Preliminary Results For Exclusive $b\to u\ell\nu$ Decays From CLEO

Abstract

A preliminary analysis of exclusive $\btou$ decays to the final states $\pi^\pm\ell\nu$, $\pi^0\ell\nu$, $\rho^\pm\ell\nu$, $\rho^0\ell\nu$\ and $\omega\ell\nu$ based on $2.2\e{6}$ $\bbar$ decays collected at CLEO is presented. We have measured the first exclusive $\btou$ branching fraction $\bbpi=[1.19\pm0.41\pm0.21\pm0.19]\e{-4}$ ($[1.70\pm0.51\pm0.31\pm0.27]\e{-4}$), with the ISGW (WSB) model used for efficiency determination. A 90\% C.L. upper limit on $\bbrho$ similar to the previous CLEO limit is obtained. The ratio $\gamrho/\gampi<3.4$ at the 90\% confidence level for both the ISGW and WSB models. This ratio provides some discrimination between form factor models.