A Search for B+ --> tau+ nu Recoiling Against B- --> D0 l- nu X

Abstract

We present a search for the decay $B^{+}\to {\tau }^{+}{\nu }_{\tau }$ in $88.9\times 10^6$ ${\rm Y}(4S)$ decays recorded with the BABAR detector at the SLAC $B$-Factory. A sample of semi-exclusive, semi-leptonic B decays ($B^{-}\to D^0{\ell }^{-}\overline{{\nu }_{\ell }}X$), where $X$ is either a photon, ${\pi }^0$, or nothing, is used to identify the daughter particles that are associated with the other $B$ meson in each event. These particles are searched for evidence of a one-prong leptonic $B^{+}\to {\tau }^{+}{\nu }_{\tau }$ decay. For this data sample we set a preliminary upper limit on the branching fraction of $\mathcal{B}(B^{+}\to {\tau }^{+}{\nu }_{\tau })<4.9\times 10^{-4}$ at the 90% confidence level. This result is then combined with a statistically independent BABAR search for $B^{+}\to {\tau }^{+}{\nu }_{\tau }$ to give a combined preliminary limit of $\mathcal{B}(B^{+}\to {\tau }^{+}{\nu }_{\tau })<4.1\times 10^{-4}$.