PRELIMINARY RESULTS FOR EXCLUSIVE b → uℓν DECAYS FROM CLEO

A preliminary analysis of exclusive b → uℓν decays to the final states π ∓ ℓ ± ν, π 0 ℓ ± ν, ρ ∓ ℓ ± ν, ρ 0 ℓ ± ν and ωℓ ± ν based on 2.2 × 10 6 B ¯ B decays collected at CLEO is presented. We have measured the first exclusive b → uℓν branching fraction B(B 0 → π − ℓ + ν) =), with the ISGW (WSB) model used for efficiency determination. A 90% C.L. upper limit on B(B 0 → ρ − ℓ + ν) similar to the previous CLEO limit is obtained. The ratio Γ(B 0 → ρ − ℓ + ν)/Γ(B 0 → π − ℓ + ν) < 3.4 at the 90% confidence level for both the ISGW and WSB models. This ratio provides some discrimination between form factor models.