Cross-Sections And Charge Asymmetries For E+E--]Mu+Mu- And E+E--]Tau+Tau-Reactions At Root-S=52-61.4 Gev

The processes e+e- --> mu+mu- and e+e- --> tau+tau- have been studied in the energy range square-root s = 52-61.4 GeV, using the TOPAZ detector at TRISTAN. From an integrated luminosity of L = 74.0 pb-1, lowest-order cross sections and forward-backward asymmetries are measured to be [sigma(mumu)] = 25.4 +/- 0.9 +/- 1.2 pb, [A(mumu)] = (-32.2 +/- 3.1 +/- 1.1)%, [sigma(tautau)] = 27.1 +/- 1.1 +/- 1.2 pb, [A(tautau)] = (-33.9 +/- 4.9 +/- 1.0)%, at an average energy of [square-root s] = 57.87 GeV. From the measured asymmetry we derive axial vector couplings of a(e)a(mu) = 0.96 +/- 0.09 +/- 0.01, and a(e)a(tau) = 1.01 +/- 0.14 +/- 0.01. These results are consistent with the standard model expectations. Lower limits in the range 2-5 TeV (95% CL) are placed on compositeness scale parameters for leptons.