Backgrounds for rare muonic B-meson decays in ATLAS

The work gives an overview of expected exclusive backgrounds for rare muonic B-meson decays in ATLAS. Based on theoretical calculations and a modelling in Generators, followed by phase space cuts according to fiducial detector volume and trigger acceptance, the authors classify all possible backgrounds according to their importance and select those requiring full detector simulation. The most importat background comes from $B_d^0 \to \pi^- \mu^+ \nu_{\mu}$, when a charged pion decays in a detector volume producing a secondary muon. Similar mechanism would lead to a background comming from B-mesons decaying to two charged hadrons. Another important background is from $B^+ \to \mu^+\mu^-l^+ \nu$.This note gives an overview of expected exclusive backgrounds for rare muonic B–meson decays at ATLAS from the theoretical point of view. The goal of this work is to show which of backgrounds are most important for further full detector simulation. It is shown that the most important noncombinatorial background comes from $B_d^0 \to \pi^- \mu^+ \nu_{\mu}$ fake rate. Another important BG sources are $B^+ \to \mu^+\mu^-\ell^+ \nu_{\ell}, B_c^+ \to J/\psi (\mu^+ \mu^-) \ell \nu_{\ell}$ and two-body hadronic B–meson decays

Feasibility of Beauty Baryon Polarization Measurement in Lambda0 J/psi Decay Channel by Atlas-LHC

The possibility of beauty baryon polarization measurement by cascade decay angular distribution analysis in the channel Lambda0 J/psi --> p pi- l+ l- is demonstrated. The error analysis shows that in the proposed LHC experiment ATLAS at the luminosity $10^{4} pb^{-1}$ the polarization can be measured with the statistical precision better than $\delta=0.010$ for Lambda_b0 and $\delta=0.17$ for Xi_b0.Comment: 12 pages (LaTeX + AMS-LaTeX) and 3 figures in postscript (uuencoded, compressed tar file included at the end of the paper), PRA-HEP-94/

Bottom Production

We review the prospects for bottom production physics at the LHC.Comment: 74 pages, Latex, 71 figures, to appear in the Report of the ``1999 CERN Workshop on SM physics (and more) at the LHC'', P. Nason, G. Ridolfi, O. Schneider G.F. Tartarelli, P. Vikas (conveners

Hunt for new phenomena using large jet multiplicities and missing transverse momentum with ATLAS in 4.7 fb−1 of s√=7TeV proton-proton collisions

Results are presented of a search for new particles decaying to large numbers of jets in association with missing transverse momentum, using 4.7 fb−1 of pp collision data at s√=7TeV collected by the ATLAS experiment at the Large Hadron Collider in 2011. The event selection requires missing transverse momentum, no isolated electrons or muons, and from ≥6 to ≥9 jets. No evidence is found for physics beyond the Standard Model. The results are interpreted in the context of a MSUGRA/CMSSM supersymmetric model, where, for large universal scalar mass m 0, gluino masses smaller than 840 GeV are excluded at the 95% confidence level, extending previously published limits. Within a simplified model containing only a gluino octet and a neutralino, gluino masses smaller than 870 GeV are similarly excluded for neutralino masses below 100 GeV

Inclusive search for same-sign dilepton signatures in pp collisions at root s=7 TeV with the ATLAS detector

An inclusive search is presented for new physics in events with two isolated leptons (e or mu) having the same electric charge. The data are selected from events collected from p p collisions at root s = 7 TeV by the ATLAS detector and correspond to an integrated luminosity of 34 pb(-1). The spectra in dilepton invariant mass, missing transverse momentum and jet multiplicity are presented and compared to Standard Model predictions. In this event sample, no evidence is found for contributions beyond those of the Standard Model. Limits are set on the cross-section in a fiducial region for new sources of same-sign high-mass dilepton events in the ee, e mu and mu mu channels. Four models predicting same-sign dilepton signals are constrained: two descriptions of Majorana neutrinos, a cascade topology similar to supersymmetry or universal extra dimensions, and fourth generation d-type quarks. Assuming a new physics scale of 1 TeV, Majorana neutrinos produced by an effective operator V with masses below 460 GeV are excluded at 95% confidence level. A lower limit of 290 GeV is set at 95% confidence level on the mass of fourth generation d-type quarks

Measurement of the top quark-pair production cross section with ATLAS in pp collisions at \sqrt{s}=7\TeV

A measurement of the production cross-section for top quark pairs(\ttbar) in $pp$ collisions at \sqrt{s}=7 \TeV is presented using data recorded with the ATLAS detector at the Large Hadron Collider. Events are selected in two different topologies: single lepton (electron $e$ or muon $\mu$) with large missing transverse energy and at least four jets, and dilepton ($ee$, $\mu\mu$ or $e\mu$) with large missing transverse energy and at least two jets. In a data sample of 2.9 pb-1, 37 candidate events are observed in the single-lepton topology and 9 events in the dilepton topology. The corresponding expected backgrounds from non-\ttbar Standard Model processes are estimated using data-driven methods and determined to be $12.2 \pm 3.9$ events and $2.5 \pm 0.6$ events, respectively. The kinematic properties of the selected events are consistent with SM \ttbar production. The inclusive top quark pair production cross-section is measured to be \sigmattbar=145 \pm 31 ^{+42}_{-27} pb where the first uncertainty is statistical and the second systematic. The measurement agrees with perturbative QCD calculations.Comment: 30 pages plus author list (50 pages total), 9 figures, 11 tables, CERN-PH number and final journal adde