Abstract: The ATLAS experiment at the LHC has measured the centrality dependence of charged particle pseudorapidity distributions over vertical bar eta vertical bar < 2 in lead-lead collisions at a nucleon-nucleon centre-of-mass energy of root s(NN) = 2.76 TeV. In order to include particles with transverse momentum as low as 30 MeV, the data were recorded with the central solenoid magnet off. Charged particles were reconstructed with two algorithms (2-point “tracklets” and full tracks) using information from the pixel detector only. The lead-lead collision centrality was characterized by the total transverse energy in the forward calorimeter in the range 3.2 < vertical bar eta vertical bar< 4.9. Measurements are presented of the per-event charged particle pseudorapidity distribution, dN(ch)/d eta, and the average charged particle multiplicity in the pseudorapidity interval vertical bar eta vertical bar < 0.5 in several intervals of collision centrality. The results are compared to previous mid-rapidity measurements at the LHC and RHIC. The variation of the mid-rapidity charged particle yield per colliding nucleon pair with the number of participants is consistent with lower root s(NN) results. The shape of the dN(ch)/d eta distribution is found to be independent of centrality within the systematic uncertainties of the measurement.

Abstract: A combined search for the Standard Model Higgs boson with the ATLAS experiment at the LHC using datasets corresponding to integrated luminosities from 1.04 fb(-1) to 4.9 fb(-1) of pp collisions collected at root s = 7 TeV is presented. The Higgs boson mass ranges 112.9-115.5 GeV, 131-238 GeV and 251-466 GeV are excluded at the 95% confidence level (CL), while the range 124-519 GeV is expected to be excluded in the absence of a signal. An excess of events is observed around m(H) similar to 126 GeV with a local significance of 3.5 standard deviations (sigma). The local significances of H -> gamma, H -> ZZ(()*()) -> l(+)l(-)l'(+)l'(-) and H -> WW(*()) l(+)nu l'(-)(nu) over bar, the three most sensitive channels in this mass range, are 2.8 sigma, 2.1 sigma and 1.4 sigma. respectively. The global probability for the background to produce such a fluctuation anywhere in the explored Higgs boson mass range 110-600 GeV is estimated to be similar to 1.4% or, equivalently, 2.2 sigma.

Abstract: The C-13(O-18,O-16)C-15 reaction has been studied at 84 MeV incident energy. The ejectiles have been detected at forward angles and C-15 excitation energy spectra have been obtained up to about 20 MeV. Several known bound and resonant states of C-15 have been identified together with two unknown structures at 10.5 MeV (FWHM = 2.5 MeV) and 13.6 MeV (FWHM = 2.5 MeV). Calculations based Oil the removal of two uncorrelated neutrons from the projectile describe a significant part of the continuum observed in the energy spectra. In particular the structure at 10.5 MeV is dominated by a resonance of C-15 near the C-13 + n + n threshold. Similar structures are found in nearby nuclei such as C-14 and Be-11.

Abstract: This Letter presents a search for singly produced vector-like quarks, Q, coupling to light quarks, q. The search is sensitive to both charged current (CC) and neutral current (NC) processes, pp -> Qq -> Wqq' and pp -> Qq -> Zqq' with a leptonic decay of the vector gauge boson. In 1.04 fb(-1) of data taken in 2011 by the ATLAS experiment at a center-of-mass energy root s = 7 TeV, no evidence of such heavy vector-like quarks is observed above the expected Standard Model background. Limits on the heavy vector-like quark production cross section times branching ratio as a function of mass m(Q) are obtained. For a coupling K-qQ = v/m(Q), where v is the Higgs vacuum expectation value, 95% C.L. lower limits on the mass of a vector-like quark are set at 900 GeV and 760 GeV from CC and NC processes, respectively.

Abstract: This Letter reports a measurement of the W W production cross section in root s = 7 TeV pp collisions using data corresponding to an integrated luminosity of 1.02 fb(-1) collected with the ATLAS detector. Using leptonic decays of oppositely charged W bosons, the total measured cross section is sigma (pp -> W W) = 54.4 +/- 4.0 (stat.) +/- 3.9 (syst.) +/- 2.0 (lumi.) pb, consistent with the Standard Model prediction of sigma (pp -> W W)= 44.4 +/- 2.8 pb. Limits on anomalous electroweak triple-gauge couplings are extracted from a fit to the transverse-momentum distribution of the leading charged lepton in the event.