Measurement of the $b$-jet identification efficiency for high transverse momentum jets in $t\bar{t}$ events in the lepton + jets channel with the ATLAS detector using Run 2 data

The identification of jets containing $b$-hadrons is a crucial ingredient for many analyses of the ATLAS experiment physics programme. This document presents a new method to calibrate the efficiency of identifying such jets at high transverse momentum ($p_\text{T}$), extending the coverage of existing calibrations by using high-$p_\text{T}$ one-lepton $t\bar{t}$ events. The proton-proton collision data recorded between 2015 and 2018 by the ATLAS detector at the Large Hadron Collider are used, representing an integrated luminosity of 139 fb$^{-1}$. The method, based on a likelihood-fit approach, relies on efficiently selecting high-$p_\text{T}$ $t\bar{t}$ events by the identification of a large-radius $R=1.0$ jet, and the subsequent construction of an event-level variable independent of the $b$-tagging information, the flavour composition and the $b$-jet identification efficiency to be constrained simultaneously. The results improve and extend the previous calibration at high-$p_\text{T}$, resulting into a precision of $\approx$10% for jets with transverse momenta between 500 and 1000 GeV.