CMS b-Tagging Two classes of discriminators w/ 2-3 operating points each: Track counting: requires minimum number of tracks (2 or 3) exceeding some IP significance Simple secondary vertex: requires SV with 2 or 3 tracks, discriminant based on 3D flight distance Loose operating point for track counting has ~80% efficiency, ~10% mistag rate Efficiency well-modeled to 5% level.