Measurement of the branching fraction for ${\rm Y}(1S)\to {\tau }^{+}{\tau }^{-}$

Abstract

We have studied the leptonic decay of the ${\rm Y}(1S)$ 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 $B({\rm Y}(1S)\to {\tau }^{+}{\tau }^{-})=(2.61\pm 0.12\genfrac{}{}{0ex}{}{+0.09}{-0.13})$. The result is consistent with expectations from lepton universality.

9 pages, RevTeX, two Postscript figures available upon request, CLNS 94/1297, CLEO 94-20 (submitted to Physics Letters B)