Measurements ofRbwith impact parameters and displaced vertices

We present measurements of ${\mathit{R}}_{\mathit{b}}$ using the SLD at the SLC. The analyses use 2D and 3D impact parameter tags and a displaced 3D vertex tag which all exploit the small size and stability of the ${\mathit{e}}^{+}$ ${\mathit{e}}^{\mathrm{-}}$ interaction point and the precision 3D CCD pixel vertex detector to achieve high bb¯-tagging efficiencies and purities. The combined measurement yields ${\mathit{R}}_{\mathit{b}}$=0.229±0.011 and is consistent with standard model predictions. © 1996 The American Physical Society.