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

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 BB̄ meson pairs collected at the Y(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-_0.54 ^+0.47±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<16GeV ² and lattice QCD for 16 GeV²≤q²<q _max². Combining both intervals yields |V _ub|=(3.24 ±0.22±0.13-_0.39 ^+0.55-0.09)×10^-3 for πℓν, and |V _ub|=(3.00±0.21_0.35^+0.29 _-0.38^+0.494±0.28)×10^-3 for pfv, 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_-0.17+ ^0.16_-0.39^+0.53±0.03)×10 ^-3.