Vertexing for b-Tagging

Tagging of $b$-quark jets, ``$b$-tagging'', is an important ingredient for Standard Model analyses as well as for searches for new physics. A property of $b$-quark jets exploited by $b$-tagging algorithms is the presence of secondary $b$- and $c$-hadron decay vertices. In this note, methods for the explicit reconstruction of secondary and/or tertiary decay vertices of $b$- and $c$-hadron decays are presented. The performance of the secondary vertex based $b$-tagging algorithms and the dependences on the event topology and jet kinematics are studied. The efficient reconstruction of the primary interaction vertex is also crucial for $b$-tagging, especially in the presence of pile-up interaction vertices at LHC luminosity. The ATLAS primary vertex reconstruction strategies and performances are presented in this note as well.