IMPLICATIONS OF HIGH-PRECISION EXPERIMENTS AND THE CDF TOP-QUARK CANDIDATES

We discuss the consequences of recent experimental results from CDF, SLC, CERN LEP, and elsewhere for the standard model and for new physics, A global fit to all indirect precision data yields mt=175±11-19+17 GeV, sin2θMS̄=0.2317(3)(2), and αs=0.127(5)(2), where the central values are for MH=300 GeV and the second uncertainties are for MH→1000 GeV (+) and 60 GeV (-). The mt value is in remarkable agreement with the value mt value is in remarkable agreement with the value mt=174±16 GeV suggested by the CDF candidate events. There is a slight preference for a light Higgs boson with MH<730 (880) GeV at 95% C.L. if the CDF mt value is (not) included. The sensitivity is, however, due almost entirely to the anomalously large observed values for the Z→bb̄ width and left-right asymmetry. The value of αs (from the line shape) is clean theoretically assuming the standard model, but is sensitive to the presence of new physics contributions to the Z→bb̄ vertex. Allowing a vertex correction δbbnew one obtains the significantly lower value αs=0.111±0.009, in better agreement with low energy determinations, and δbbnew=0.023±0.011. There is now enough data to perform more general fits to parameters describing new physics effects and to separate these from mt and MH. Allowing the parameter ρ0, which describes sources of SU(2) breaking beyond the standard model, to be free one finds ρ0=1.0012±0.0017±0.0017, remarkably close to unity. One can also separate the new physics contributions to the oblique parameters Snew, Tnew, and Unew, which all take values consistent with zero. The effects of supersymmetry on the determination of the standard model parameters are discussed. © 1995 The American Physical Society.