Production cross section and topological decay branching fractions of the τ lepton

Abstract

We report new measurements of the production cross section for the reaction e(+)e(−)→τ(+)τ(−) at s√=29 GeV, as well as the topological decay branching fractions of the τ lepton. The data were taken with the High Resolution Spectrometer at the SLAC e(+)e(−) colliding-beam facility PEP. The measured cross section yields Rττ=1.044±0.014±0.030 [where the first (second) error is statistical (systematic)], consistent with QED and corresponding to QED cutoff parameters of Λ+>129 GeV and Λ−>284 GeV at the 95% C.L. The fractions of τ decays into one and three charged particles are B1=0.864±0.003±0.003 and B3=0.135±0.003±0.003.