Measurement of the cross-section for b-jets produced in association with a Z boson at root s=7 TeV with the ATLAS detector ATLAS Collaboration

A measurement is presented of the inclusive cross-section for b-jet production in association with a Z boson in pp collisions at a centre-of-mass energy of root s = 7 TeV. The analysis uses the data sample collected by the ATLAS experiment in 2010, corresponding to an integrated luminosity of approximately 36 pb(-1). The event selection requires a Z boson decaying into high P-T electrons or muons, and at least one b-jet, identified by its displaced vertex, with transverse momentum p(T) > 25 GeV and rapidity vertical bar y vertical bar < 2.1. After subtraction of background processes, the yield is extracted from the vertex mass distribution of the candidate b-jets. The ratio of this cross-section to the inclusive Z cross-section (the average number of b-jets per Z event) is also measured. Both results are found to be in good agreement with perturbative QCD predictions at next-to-leading order

DoI position resolution in a continuous LaBr3(Ce) scintillation crystal for gamma-ray imaging

A Monte Carlo simulation of a 50mm 750mm 74mm continuous crystal has been developed to investigate the correlation between the scintillation light width (\u3c3) and the Depth of Interaction (DoI) within the crystal. Our studies are based on a LaBr3(Ce) crystal, in order to take advantage of its high light yield to reduce the statistic uncertainties on the estimators of the \u3c3. The first one, the standard deviation of the light distribution, has demonstrated a poor, though linear, correlation to DoI, that is not experimentally detectable. Otherwise, the second estimator,N/I, is the ratio of the total number of photoelectrons to the maximum number of photoelectrons collected from a single anode, in a scintillation event. N/I has been found to have the best correlation to DoI, that provides 2 mm resolution

Observation of a peaking structure in the J/psi phi mass spectrum from B-+/- -&gt; J/psi phi K-+/- decays

A peaking structure in the J/ψφ mass spectrum near threshold is observed in B ±→J/ψφK± decays, produced in pp collisions at √s=7 TeV collected with the CMS detector at the LHC. The data sample, selected on the basis of the dimuon decay mode of the J/ψ, corresponds to an integrated luminosity of 5.2 fb-1. Fitting the structure to an S-wave relativistic Breit-Wigner lineshape above a three-body phase-space nonresonant component gives a signal statistical significance exceeding five standard deviations. The fitted mass and width values are m = 4148.0 ± 2.4 (stat.) ± 6.3 (syst.)MeV and Γ=28-11 +15(stat.)±19(syst.)MeV, respectively. Evidence for an additional peaking structure at higher J/ψφ mass is also reported. © 2014 The Authors