Study of the q2 dependence of B→πlν and of B→ρ(ω)lν and extraction of |Vub|

We report on determinations of |V_ub| resulting from studies of the branching fraction and q² distributions in exclusive semileptonic B decays that proceed via the b→u transition. Our data set consists of the 9.7×10⁶ BB¯ meson pairs collected at the Υ(4S) resonance with the CLEO II detector. We measure B(B⁰→π^-l⁺ν)=(1.33±0.18±0.11±0.01±0.07)×10^-4 and B(B⁰→ρ^-l⁺ν)=(2.17±0.34^+0.47_-0.54±0.41±0.01)×10^-4, where the errors are statistical, experimental systematic, systematic due to residual form-factor uncertainties in the signal, and systematic due to residual form-factor uncertainties in the cross-feed modes, respectively. We also find B(B⁺→ηl⁺ν)=(0.84±0.31±0.16±0.09)×10^-4, consistent with what is expected from the B→πlν mode and quark model symmetries. We extract |V_ub| using light-cone sum rules for 0⩽q²<16 GeV² and lattice QCD for 16 GeV²⩽q²<q²_max. Combining both intervals yields |V_ub|=(3.24±0.22±0.13^+0.55_-0.39±0.09)×10^-3 for πlν, and |V_ub|=(3.00±0.21^+0.29+0.49_-0.35-0.38±0.28)×10^-3 for ρlν, where the errors are statistical, experimental systematic, theoretical, and ρlν form-factor shape, respectively. Our combined value from both decay modes is |V_ub|=(3.17±0.17^+0.16+0.53_-0.17-0.39±0.03)×10^-3.