Production and properties of the τ-lepton in e+e− annihilation at C.M. energies from 12 to 31.6 GeV

We have observed τ production in e+e− annihilation at centre-of-mass energies between 12 and 31.6 GeV with cross sections in agreement with the QED τ-pair cross section. Branching ratios for τ decay have been measured and are consistent with the world averages. We have determined the cutoff parameters of QED Λ+ (Λ−) to be > 73 GeV (82 GeV) and have obtained an upper limit on the τ lifetime of 1.4 × 10−12 s(95% CL).