Measurement of the Z -> tau tau cross section with the ATLAS detector

The Z→ττ cross section is measured with the ATLAS experiment at the LHC in four different final states determined by the decay modes of the τ leptons: muon-hadron, electron-hadron, electron-muon, and muon-muon. The analysis is based on a data sample corresponding to an integrated luminosity of 36pb-1, at a proton-proton center-of-mass energy of √s=7TeV. Cross sections are measured separately for each final state in fiducial regions of high detector acceptance, as well as in the full phase space, over the mass region 66-116 GeV. The individual cross sections are combined and the product of the total Z production cross section and Z→ττ branching fraction is measured to be 0.97±0.07(stat)±0.06(syst)±0.03(lumi)nb, in agreement with next-to-next-to-leading order calculations. © 2011 CERN

Search for Contact Interactions in Dimuon Events from pp Collisions at s=7TeV\sqrt{s} = 7 TeV with the ATLAS Detector

A search for contact interactions has been performed using dimuon events recorded with the ATLAS detector in proton-proton collisions at sqrt(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 mumuqq contact interactions.Comment: 5 pages plus author list (18 pages total), 2 figures, 2 tables, submitted to Phys. Rev. D Rapid Communication

Search for a Heavy Particle Decaying into an Electron and a Muon with the ATLAS Detector in root s=7 TeV pp collisions at the LHC

This Letter presents the first search for a heavy particle decaying into an e(+/-)mu(-/+) final state in root s = 7 TeV pp collisions at the LHC. The data were recorded by the ATLAS detector during 2010 and correspond to a total integrated luminosity of 35 pb(-1). No excess above the standard model background expectation is observed. Exclusions at 95% confidence level are placed on two representative models. In an R-parity violating supersymmetric model, tau sneutrinos with a mass below 0.75 TeV are excluded, assuming all R-parity violating couplings are zero except lambda(311)' = 0.11 and lambda(312) = 0.07. In a lepton flavor violating model, a Z'-like vector boson with masses of 0.70-1.00 TeV and corresponding cross sections times branching ratios of 0.175-0.183 pb is excluded. These results extend to higher mass R-parity violating sneutrinos and lepton flavor violating Z's than previous constraints from the Tevatron