Identification of $b$-jets in boosted and dense jet event topologies

This talk presents the calibration of various ATLAS $b$-tagging algorithms using reconstructed $t \bar{t}$ candidate events in the final state of one charged lepton, missing transverse momentum, and at least four jets, in the ATLAS $\sqrt{s}=8~\mathrm{TeV}$ $pp$ collision data sample. Expanding on previous $b$-tagging calibration studies, the $b$-tagging efficiencies are measured not only as a function of the transverse momentum or the pseudorapidity of the jets, but also as a function of quantities that are sensitive to close-by jet activity. The results measured in data are in good agreement with the predictions from simulation.