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 ${\sin }^2$${\mathrm{\theta }}_{\mathrm{W}}$≡1-${\mathrm{M}}_{\mathrm{W}}$${\mathrm{}}^2$/${\mathrm{M}}_{\mathrm{Z}}$${\mathrm{}}^2$=0.230±0.0048, where this error and all others given here include full statistical, systematic, and theoretical uncertainties (computed assuming three fermion families, $m_t$≤100 GeV, and $M_H$≤1 TeV). (c) Allowing ρ≡$M_W$${\mathrm{}}^2$/($M_Z$${}^2$${\cos }^2$${\mathrm{\theta }}_{\mathrm{W}}$) as well as ${\sin }^2$${\mathrm{\theta }}_{\mathrm{W}}$ to vary one obtains ${\sin }^2$${\mathrm{\theta }}_{\mathrm{W}}$=0.229±0.0064 and ρ=0.998±0.0086. This implies 90%-confidence-level (C.L.) upper limits of 0.047 and 0.081 for the vacuum expectation values (relative to those of Higgs doublets) for Higgs triplets with weak hypercharge of 0 and ±1, respectively. (d) The parameter ${\delta }_W$≡Δr-Δ$s^2$(1-Δr)/${\sin }^2$${\mathrm{\theta }}^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 ${\delta }_W$=0.106 expected for $m_t$=45 GeV and $M_H$=100 GeV and establishes the existence of radiative corrections at the 3σ level. (e) The radiative corrections are sensitive to isospin breaking associated with a large $m_t$.

Assuming no deviation from the standard model, consistency of the various reactions requires $m_t$<180 GeV at 90% C.L. for $M_H$≤100 GeV, with a slightly weaker limit for larger $M_H$. Similar results hold for the mass splittings between fourth-generation quarks or leptons. (f) Most of the parameters in model-independent fits to νq, νe, eq, and $e^{+}$$e^{\mathrm{-}}$ processes are now determined uniquely and precisely. (g) Limits are given on the masses and mixing angles of additional Z bosons expected in popular models. For theoretically expected coupling constants one finds that the neutral-current constraints are usually more stringent than the direct-production limits from the CERN Sp¯pS collider, but nevertheless masses as low as 120–300 GeV are typically allowed. (h) The implications of these results for grand unification are discussed. ${\sin }^2$${\mathrm{\theta }}_{\mathrm{W}}$ is ≥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.