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A measurement of the production cross-section for top quark pairs (t (t) over bar) in pp collisions at root s = 7 TeV is presented using data recorded with the ATLAS detector at the Large Hadron Collider. Events are selected in the single lepton topology by requiring an electron or muon, large missing transverse momentum and at least three jets. With a data sample of 35 pb(-1), two different multivariate methods, one of which uses b-quark jet identification while the other does not, use kinematic variables to obtain cross-section measurements of sigma(t (t) over bar) = 187 +/- 11(stat.)(-17)(+18)(syst.) +/- 6(lumi.) pb and sigma(t (t) over bar) = 173 +/- 17(stat.)(-16)(+18)(syst.) +/- 6(lumi.) pb respectively. The two measurements are in agreement with each other and with QCD calculations. The first measurement has a better a priori sensitivity and constitutes the main result of this Letter. (c) 2012 CERN. Published by Elsevier B.V. All rights reserved

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Search for long-lived, heavy particles in final states with a muon and multi-track displaced vertex in proton-proton collisions at √ s = 7 TeV with the ATLAS detector ✩ .ATLAS Collaboration a r t i c l e i n f o a b s t r a c t Many extensions of the Standard Model posit the existence of heavy particles with long lifetimes. In this Letter, results are presented of a search for events containing one or more such particles, which decay at a significant distance from their production point, using a final state containing charged hadrons and an associated muon. This analysis uses a data sample of proton-proton collisions at √ s = 7 TeV corresponding to an integrated luminosity of 4.4 fb −1 collected in 2011 by the ATLAS detector operating at the Large Hadron Collider. Results are interpreted in the context of R-parity violating supersymmetric scenarios.No events in the signal region are observed and limits are set on the production cross section for pair production of supersymmetric particles, multiplied by the square of the branching fraction for a neutralino to decay to charged hadrons and a muon, based on the scenario where both of the produced supersymmetric particles give rise to neutralinos that decay in this way. However, since the search strategy is based on triggering on and reconstructing the decay products of individual long-lived particles, irrespective of the rest of the event, these limits can easily be reinterpreted in scenarios with different numbers of long-lived particles per event. The limits are presented as a function of neutralino lifetime, and for a range of squark and neutralino masses. © 2013 CERN. Published by Elsevier B.V. All rights reserved. collisions [18], who also study decays to a bb pair [19], and at LEP [20]. The result reported here improves on the previous AT-LAS search for this signature [16] in several ways. The dataset is around 100 times larger, corresponding to an integrated luminosity of 4.4 fb −1 [21]. Furthermore, the signal efficiency is increased by improving the reconstruction efficiency for reconstructing tracks 1 Following submission of our Letter, this paper was submitted addressing the same physics, but for a different final state. 0370-2693/