Z'-bosons in supersymmetric E6 models confront electroweak data

We study constraints on additional Z'-bosons predicted in the supersymmetric (SUSY) E6 models by using the updated results of electroweak experiments - Z-pole experiments, mW measurements and low-energy neutral current (LENC) experiments. We find that the effects of Z-Z' mixing are parametrized by (i) a tree-level contribution to the T-parameter, (ii) the effective Z-Z' mass mixing angle anti ξ. In addition, the effect of the direct exchange of the heavier mass eigenstate Z2 in the LENC processes is parametrized by (iii) a contact term gE2/c2χmZ22. We give the theoretical predictions for the observables in the electroweak experiments together with the standard model radiative corrections. Constraints on Tnew and anti ξ from the Z-pole and mW experiments and those on gE2/c2χmZ22 from the LENC experiments are separately shown. Impacts of the kinetic mixing between the U(1)Y and U(1)' gauge bosons on the χ2-analysis are studied. We show the 95% CL lower mass limit of Z2 as a function of the effective Z-Z' mixing parameter ζ, a combination of the mass and kinetic mixings. A theoretical prediction on ζ and gE is given for the χ-, ψ-, η- and ν-models by assuming the minimal particle content of the SUSY E6 models. In a certain region of the parameter space, the Z2-boson mass in the detectable range of LHC is still allowed. (orig.)