A Search for B --> tau nu Recoiling against B --> D*0 l nu

Abstract

We present a search for the decay $B^{+}\to \ddot{I}{„}^{+}\hat{I}{½}_{\ddot{I}}„$ in $124.1\times 10^6$ $\hat{I}\yen (4S)$ decays recorded with the $BABAR$ detector at the SLAC PEP-II $B$-Factory. A sample of events with one reconstructed exclusive semi-leptonic B decay ($B^{-}\to D^{\ast 0}{\ell }^{-}\bar{\hat{I}}{½}_{\ell }$) is selected, and in the recoil a search for $B^{+}\to \ddot{I}{„}^{+}\hat{I}{½}_{\ddot{I}}„$ signal is performed. The $\ddot{I}„$ is identified in the following channels: $\ddot{I}{„}^{+}\to e^{+}\hat{I}{½}_e\bar{\hat{I}}{½}_{\ddot{I}}„$, $\ddot{I}{„}^{+}\to \hat{I}{¼}^{+}\hat{I}{½}_{\hat{I}}¼\bar{\hat{I}}{½}_{\ddot{I}}„$, $\ddot{I}{„}^{+}\to \ddot{I}{€}^{+}\bar{\hat{I}}{½}_{\ddot{I}}„$, $\ddot{I}{„}^{+}\to \ddot{I}{€}^{+}\ddot{I}{€}^0\bar{\hat{I}}{½}_{\ddot{I}}„$, $\ddot{I}{„}^{+}\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}\ddot{I}{€}^{+}\bar{\hat{I}}{½}_{\ddot{I}}„$. We find no evidence of signal, and we set a preliminary upper limit on the branching fraction of $\mathcal{B}(B^{+}\to \ddot{I}{„}^{+}\hat{I}{½}_{\ddot{I}}„)<4.3\times 10^{-4}$ at the 90% confidence level (CL). This result is then combined with a statistically independent $BABAR$ search for $B^{+}\to \ddot{I}{„}^{+}\hat{I}{½}_{\ddot{I}}„$ to give a combined preliminary limit of $\mathcal{B}(B^{+}\to \ddot{I}{„}^{+}\hat{I}{½}_{\ddot{I}}„)<3.3\times 10^{-4}$ at 90% CL.

25 pages, 12 postscript figues, submitted to ICHEP2004