Measurement of the Top Quark Pair Production Cross Section and an in-situ B-tagging efficiency Calibration with ATLAS in $pp$ collisions at $sqrt{s} = 7$ TeV in Dilepton Final States

We present a measurement of the top anti-top quark (t¯t) production cross section in the dilepton final states from proton-proton collisions at a center of mass energy at 7 TeV at the LHC. A b-tagging algorithm based on tracks displaced from the event interaction vertex is applied to identify bottom quark jets from top quark decay and reject background events. Given the relatively pure sample of bottom quark jets in t¯t dilepton final states, a new technique to measure in-situ the b-tagging efficiency is introduced that uses the distribution of the number of observed b-tagged jets. We present results with data collected at the ATLAS detector in 2010 with an integrated luminosity of 35 pb−1. The measured t¯t cross section is 176+22−21(stat.) +20−20(syst.) ± 6(lum.) pb in the dilepton channel. We will also discuss the future prospects of this measurement.