Experimental Limits On Extra-Z Bosons From E+E- Annihilation Data With The Venus Detector At Square-Root-S=50-64 Gev

Abstract We have tested extra Z models in the reactions e+e−→μ+μ−, τ+τ− and hadrons in the energy range 50 s GeV using the VENUS detector at the TRISTAN e+e− storage ring. Our data are in good agreement with the standard model prediction ( χ 2 N Df = 2.9 31 ) ). We have obtained 90% confidence-level lower limits of 105, 125 and 231 GeV for the masses of ZΨ, Zη and Zχ bosons which are expected from the E6 grand unified theory. We also place a 90% confidence-level lower limit of 426 GeV for the mass of an extra-Z boson whose couplings to quarks and leptons are assumed to be the same as those for the standard Z boson. Our results exceed the previous experimental limits from the p p collider experiments, although there have been some combined analyses reporting the limits better than those obtained in the present analysis.