Measurement of the Mistag Rate with 5 fb$^{−1}$ of Data Collected by the ATLAS Detector

The mistag rates of several b-tagging algorithms have been measured with two complementary methods using data from the ATLAS detector. The measurements use inclusive jet samples selected from 5 fb$^{-1}$ of data collected in 2011. The first method uses the invariant mass spectrum of tracks associated with reconstructed secondary vertices to separate light and heavy-flavour jets, and the other is based on the rate at which secondary vertices with negative decay length, or tracks with negative impact parameter, are present in the data. The measurements of the mistag rate are provided in the form of jet-$p_{\rm T}$ and $\eta$ dependent scale factors that correct the $b$-tagging performance in simulation to that observed in data. Good consistency is observed between the results of the two methods. The uncertainties range from less than 10% to more than 100% for the tightest operating points.