MEASUREMENTS OF CROSS-SECTION AND CHARGE ASYMMETRY FOR E--]MU+MU- ANDE+E--]TAU+TAU- AT ROOT-S=57.8 GEV(E)

With data corresponding to 142 pb-1 accumulated at square-root s = 57. 8 GeV by the AMY detector at TRISTAN we measure the cross section of t he reactions e+e- --> mu+mu- and e+e- --> tau+tau- and the asymmetry i n the angular distributions. For the lowest order cross section we obt ain sigma(mumu) = 27.54 +/- 0.65 +/- 0.95 pb and sigma(tautau) = 28.27 +/- 0.87 +/- 0.69 pb, and for the forward-backward asymmetry, A(mumu) = -0.303 +/- 0.027 +/- 0.008 and A(tautau) = -0.291 +/- 0.040 +/- 0.0 19. These measurements agree with the standard model. Assuming e-mu-ta u universality we extract the vector and axial coupling constants \gv\ = 0.00 +/- 0.09 and \g(A)\ = 0.476 +/- 0.024. A fit of the data to co mposite models places lower bounds (95% confidence level) on the compo siteness scale of 2-4 TeV.