$b$-jet tagging calibration on $c$-jets containing $D^{*+}$ mesons

The $b$-jet tagging efficiency on jets containing charm hadrons ($c$-jets) has been measured using a sample of $D^{*+}$ mesons, reconstructed within a jet in the $D^{*+}\rightarrow D^0(\rightarrow K^- \pi^+)\pi^+$ final state. The measurement is based on 5~fb$^{-1}$ of data collected in 2011 by the ATLAS detector. The $b$-tagging efficiency on $c$-jets has been extracted by comparing the yield of $D^{*+}$ mesons before and after the tagging requirement. The contamination with $D^{*+}$ mesons that result from $b$-hadron decays has been measured with a fit to the $D^0$ pseudo-proper time distribution. The measurement of the $c$-tagging efficiency is provided in the form of jet $p_T$ and $\eta$ dependent scale factors that correct the $b$-tagging performance in simulation to that observed in data. The precision of the measurement depends on the tagging algorithm, operating point and jet $p_T$ bin. For the high-performance MV1 tagging algorithm at an operating point corresponding to a 70% $b$-tag efficiency in $t\overline{t}$ events, the total uncertainty ranges from 12% to 25%.