Study of exclusive charmless semileptonic B decays and extraction of |Vub| at CLEO

We have studied semileptonic B decay to the exclusive charmless states π, ρ/ω, η and η′ using the full 15.5fb-1 CLEO Υ(4S) sample, with measurements performed in subregions of phase space to minimize dependence on a priori knowledge of the form factors involved. We find total branching fractions B(B0→π-+ν)=(1.37±0.15stat±0. 11sys)×10-4 and B(B0→ρ-+ν)=(2.93±0.37stat±0. 37sys)×10-4. We find evidence for B+→η′+ν, with B(B+→η′+ν)=(2.66±±0.80stat±0.56sys) ×10-4 and 1.20×10-4<B(B+→η′+ν)<4. 46×10-4 (90% CL). We also limit B(B+→η+ν)<1.01×10-4 (90% CL). By combining our B→πν information with unquenched lattice calculations, we find |Vub|=(3.6±0.4stat±0.2sys-0.4thy+0.6) ×10-3.