PRECISE MEASUREMENT OF BHABHA SCATTERING AT A CENTER-OF-MASS ENERGY OF 57.77 GEV

Bhabha scattering at a center-of-mass energy of 57.77 GeV has been mea sured using the VENUS detector at KEK TRISTAN. The precision is better than 1% in scattering angle regions of \cos theta\less than or equal to 0.743 and 0.822 less than or equal to cos theta less than or equal to 0.968. A model-independent scattering-angle distribution is extract ed from the measurement. The distribution is in good agreement with th e prediction of the standard electroweak theory. The sensitivity to un derlying theories is examined, after unfolding the photon-radiation ef fect. The q(2) dependence of the photon vacuum polarization, frequentl y interpreted as a running of the QED fine-structure constant, is dire ctly observed with a significance of three standard deviations. The Z( 0) exchange effect is clearly seen when the distribution is compared w ith the prediction from QED (photon exchanges only). The agreement wit h the standard theory leads us to constraints on extensions of the sta ndard theory. In all quantitative discussions, correlations in the sys tematic error between angular bins are taken into account by employing an error matrix technique.