Soft $b$-hadron tagging with the ATLAS detector

The identification of $b$-hadrons at low $p_T$ can play a crucial role in a variety of analyses where soft $b$-hadrons are produced by physics beyond the Standard Model such as compressed SUSY searches for stop/sbottom production, and also in analyses that require heavy flavour jet vetos. Such $b$-hadron identification is a particularly challenging task, owing to the relatively short decay length of such $b$-hadrons and difficulties identifying hadronic jets, and current flavour tagging algorithms are not tuned to identify such $b$-hadron decays. This article presents new developments for soft $b$-hadron tagging techniques based either on the presence of jets composed only of charged tracks, or on the identification of secondary vertices from the $b$-hadron decay without requiring the presence of a jet. The techniques are described and their performance is reviewed.