Comprehensive analysis of data pertaining to the weak neutral current and the intermediate-vector-boson masses

The results of a comprehensive analysis of existing data on the weak neutral current and the W and Z masses are presented. The principal results are the following. (a) There is no evidence for any deviation from the standard model. (b) A global fit to all data yields sin²{{{θ}}}W≡1-{M}W²/MZ{}²=0.230±0.0048, where this error and all others given here include full statistical, systematic, and theoretical uncertainties (computed assuming three fermion families,{m}ₜ≤100 GeV, and{M}H≤1 TeV). (c) Allowing ρ≡{M}W²/(MZ{}²cos²{{{θ}}}W$) as well as ${sin}²θW to vary one obtains sin²{{{θ}}}W$=0.229±{}0.0064 and {ρ}=0.998±{}0.0086. This implies 90%-confidence-level (C.L.) upper limits of 0.047 and 0.081 for the vacuum expectation values (relative to those of Higgs doublets) for Higgs triplets with weak hypercharge of 0 and ±{}1, respectively. (d) The parameter δW{≡}{Δ}r-{Δ}s²(1-{Δ}r)/sin²{{{θ}}}⁰$, which is a measure of the radiative corrections relating deep-inelastic neutrino scattering, the W and Z masses, and muon decay, is determined to be 0.112±{}0.037. This is consistent with the value δW=0.106 expected for mₜ=45 GeV and MH=100 GeV and establishes the existence of radiative corrections at the 3{σ} level. (e) The radiative corrections are sensitive to isospin breaking associated with a large mₜ.Assuming no deviation from the standard model, consistency of the various reactions requires mₜ180 GeV at 90% C.L. for MH{≤}100 GeV, with a slightly weaker limit for larger MH. Similar results hold for the mass splittings between fourth-generation quarks or leptons. (f) Most of the parameters in model-independent fits to {ν}q, {ν}e, eq, and e⁺{e}^{{{-}}}$ processes are now determined uniquely and precisely. (g) Limits are given on the masses and mixing angles of additional Z bosons expected in popular models. For theoretically expected coupling constants one finds that the neutral-current constraints are usually more stringent than the direct-production limits from the CERN Sp{}pS collider, but nevertheless masses as low as 120--300 GeV are typically allowed. (h) The implications of these results for grand unification are discussed. sin²{{{θ}}}Wis ≥2.5 standard deviations above the prediction of minimal SU(5) and similar models for all{m}ₜ$. It is closer to the prediction of simple supersymmetric grand unified theories but is still somewhat low. (i) The dominant theoretical uncertainty (the charm-quark threshold in deep-inelastic charged-current scattering) is considered in some detail.