A Search for the Decay B+ --> tau+ nu_tau

Abstract

We search for the rare leptonic decay B+ --> tau+ nu_tau in a sample of 232x10^6 BBbar pairs collected with the BABAR detector at the SLAC PEP-II B-Factory. Signal events are selected by examining the properties of the B meson recoiling against the semileptonic decay B- --> D*0 l- nu_lbar. We find no evidence for a signal and set an upper limit on the branching fraction of BR(B+ --> tau+ nu_tau) < 2.8x10^{-4} at the 90% confidence level. We combine this result with a previous, statistically independent BABAR search for B+ --> tau+ nu_tau to give an upper limit of BR(B+ --> tau+ nu_tau) < 2.6x10^{-4} at the 90% confidence level.