IMPLICATIONS OF GAMMA(ZETA-]B(B)OVER-BAR) FOR SUPERSYMMETRY SEARCHES AND MODEL-BUILDING

Assuming that the actual values of M(t) at FNAL and of Gamma(Z --> b ( b) over bar)/Gamma(Z --> hadrons) at LEP are within their current 1 si gma reported ranges, we present a No-Lose Theorem for superpartner sea rches at LEP II and an upgraded Tevatron. We impose only two theoretic al assumptions: the Lagrangian is that of the Minimal Supersymmetric S tandard Model (MSSM) with arbitrary soft-breaking terms, and all coupl ings remain perturbative up to scales similar to 10(16) GeV; there are no assumptions about the soft supersymmetry breaking parameters, prot on decay, cosmology, etc. In particular, if the LEP and FNAL values ho ld up and supersymmetry is responsible for the discrepancy with the St andard Model prediction of Gamma(Z --> b (b) over bar), then we must h ave charginos and/or top squarks observable at the upgraded machines ( for LEP the superpartner threshold is below root= 140 GeV). Furthermor e, little deviation from the Standard Model is predicted within ''supe r-unified'' supersymmetry, so these models predict that the discrepanc y between experiment and the Standard Model prediction for Gamma(Z --> b (b) over bar) will fade with time. Finally, it appears to be extrem ely difficult to find any unified MSSM model, regardless of the form o f soft supersymmetry breaking, that can explain T(Z --> b (b) over bar ) for large tan beta; in particular, no model with t-b-tau Yukawa coup ling unification appears to be consistent with the experiments.