Z-Decays to b Quarks and the Higgs Boson Mass

Abstract

A model independent analysis of the most recent averages of precision electroweak data from LEP and SLD finds a 3$\sigma$ deviation of the parameter $A_b$ from the Standard Model prediction. The fitted value of $m_H$ shows a strong dependence on the inclusion or exclusion of b quark data, and the Standard Model fits have poor confidence levels of a few percent when the latter are included. The good fits obtained to lepton data, c quark data and the directly measured top quark mass, give $m_t = 171.2_{-3.8}^{+3.7}$ GeV and indicate that the Higgs boson mass is most likely less than 200 GeV.