Measurement of the branching fraction for $Υ(1S) \to τ^+ τ^-$

Abstract

We have studied the leptonic decay of the $Υ(1S)$ resonance into tau pairs using the CLEO II detector. A clean sample of tau pair events is identified via events containing two charged particles where exactly one of the particles is an identified electron. We find $B(Υ(1S) \to τ^+ τ^-) = (2.61~\pm~0.12~{+0.09\atop{-0.13}})%$. The result is consistent with expectations from lepton universality.