Study of B→πlν and B→ρlν decays and determination of vertical bar Vub vertical bar

We present an analysis of exclusive charmless semileptonic B-meson decays based on 83x106 BB pairs recorded with the BABAR detector at the Υ(4S) resonance. Using isospin symmetry, we measure branching fractions B(B0→π-l+ν)=(1.38±0.10±0.16±0.08)x10-4 and B(B0→ρ-l+ν)=(2.14±0.21±0.48±0.28)x10-4, where the errors are statistical, experimental systematic, and due to form-factor shape uncertainties. We compare the measured distribution in q2, the momentum-transfer squared, with theoretical predictions for the form factors from lattice QCD and light-cone sum rules, and extract the Cabibbo-Kobayashi-Maskawa (CKM) matrix element |Vub|=(3.82±0.14±0.22±0.11-0.52+0.88)x10-3 from B→πlν, where the fourth error reflects the uncertainty of the form-factor normalization