Calibration of the ATLAS $b$-tagging algorithm in $t\bar{t}$ semi-leptonic events

The calibration of the ATLAS $b$-tagging algorithm in environments characterised by large jet multiplicity is presented. The calibration uses reconstructed $t\bar{t}$ candidate events collected by the ATLAS detector in proton-proton collisions at $13\,$TeV, with a final state containing one charged lepton, missing transverse momentum and at least four jets. The $b$-tagging efficiencies are measured as a function of the transverse momentum and the pseudo-rapidity of the jets. The results for the data-to-simulation scale factors are presented in an extended tranverse momentum region compared to $b$-tagging calibrations based on dileptonic $t\bar{t}$ events.