Search for exclusiveb→usemileptonic decays ofBmesons

Using a sample of 935 000 BB¯ pairs collected with the CLEO-II detector at the Cornell Electron Storage Ring, we have obtained upper limits on the branching ratios for the b→${\mathit{ul}}^{\mathrm{-}}$ν¯ processes ${\mathit{B}}^{\mathrm{-}}$→ω${\mathit{l}}^{\mathrm{-}}$ν¯, ${\mathit{B}}^{\mathrm{-}}$→${\mathrm{\rho }}^0$ ${\mathit{l}}^{\mathrm{-}}$ν¯, and B${\mathrm{¯}}^0$→${\mathrm{\rho }}^{+}$ ${\mathit{l}}^{\mathrm{-}}$ν¯. The combined result using the relationships among the widths for these three modes is B(${\mathit{B}}^{\mathrm{-}}$→${\mathrm{\rho }}^0$ ${\mathit{l}}^{\mathrm{-}}$ν¯)<(1.6–2.7)×${10}^{\mathrm{-}4}$ at 90% C.L., where the range of values is due to model dependence of the detection efficiencies. These measurements yield the limits ‖${\mathit{V}}_{\mathit{u}\mathit{b}}$/${\mathit{V}}_{\mathit{c}\mathit{b}}$‖<0.08–0.13.