E+E--]TAU+TAU- AT THE THRESHOLD AND BEYOND

The excitation curve for the tau+tau- production in electron positron annihilation near the threshold is revisited with the aim of updating and extending a previous work. We find that the corrections of the rel ative magnitude O(alpha) near the threshold are significantly contribu ted by the radiative modification of the Coulomb interaction between t he tau leptons. The interpolation between the Coulomb effects at the t hreshold and the relativistic effects at higher energies is considered and the resulting formula is argued to have relative accuracy up to, but not including, terms of the order of alpha2 at any velocity of the tau leptons.