) -> J/psi pi(+)) = - 0: 09 +/- 0: 08(stat) +/- 0: 03(syst).

  • 960. Abazov, V.M.
    et al.
    Gollub, Nils
    Strandberg, Jonas
    University of Chicago.
    Zverev, E.G.
    et al.,
    First study of the radiation-amplitude zero in W gamma production and limits on anomalous WW gamma couplings at root s=1.96 TeV2008In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 100, no 24, p. 241805-Article in journal (Refereed)
    Abstract [en]

    We present results from a study of p (p) over bar -> W gamma+X events utilizing data corresponding to 0.7 fb(-1) of integrated luminosity at root s = 1.96 TeV collected by the D0 detector at the Fermilab Tevatron Collider. We set limits on anomalous WW gamma couplings at the 95% C.L. The one-dimensional 95% C.L. limits are 0.49 <kappa(gamma)< 1.51 and -0.12 <lambda(gamma)< 0.13. We make the first study of the charge-signed rapidity difference between the lepton and the photon and find it to be indicative of the standard model radiation-amplitude zero in the W gamma system.

  • 961. Abazov, V.M.
    et al.
    Gollub, Nils
    Strandberg, Jonas
    University of Chicago.
    Zverev, E.G.
    et al.,
    Measurement of sigma(p(p)over-bar -> Z plus X)Br(Z -> tau(+)tau(-)) at root s=1.96 TeV2009In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 670, no 4-5, p. 292-299Article in journal (Refereed)
    Abstract [en]

    We present a measurement of the cross section for Z boson production times the branching fraction to tau lepton pairs sigma(p (p) over bar -> Z + X)Br(Z -> tau(+)tau(-)) in p (p) over bar collisions at root s = 1.96 TeV. The measurement is performed in the channel in which one tau lepton decays into a muon and neutrinos. and the other tau lepton decays hadronically or into an electron and neutrinos. The data sample corresponds to an integrated luminosity of 1.0 fb(-1) collected with the DO detector at the Fermilab Tevatron Collider. The sample contains 1511 candidate events with an estimated 20% background from jets or muons misidentified as tau leptons. We obtain sigma . Br = 240 +/- 8 (star) +/- 12 (sys) +/- 15 (lum) pb, which is consistent with the standard model prediction.

  • 962. Abazov, V.M.
    et al.
    Gollub, Nils
    Strandberg, Jonas
    University of Chicago.
    Zverev, E.G.
    et al.,
    Measurement of the Lifetime of the B(c)(+/-) Meson in the Semileptonic Decay Channel2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 102, no 9, p. 092001-Article in journal (Refereed)
    Abstract [en]

    Using approximately 1.3 fb(-1) of data collected by the D0 detector between 2002 and 2006, we measure the lifetime of the B(c)(+/-) meson in the B(c)(+/-)-> J/psi mu(+/-)+X final state. A simultaneous unbinned likelihood fit to the J/psi+mu invariant mass and lifetime distributions yields a signal of 881 +/- 80(stat) candidates and a lifetime measurement of tau(B(c)(+/-))=0.448(-0.036)(+0.038)(stat)+/- 0.032(syst) ps.

  • 963. Abazov, V.M.
    et al.
    Gollub, Nils
    Strandberg, Jonas
    University of Chicago.
    Zverev, E.G.
    et al.,
    Search for a scalar or vector particle decaying into Z gamma in p(p)over-bar collisions at root s=1.96 TeV2009In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 671, no 3, p. 349-355Article in journal (Refereed)
    Abstract [en]

    We present a search for a narrow scalar or vector resonance decaying into Z gamma with a subsequent Z boson decay into a pair of electrons or moons. The data for this search were collected with the D circle divide detecror at the Fermilab Tevatron p (p) over bar collider at a center of mass energy root s = 1.96 TeV. Using 1.1 (1.0) fb(-1) of data, we observe 49 (50) candidate events in the electron (muon) channel, in good agreement with the standard model prediction. From the combination of both channels, we derive 95% C.L. upper limits on the cross section times branching fraction (sigma x B) into Z gamma. These limits range from 0.19 (0.20) pb for a scalar (vector) resonance mass of 600 GeV/c(2) to 2.5 (3.1) pb for a mass of 140 GeV/c(2).

  • 964. Abazov, V.M.
    et al.
    Gollub, Nils
    Strandberg, Jonas
    University of Chicago.
    Zverev, E.G.
    et al.,
    Search for Associated W and Higgs Boson Production in p(p)over-bar Collisions at root s=1.96 TeV2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 102, no 5, p. 051803-Article in journal (Refereed)
    Abstract [en]

    We present results of a search for WH -> l nu b (b) over bar production in p (p) over bar collisions based on the analysis of 1.05 fb(-1) of data collected by the D0 experiment at the Fermilab Tevatron, using a neural network for separating the signal from backgrounds. No signal-like excess is observed, and we set 95% C. L. upper limits on the WH production cross section multiplied by the branching ratio for H -> b (b) over bar for Higgs boson masses between 100 and 150 GeV. For a mass of 115 GeV, we obtain an observed (expected) limit of 1.5 (1.4) pb, a factor of 11.4 (10.7) times larger than the standard model prediction.

  • 965. Abazov, V.M.
    et al.
    Gollub, Nils
    Strandberg, Jonas
    University of Chicago.
    Zverev, E.G.
    et al.,
    Search for Neutral Higgs Bosons at High tan beta in the b(h/H/A) -> b tau(+)tau(-) Channel2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 102, no 5, p. 051804-Article in journal (Refereed)
    Abstract [en]

    The first search in p (p) over bar collisions at root s = 1.96 TeV for the production of neutral Higgs bosons in association with bottom quarks and decaying in two tau leptons is presented. The cross section for this process is enhanced in many extensions of the standard model, such as its minimal supersymmetric extension (MSSM) at large tan beta. The data, corresponding to an integrated luminosity of 328 pb(-1), were collected with the D0 detector at the Fermilab Tevatron Collider. An upper limit is set on the production cross section of neutral Higgs bosons in the mass range of 90 to 150 GeV, and this limit is used to exclude part of the MSSM parameter space.

  • 966. Abazov, V.M.
    et al.
    Gollub, Nils
    Strandberg, Jonas
    University of Michigan.
    Zverev, E.G.
    et al.,
    Search for W ' boson resonances decaying to a top quark and a bottom quark2008In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 100, no 21, p. 211803-Article in journal (Refereed)
    Abstract [en]

    We search for the production of a heavy W ' gauge boson that decays to third generation quarks in 0: 9 fb(-1) of p (p) over bar collisions at root s = 1: 96 TeV, collected with the D0 detector at the Fermilab Tevatron collider. We find no significant excess in the final-state invariant mass distribution and set upper limits on the production cross section times branching fraction. For a left-handed W ' boson with SM couplings, we set a lower mass limit of 731 GeV. For right-handed W ' bosons, we set lower mass limits of 739 GeV if the W ' boson decays to both leptons and quarks and 768 GeV if the W ' boson decays only to quarks. We also set limits on the coupling of the W ' boson to fermions as a function of its mass.

  • 967. Abazov, V.M.
    et al.
    Strandberg, Jonas
    University of Chicago.
    Zverev, E.G.
    Evidence for the Decay B(s)(0)-> D(s)((*))D(s)((*)) and a Measurement of Delta Gamma(CP)(s)/Gamma(s)2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 102, no 9, p. 091801-Article in journal (Refereed)
    Abstract [en]

    We search for the semi-inclusive process B(s)(0)-> D(s)((*))D(s)((*)) using 2.8 fb(-1) of pp collisions at s=1.96 TeV recorded by the D0 detector operating at the Fermilab Tevatron Collider. We observe 26.6 +/- 8.4 signal events with a significance above background of 3.2 standard deviations yielding a branching ratio of B(B(s)(0)-> D(s)((*))D(s)((*)))=0.035 +/- 0.010(stat.)+/- 0.011(syst.). Under certain theoretical assumptions, these double-charm final states saturate CP-even eigenstates in the B(s)(0) decays resulting in a width difference of Delta Gamma(CP)(s)/Gamma(s)=0.072 +/- 0.021(stat.)+/- 0.022(syst.).

  • 968. Abazov, V.M.
    et al.
    Strandberg, Jonas
    University of Chicago.
    Zverev, E.G.
    et al.,
    Measurement of the Angular and Lifetime Parameters of the Decays B(d)(0) -> J/psi K*(0) and B(s)(0) -> J/psi phi2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 102, no 3, p. 032001-Article in journal (Refereed)
    Abstract [en]

    We present measurements of the linear polarization amplitudes and the strong relative phases that describe the flavor-untagged decays B(d)(0) --> J/psi K*(0) and B(s)(0) --> J/psi phi in the transversity basis. We also measure the mean lifetime (tau) over bar (s) of the B(s)(0) mass eigenstates and the lifetime ratio (tau) over bar (s)/tau(d). The analyses are based on approximately 2.8 fb(-1) of data recorded with the D0 detector. From our measurements of the angular parameters we conclude that there is no evidence for a deviation from flavor SU( 3) symmetry for these decays and that the factorization assumption is not valid for the B(d)(0) --> J/psi K*(0) decay.

  • 969. Abazov, V.M.
    et al.
    Strandberg, Jonas
    University of Chicago.
    Zverev, E.G.
    et al.,
    Search for Large Extra Spatial Dimensions in the Dielectron and Diphoton Channels in p(p)over-bar Collisions at root s=1.96 TeV2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 102, no 5, p. 051601-Article in journal (Refereed)
    Abstract [en]

    We report on a search for large extra spatial dimensions in the dielectron and diphoton channels using a data sample of 1: 05 fb(-1) of p (p) over bar collisions at a center-of-mass energy of 1.96 TeV collected by the D0 detector at the Fermilab Tevatron Collider. The invariant mass spectrum of the data agrees well with the prediction of the standard model. We find the most restrictive 95% C. L. lower limits on the effective Planck scale between 2.1 and 1.3 TeV for 2 to 7 extra dimensions.

  • 970. Abazov, V.M.
    et al.
    Åsman, Björn
    Clément, Christophe
    Lager, Sara
    Strandberg, Jonas
    Stockholms universitet.
    Zylberstejn, A.
    et al.,
    Search for doubly charged Higgs boson pair production in the decay to mu(+)mu(+)mu(-)mu(-) in p(p)over-bar collisions at root s=1.96 TeV2004In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 93, no 14, p. 141801-Article in journal (Refereed)
    Abstract [en]

    A search for pair production of doubly charged Higgs bosons in the process p (p) over bar -->H++H---->mu(+)mu(+)mu(-)mu(-) is performed with the D0 run II detector at the Fermilab Tevatron. The analysis is based on a sample of inclusive dimuon data collected at an energy of roots=1.96 TeV, corresponding to an integrated luminosity of 113 pb(-1). In the absence of a signal, 95% confidence level mass limits of M(H-L(+/-+/-))>118.4 GeV/c(2) and M(H-R(+/-+/-))>98.2 GeV/c(2) are set for left-handed and right-handed doubly charged Higgs bosons, respectively, assuming 100% branching into muon pairs.

  • 971. Adam Bourdarios, C.
    et al.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    et, al.
    Statistical combination of several important standard model Higgs boson search channels2009Report (Refereed)
    Abstract [en]

        In this note we describe statistical procedures for combination of results from independent searches for the Higgs boson. Here only the Standard Model Higgs is considered, although the methods can easily be extended to non-standard Higgs models as well as to other searches. The methods are applied to Monte Carlo studies of four important search channels: H to tau+ tau-, H to W+ W- to e-nu mu-nu, H to gamma gamma, and H to ZZ)(*) to 4 leptons. The statistical treatment relies on a large sample approximation that is expected to be valid for an integrated luminosity of at least 2 fb-1 . Results are presented for the expected statistical significance of discovery and expected exclusion limits.

  • 972. Ahmed, S.N
    et al.
    Strandberg, Jonas
    Stockholms universitet.
    Zverev, E.G.
    et al.,
    The D0 Silicon Microstrip Tracker2011In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 634, no 1, p. 8-46Article in journal (Refereed)
    Abstract [en]

    This paper describes the mechanical design, the readout chain, the production, testing and the installation of the Silicon Microstrip Tracker of the D0 experiment at the Fermilab Tevatron collider. In addition, we describe the performance and operational experience of the detector during the experiment data collection between 2001 and 2010.

  • 973. Angerami, A
    et al.
    Kastanas, Konstatinos A.
    KTH, School of Engineering Sciences (SCI), Physics.
    Lund-Jensen, Bengt
    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.
    et al.,
    Measurements of photo-nuclear jet production in Pb plus Pb collisions with ATLAS2017In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 967, p. 277-280Article in journal (Refereed)
    Abstract [en]

    Ultra-peripheral heavy ion collisions provide a unique opportunity to study the parton distributions in the colliding nuclei via the measurement of photo-nuclear jet production. An analysis of jet production in ultra-peripheral Pb+Pb collisions at root S-NN = 5.02 TeV performed using data collected with the ATLAS detector in 2015 is described. The data set corresponds to a total Pb+Pb integrated luminosity of 0.38 nb(-1). The ultra-peripheral collisions are selected using a combination of forward neutron and rapidity gap requirements. The cross-sections, not unfolded for detector response, are compared to results from PYTHIA Monte Carlo simulations re-weighted to match a photon spectrum obtained from the STARLIGHT model. Qualitative agreement between data and these simulations is observed over a broad kinematic range suggesting that using these collisions to measure nuclear parton distributions is experimentally realisable.

  • 974. Armbruster, A.
    et al.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    et, al.
    Higgs boson searches in gluon fusion and vector boson fusion using the H $\to$ WW decay mode2009Report (Refereed)
    Abstract [en]

    The prospects for Higgs searches in the H + 0j (H to WW to e-nu mu-nu ), H + 2j (H to WW to e-nu mu-nu ), and H + 2 j (H to WW to l-nu qq) channels at ATLAS are presented, including realistic effects such as trigger efficiencies and detector misalignment, with an emphasis on practical methods to estimate the backgrounds using control samples in data. With 10 fb−1 of integrated luminosity, one would expect to be able to discover a Standard Model Higgs boson in the mass range 135 < mH < 190 GeV and to be able to measure its mass with a precision of about 7 GeV if its true mass is 130 GeV or about 2 GeV if its true mass is 160 GeV.

  • 975. ATLAS Collaboration,
    et al.
    Lund-Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Sidebo, 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.
    et al.,
    Measurement of exclusive γγ→ℓ+ℓ- production in proton-proton collisions at √s=7 TeV with the ATLAS detector2015In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 749, p. 242-261Article in journal (Refereed)
    Abstract [en]

    This Letter reports a measurement of the exclusive γγ→ℓ+ℓ- (ℓ=e, μ) cross-section in proton-proton collisions at a centre-of-mass energy of 7 TeV by the ATLAS experiment at the LHC, based on an integrated luminosity of 4.6 fb-1. For the electron or muon pairs satisfying exclusive selection criteria, a fit to the dilepton acoplanarity distribution is used to extract the fiducial cross-sections. The cross-section in the electron channel is determined to be σγγ→e+e-excl.=0.428 ± 0.035 (stat.) ± 0.018 (syst.) pb for a phase-space region with invariant mass of the electron pairs greater than 24 GeV, in which both electrons have transverse momentum pT>12 GeV and pseudorapidity |η|<2.4. For muon pairs with invariant mass greater than 20 GeV, muon transverse momentum pT>10 GeV and pseudorapidity |η|<2.4, the cross-section is determined to be σγγ→μ+μ-excl.=0.628 ± 0.032 (stat.) ± 0.021 (syst.) pb. When proton absorptive effects due to the finite size of the proton are taken into account in the theory calculation, the measured cross-sections are found to be consistent with the theory prediction.

  • 976.
    Balek, Petr
    et al.
    Weizmann Inst Sci, Fac Phys, Dept Particle Phys & Astrophys, 234 Herzl St, IL-76100 Rehovot, Israel..
    Balek, P.
    Weizmann Inst Sci, Dept Particle Phys, Rehovot, Israel..
    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. 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..
    Charged-hadron suppression in Pb plus Pb and Xe plus Xe collisions measured with the ATLAS detector2019In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 982, p. 571-574Article in journal (Refereed)
    Abstract [en]

    The ATLAS detector at the LHC recorded 0.49 nb(-1) of Pb+Pb collisions and 25 of pp(-1) collisions, both at the center-of-mass energy 5.02 TeV per nucleon pair. Recently, ATLAS also recorded 30 mu b(-1) of Xe+Xe collisions at the center-of-mass energy 5.44 TeV, which provides a new opportunity to study the system-size dependence of the charged-hadron production in heavy-ion collisions. The large acceptance of the ATLAS detector allows to measure the spectra of charged hadrons in a wide range of pseudorapidity and transverse momentum. The nuclear modification factors R-AA are constructed as a ratio of the spectra measured in Pb+Pb or Xe+Xe collisions to that measured in pp collisions. The R-AA obtained in the two systems are presented for different centrality intervals and the results are discussed.

  • 977.
    Bold, Tomasz
    et al.
    AGH Univ Sci & Technol, Krakow, Poland..
    Bold, T.
    AGH Univ Sci & Technol, Fac Phys & Appl Comp Sci, Krakow, Poland..
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Phys Dept, Stockholm, Sweden..
    Ohm, Christian
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Phys Dept, Stockholm, Sweden..
    Ripellino, Giulia
    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..
    Measurement of the azimuthal anisotropy of charged particles in 5.02 TeV Pb+Pb and 5.44 TeV Xe+Xe collisions with ATLAS2019In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 982, p. 391-394Article in journal (Refereed)
    Abstract [en]

    The data collected by the ATLAS experiment during the 2015 Pb+Pb and 2017 Xe+Xe LHC runs offer new opportunities to study charged particle azimuthal anisotropy. The high-statistics Pb+Pb sample allows for a detailed study of the azimuthal anisotropy of produced particles. This should improve the understanding of initial conditions of nuclear collisions, hydrodynamical behavior of quark-gluon plasma and parton energy loss. New ATLAS measurements of differential and global Fourier harmonics of charged particles (v(n)) in 5.02 TeV Pb+Pb and 5.44 TeV Xe+Xe collisions in a wide range of transverse momenta, pseudorapidity (vertical bar eta vertical bar < 2.5) and collision centrality are presented. The higher order harmonics, sensitive to fluctuations in the initial state, are measured up to n = 7 using the two-particle correlation, cumulant and scalar product methods. The dynamic properties of QGP are studied using a recently-proposed modified Pearson's correlation coefficient, rho(v(n)(2), p(T)), between the event-wise mean transverse momentum and the magnitude of the flow vector in 5.02 TeV Pb+Pb and p+Pb collisions. Several important observations are made. The elliptic and triangular flow harmonics show an interesting universal p(T)-scaling. A linear correlation between the v(2) and v(3) coefficients at low and high p(T) ranges is observed and quantified. The correlation coefficient for v(2) is found to be negative in peripheral and positive in central Pb+Pb collisions. The value for v(3) is found to be much smaller than for v(2) and have similar centrality behavior as the v(2).

  • 978.
    Citron, Zvi
    et al.
    Ben Gurion Univ Negev, Beer Sheva, Israel..
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Phys Dept, Stockholm, Sweden..
    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..
    Electroweak probes of small and large systems with the ATLAS detector2019In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 982, p. 603-606Article in journal (Refereed)
    Abstract [en]

    Measurements of isolated prompt photon and massive electroweak (W and Z) boson production in different collision systems are of great interest to understand the partonic structure of heavy nuclei, and serve as a constraint on the initial state in larger collision systems. These channels are sensitive to a variety of effects such as the modification of the parton densities in nuclei in certain kinematic regions, and the energy loss of partons as they undergo multiple interactions in the nucleus before the hard parton-parton scattering. High-statistics samples of lead-lead and proton-lead collision data at root s(NN)=5.02 TeV and 8.16 TeV, respectively, taken by the ATLAS experiment at the LHC, as well as proton-proton comparison data at analogous collision energies, allow for a detailed study of these phenomena in data and comprehensive comparisons to the predictions of a variety of theoretical approaches. This paper presents the latest ATLAS results in these topics, including updated results on inclusive prompt photon production in proton-lead collisions over a broad kinematic range and high-precision W boson results in lead lead collisions.

  • 979.
    Derendarz, Dominik
    et al.
    PAS, Inst Nucl Phys, Ul Radzikowskiego 152, PL-31342 Krakow, Poland..
    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. 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..
    Measurement of the flow harmonic correlations in pp, p plus Pb and low multiplicity Pb plus Pb collisions with the ATLAS detector at the LHC2019In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 982, p. 479-482Article in journal (Refereed)
    Abstract [en]

    Recent measurements of the correlations between flow harmonics obtained using four-particle symmetric cumulants and three-particle asymmetric cumulants with the ATLAS detector at the LHC are described. The data sets of pp, p+Pb and peripheral Pb+Pb collisions at various energies are analyzed, aiming to probe the long-range collective nature of multi-particle production in small systems. The sensitivity of the standard cumulant method to non-flow correlations is investigated by introducing the subevents method. A systematic reduction of non-flow effects is observed when using the two-subevent method. Further reduction is observed with the three-subevent method that is consistent with the results obtained with the four-subevent one. A negative correlation between v(2) and v(3) and a positive correlation between v(2) and v(4), for all studied collision systems and over full multiplicity range, is observed. The correlation strength computed as symmetric cumulants normalized by the < v(n)(2)> is similar for all collision systems and weakly depends on multiplicity. These measurements provide new evidence for long-range multi-particle collectivity in small collision systems and quantify the nature of its event-by-event fluctuations.

  • 980. Di Marco, E.
    et al.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics.
    Observation of the Higgs boson in the H → W+W-(*) → ℓ+νℓ-ν final state2016In: Discovery of the Higgs Boson, World Scientific Publishing Co. Pte. Ltd. , 2016, p. 211-244Chapter in book (Other academic)
    Abstract [en]

    After analysing the full LHC Run 1 data set, the ATLAS and CMS experiments both observed an excess of events above the expected background in the H → W+W-(*) → ℓ+νℓ-ν channel (ℓ = e, μ) consistent with the expectations from the SM Higgs boson with a mass of 125 GeV. The probability to observe an excess equal to or larger than the one seen, under the background-only hypothesis, corresponded to a significance of 6.1 standard deviations for ATLAS (5.8 standard deviations expected) and 4.3 standard deviations for CMS (5.8 standard deviations expected). The observed σ/σSM value for mH = 125 GeV was 1.09+0.23 -0.21 for ATLAS and 0.72 ± 0.20 for CMS. The 0+ spin-parity hypothesis of the SM was favoured by the data over a narrow resonance with JP = 2+ or JP = 0- decaying into W+W-. The results were consistent between the two experiments and provided strong evidence for a SM-like Higgs boson decaying into a W boson pair. 

  • 981. G., Aad
    et al.
    Jovicevic, J.
    KTH, School of Engineering Sciences (SCI), Physics.
    Kuwertz, E. S.
    KTH, School of Engineering Sciences (SCI), Physics.
    Lund-Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Morley, A. K.
    KTH, School of Engineering Sciences (SCI), Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    et.al, .
    Search for new phenomena in events with three or more charged leptons in pp collisions at √s=8 TeV with the ATLASdetector2015In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2015, no 8Article in journal (Refereed)
    Abstract [en]

    A generic search for anomalous production of events with at least three charged leptons is presented. The data sample consists of pp collisions at s=8" role="presentation" style="box-sizing: border-box; display: inline-table; line-height: normal; letter-spacing: normal; word-spacing: normal; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; position: relative;">s√=8s=8 TeV collected in 2012 by the ATLAS experiment at the CERN Large Hadron Collider, and corresponds to an integrated luminosity of 20.3 fb−1. Events are required to have at least three selected lepton candidates, at least two of which must be electrons or muons, while the third may be a hadronically decaying tau. Selected events are categorized based on their lepton flavour content and signal regions are constructed using several kinematic variables of interest. No significant deviations from Standard Model predictions are observed. Model-independent upper limits on contributions from beyond the Standard Model phenomena are provided for each signal region, along with prescription to re-interpret the limits for any model. Constraints are also placed on models predicting doubly charged Higgs bosons and excited leptons. For doubly charged Higgs bosons decaying to  or μτ, lower limits on the mass are set at 400 GeV at 95% confidence level. For excited leptons, constraints are provided as functions of both the mass of the excited state and the compositeness scale Λ, with the strongest mass constraints arising in regions where the mass equals Λ. In such scenarios, lower mass limits are set at 3.0 TeV for excited electrons and muons, 2.5 TeV for excited taus, and 1.6 TeV for every excited-neutrino flavour.

  • 982.
    Grabowska-Bold, Iwona
    et al.
    AGH Univ Sci & Technol, Krakow, Poland..
    Grabowska-Bold, I
    AGH Univ Sci & Technol, Fac Phys & Appl Comp Sci, Krakow, Poland..
    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..
    Highlights from the ATLAS experiment2019In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 982, p. 8-14Article in journal (Refereed)
    Abstract [en]

    This report provides an overview of the new results obtained by the ATLAS Collaboration at the LHC, which were presented at the Quark Matter 2018 conference. These measurements were covered in 12 parallel talks, one flash talk and 11 posters. In this document, a discussion of results is grouped into four areas: electromagnetic interactions, jet quenching, quarkonia and heavy-flavour production, and collectivity in small and larger systems. Measurements from the xenon-xenon collisions based on a short run collected in October 2017 are reported for the first time.

  • 983. Jia, J Y
    et al.
    Kastanas, Konstatinos A.
    KTH, School of Engineering Sciences (SCI), Physics.
    Lund-Jensen, Bengt
    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.
    et al.,
    Heavy Ion Results from ATLAS2017In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 967, p. 51-58Article in journal (Refereed)
    Abstract [en]

    These proceedings provide an overview of the new results obtained with the ATLAS detector at the LHC, which were presented in the Quark Matter 2017 conference. These results were covered by twelve parallel talks, one flash talk and eleven posters. These proceedings group these results into five areas: initial state, jet quenching, quarkonium production, longitudinal flow dynamics, and collectivity in small systems.

  • 984. Laycock, P. J.
    et al.
    Chelstowska, M. A.
    Donszelmann, T. C.
    Guenther, J.
    Nairz, A.
    Nikolaidou, R.
    Shabalina, E.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Taffard, A.
    Wang, S.
    ATLAS data preparation in run 22017In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 898, no 4, article id 042050Article in journal (Refereed)
    Abstract [en]

    In this contribution, the data preparation workflows for Run 2 are presented. The challenges posed by the excellent performance and high live time fraction of the LHC are discussed, and the solutions implemented by ATLAS are described. The prompt calibration loop procedures are described and examples are given. Several levels of data quality assessment are used to quickly spot problems in the control room and prevent data loss, and to provide the final selection used for physics analysis. Finally the data quality efficiency for physics analysis is shown.

  • 985.
    Perepelitsa, Dennis, V
    et al.
    Univ Colorado, Boulder, CO 80309 USA..
    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. Royal Inst Technol, Phys Dept, Stockholm, Sweden..
    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..
    Photon-tagged measurements of jet quenching with ATLAS2019In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 982, p. 595-598Article in journal (Refereed)
    Abstract [en]

    Events containing a high transverse momentum (p(T)) prompt photon offer a useful way to study the dynamics of the hot, dense medium produced in heavy ion collisions. Because photons do not carry color charge, they are unaffected by the medium, and thus provide information about the momentum, direction, and flavor (quark or gluon) of the associated hard-scattered parton before it begins to shower and become quenched. In particular, the presence of a high-p(T) photon can be used to select pp and Pb+Pb events with the same configuration before quenching, limiting the effects of quenching-induced selection biases present in other jet measurements. The large statistics pp and Pb+Pb data delivered by the LHC in 2015 allow for a detailed study of photon-tagged jet quenching effects, such as the overall parton energy loss and modified structure of the component of the shower which remains correlated with the initial parton direction (e.g. in cone). In this proceeding, photon-tagged measurements of jet quenching by ATLAS are reported.

  • 986.
    Puri, Akshat
    et al.
    Univ Illinois, Champaign, IL 61820 USA..
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Phys Dept, Stockholm, Sweden..
    Ohm, Christian
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Phys Dept, Stockholm, Sweden..
    Ripellino, Giulia
    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.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    CERN, Geneva, Switzerland..
    Measurement of angular and momentum distributions of charged particles within and around jets in Pb plus Pb and pp collisions at root s(NN)=5.02 TeV with ATLAS at the LHC2019In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 982, p. 177-179Article in journal (Refereed)
    Abstract [en]

    Studies of the fragmentation of jets into charged particles in heavy-ion collisions can help in understanding the mechanism of jet quenching by the hot and dense QCD matter created in such collisions, the quark-gluon plasma. These proceedings present a measurement of the angular distribution of charged particles around the jet axis in root s(NN) = 5.02 TeV Pb+Pb and pp collisions, done using the ATLAS detector at the LHC. The measurement is performed inside jets reconstructed with the anti-k(t) algorithm with radius parameter R = 0.4, and is extended to regions outside the jet cone. Results are presented as a function of Pb+Pb collision centrality, and both jet and charged-particle transverse momenta.

  • 987.
    Spousta, Martin
    et al.
    Charles Univ Prague, Fac Math & Phys, V Holesovickach 2, Prague 18000, Czech Republic..
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Phys Dept, Stockholm, Sweden..
    Ohm, Christian
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Phys Dept, Stockholm, Sweden..
    Ripellino, Giulia
    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..
    Jet suppression and jet substructure in Pb plus Pb and Xe plus Xe collisions with the ATLAS detector2019In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 982, p. 611-614Article in journal (Refereed)
    Abstract [en]

    This short summary presents latest measurements of the nuclear modification factor, R-AA, for R = 0.4 jets in Pb+Pb collisions at root s(NN) = 5.02 TeV with the ATLAS detector at the LHC. The analysis is performed over a large range of transverse momentum, up to p(T) = 1 TeV, and differentially in jet p(T), rapidity, and collision centrality. The jet R-AA is measured also differentially in the jet mass, m, which provides new information on the dependence of the energy loss on the substructure of jets. Latest results by ATLAS on the dijet momentum balance in Xe+Xe collisions at root s(NN) = 5.44 TeV are presented and compared to the same quantity measured in Pb+Pb collisions at root s(NN) = 5.02 TeV. These recent measurements should help us understand mechanisms of parton energy loss and properties of hot and dense matter created in heavy-ion collisions.

  • 988.
    Steinberg, Peter
    et al.
    Brookhaven Natl Lab, Upton, NY 11973 USA.;Brookhaven Natl Lab, Phys Dept, Upton, NY USA..
    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. Royal Inst Technol, Phys Dept, Stockholm, Sweden..
    Zwalinski, L.
    CERN, Geneva, Switzerland..
    et al.,
    Electromagnetic processes with quasireal photons in Pb plus Pb collisions: QED, QCD, and the QGP2019In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 982, p. 259-262Article in journal (Refereed)
    Abstract [en]

    Electromagnetic processes, both photon-photon and photon-nucleus, are shown to be useful in studying aspects of QED, QCD, and potentially the QGP. Using lead-lead collisions at root s(NN) = 5.02 TeV, the ATLAS detector has performed measurements of exclusive dimuon production, light-by-light scattering (via exclusive diphoton production), and photo-nuclear dijet production. These are all important examples of ultraperipheral collisions, where the nuclei do not interact hadronically. A recent study of the opening angles of dimuons produced in hadronic heavy-ion collisions, after subtracting heavy-flavor backgrounds, demonstrates that the dimuons carry information correlated with the overlap geometry, potentially about the density of charges in the QGP itself.

  • 989.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Measurement of R = B(t $\to$ Wb)/B(t $\to$ Wq) at D02005In: Int. J. Mod. Phys., Vol. A20, p. 3200-3202Article in journal (Refereed)
  • 990.
    Strandberg, Jonas
    University of Michigan, USA.
    Search for associated Higgs boson production at D02008In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 110, no 4Article in journal (Refereed)
    Abstract [en]

    Using 1 fb-1 of data the DØ collaboration has searched for the production of a Higgs boson in association with a W or a Z boson. The W or Z boson is required to decay leptonically and whereas the Higgs boson decays into a bbar b pair. Searches in these final states are the most sensitive for a Higgs boson with a mass less than about 130 GeV/c2. No evidence for Higgs boson production has been observed and 95% C.L. upper limits on the Higgs boson production cross section are derived.

  • 991.
    Strandberg, Jonas
    Stockholms universitet.
    Top quarks at the Tevatron: Measurements of the top quark production and decay with the D0 experiment2006Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis presents two measurements of the top quark using 230 pb-1 of data taken with the D0 detector at the Tevatron accelerator. The first measurement determines the top pair production cross section at sqrt(s)=1.96 TeV in proton-antiproton collisions. In the standard model of particle physics the top quark decays almost exclusively into a W boson and a b quark. Candidate events are selected by requiring that at least one jet in the event is tagged with the secondary vertex algorithm. The measured top pair production cross section is:

    8.6 +1.6-1.5 (stat. + syst.) +- 0.6 (lumi.) pb.

    The second measurement uses the observed and predicted number of events with 0, 1 and 2 b-tagged jets to estimate the ratio R:

    R = B(t->Wb) / B(t->Wq)

    where q stands for any down-type quark. The measured value is

    R = 1.03 +0.19-0.17 (stat. + syst.)

    in good agreement with the standard model prediction of R=1. The result can be used to obtain a lower limit for R:

    R > 0.61 (95% C.L.).

  • 992.
    Strandberg, Jonas
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Collaboration, A T L A S
    Search for Higgs to WW (ℓνℓν, ℓνqq) with the ATLAS detector2011In: Proceedings of Science, Sissa Medialab Srl , 2011Conference paper (Refereed)
    Abstract [en]

    Higgs boson searches in the H&gt;WW(∗)→ℓνℓν (ℓ = e,μ) and the H→WW(∗)→ℓvqq decay modes, using 1.04 fb-1 of proton-proton collision data delivered by the large hadron collider (LHC) at a centre-of-mass energy of 7 TeV collected with the ATLAS detector, are presented. An upper bound is placed on the Higgs boson production cross-section as a function of mH. The H→WW(∗)→ℓνℓν analysis excludes a Higgs boson with a mass in the range from 158 GeV to 186 GeV at 95% confidence level, while the expected Higgs boson mass exclusion range is 142 ≤ mH ≤ 186 GeV. An excess of events in data corresponding to more than 2σ significance is observed for the Higgs boson mass range from 126 GeV to 158 GeV The H→WW(∗)→ℓνqq analysis place limits on the Higgs boson cross section that are between 1.4 to 20 times the expected standard model cross section in the mass range from 240 GeV to 600 GeV.

  • 993.
    Zhou, Mingliang
    et al.
    SUNY Stony Brook, Dept Chem, Stony Brook, NY 11794 USA..
    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..
    Flow fluctuations in Pb plus Pb collisions at root s(NN)=5.02 TeV with the ATLAS detector2019In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 982, p. 323-326Article in journal (Refereed)
    Abstract [en]

    Measurements of four-particle cumulants c(n){4} for n = 1, 2, 3, 4 are presented using 470 mu b(-1) of Pb+Pb collisions at root s(NN) = 5.02 TeV with the ATLAS detector at the LHC. These cumulants provide information on the event-by-event fluctuations of single harmonics p(v(n)). For the first time, a negative c(1){4} is observed. The c(4){4} is found to be negative in central collisions but changes sign around 20-25% centrality. This behavior is consistent with a nonlinear contribution to v(4) that is proportional to v(2)(2). c(2){4} and c(3){4} are calculated using two reference event classes in order to investigate the influence of volume fluctuations. Over most of the centrality range, c(2){4} and c(3){4} are found to be negative, while in the ultra-central collisions, c(2){4} changes sign and becomes positive, suggesting a deviation from Gaussian behavior in the event-by-event fluctuation of v(2). The magnitudes of the sign change are also found to be dependent of the event class definition .

17181920 951 - 993 of 993
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