Supersymmetry and R_b in the light of LEP 1.5

Abstract

We re-examine the possible magnitude of the supersymmetric contribution to $R_b\equiv \Gamma (Z^0\to \bar{b}b)/\Gamma (Z^0\to \mathrm{all})$ in the light of the constraints imposed by the absence of light charginos at LEP~1.5, implementing also other available phenomenological constraints. We find the supersymmetric contribution to be $R_b^{\mathrm{susy}}<0.0017$, and discuss the extent to which this upper bound could be strengthened by future constraints on the chargino and top-squark masses. Such values of $R_b^{\mathrm{susy}}$ tend to disfavor a supersymmetry explanation of the apparent $R_b$ discrepancy.

Comments: 10 pages (LaTeX), 2 figures (uuencoded)