Measurement of $b$-tagging Efficiency of $c$-jets in $t\bar{t}$ Events Using a Likelihood Approach with the ATLAS Detector

A new technique is presented to measure the rate at which charm jets are tagged as $b$-jets based on a data sample of single lepton $t\bar{t}$ events, where one of the $W$-bosons decays leptonically and the other decays to a $c$- and $s$-quark, or other quark pair combinations. The data sample was collected by the ATLAS detector at $\sqrt{s} = 13$ TeV in 2015 and 2016 and corresponds to an integrated luminosity of 36 fb$^{-1}$. A kinematic likelihood technique is used to assign jets to the corresponding $t\bar{t}$ decay products. A likelihood fit is used to extract the $c$-jet tagging efficiency from the pair of jets associated to $W$-boson decays. This new technique is used to calibrate the ATLAS MV2c10 $b$-tagging algorithm.