Measurement of the top quark pair production cross section in $pp$ collisions at 7 TeV center of mass energy using electrns, jets and $b$-tags

We present a measurement of top quark pair production cross section using 36 pb$^{-1}$ of data collected by the CMS detector in pp collisions at a center-of-mass energy of 7~TeV. We select events containing one isolated electron, high missing transverse energy and at least three energetic jets. Data driven methods are used to estimate the amount of QCD and $W+$jets in our preselected data, and these backgrounds are then suppressed through the identification of the $b$-jets by reconstructing secondary vertices. The cross section is extracted from the excess of tagged events with at least three jets over the background prediction.