Evidence for new-flavor production at the (4S)

An enhancement has been observed in the inclusive cross section for direct single electrons produced in e/sup +/e/sup -/ annihilation at the UPSILON(4S). This is interpreted as evidence for a new weakly decaying particle, the B meson. A branching ratio for B..-->..Xe..nu.. of (13 +- 3( +- 3))% is inferred, where the first set of errors is statistical and the estimated systematic error is enclosed in parentheses.