Measurement of the top quark cross-section in the single-lepton channel in $pp$ collisions at $sqrt{s} = 7$ TeV using kinematic fits and b-tagging information with the ATLAS Experiment

The measurement of the top-quark pair production cross-section is a powerful tool to test the Standard Model (SM) at a new energy. With the recent advances in theoretical calculations that led to predictions at a precision level of 10%, this measurement particularly provides a precision test of the theory of Quantum Chromodynamics. At the same time, the decays of top-quark pairs are phenomenologically similar to processes predicted by beyond-SM theories, thus representing an irreducible background that has to be studied thoroughly. In this first phase of data taking of the ATLAS detector, a copious process like $mathit{tar t}$ production can be also exploited to test the performance of the detector itself. The single-lepton channel, in which the $W$ boson produced in the decay of one top quark decays leptonically and the $W$ boson from the other top quark decays hadronically, currently provides the best trade-off between experimental accessibility, production rate and background contamination. The measurement of the $mathit{tar t}$ production cross-section in the single-lepton channel in pp collisions at a centre-of-mass energy $sqrt{mathrm{s}}$ =7 TeV is presented. The analysis is based on a multivariate discriminant distribution in 3, 4 and $ge$ 5 jet bins using three kinematic variables and b-tagging information. With a data sample of about 35 pb$^{-1}$ recorded by ATLAS in 2010 the inclusive top quark production cross-section is measured to be $sigma_{mathit{tar t}}$ = 186 $pm$ 10 (stat.)$^{+21}_{-20}$ (syst.) $pm$ 6 (lumi.) pb. This measurement is in agreement with theory predictions.