Performance studies of $b$-tagging algorithms using top quark pair production in $pp$ collisions at the center of mass energy 7 TeV with the ATLAS experiment

$b$-tagging algorithms are calibrated with $tar{t}$ events for the first time with early data in the ATLAS experiment. Compared to di-jet events that have been used for $b$-tagging calibrations, $tar{t}$ events provide closer signature to most of the important signals in the experiment. The higher multiplicity of jets, higher $p_{T}$, high purity of $tar{t}$ event sample with two $b$-jets per events are very attractive aspects of $tar{t}$ events. Also, the high $tar{t}$ production rate in the experiment enables calibrations already with 35 pb$^{-1}$. Two successful first attempts are presented in EPS 2011.