A data driven estimation of the $t\bar t$ background for the measurement of the $W$ production cross section in association with jets with the ATLAS detector

This report presents a data driven estimation of the $t\bar t$ background for the measurement of the $W$ production cross section in association with jets. The data set which was accumulated from proton-proton collisions at a center of mass energy of $\sqrt{s} = 8$ TeV at the Large Hadron Collider in 2012 is used for the measurement. The total number of $t\bar t$ events as a function of the jet multiplicity in the signal region of the muon channel is determined by performing a maximum likelihood fit of a $t\bar t$ template together with signal and other background Monte Carlo simulations to the data. Eight different $t\bar t$ templates obtained from data have been tested. Furthermore the method determines a shape estimate of the $t\bar t$ background for some kinematic distributions. The results are compared to the prediction of the next-to-leading-order Monte Carlo generator POWHEG.