Search for τ-→γμ- : a test of Lepton number conservation

A search for the lepton number violating decay of the τ lepton to the γμfinal state has been performed with the CLEO II detector at the Cornell e + e - storage ring CESR. In a data sample that corresponds to an integrated luminosity of 1.55 fb -1 , we observe no candidates in the signal region. We thus determine an upper limit of B(τ - →γμ - )<4.2×10 -6 at 90% confidence level