Search for exclusive b→u semileptonic decays of B mesons

Using a sample of 935000 BB pairs collected with the CLEO-II detector at the Cornell Storage Ring, we have obtained upper limits on the branching ratios for the b→ul - υ#58 processes B - →ωl - υ#58, B - →ρ 0 l - υ#58, and B 0 →ρ + l - υ#58. The combined result using the relationships among the widths for these three modes is B(B - →ρ 0 l - υ#58)<(1.6-2.7)×10 -4 at 90% C. L., where the range of value to model dependence of the detection efficiencies. These measurements yield the limits |V ub /V cb |<0.08-0.13