Lattice study of the decay (B)over-bar(0)->p(+)l(-)(v)over-bar(l): Model-independent determination of vertical bar V-ub vertical bar

We present results of a lattice computation of the vector and axial-vector current matrix elements relevant for the semileptonic decay (B) over bar(0) --> rho(+)l(-)<(nu)over bar>(l). The computations are performed in the quenched approximation of lattice QCD on a 24(3) x 48 lattice at beta = 6.2, using an O(a) improved fermionic action. Our principal result is for the differential decay rate, d Gamma/dq(2), for the decay (B) over bar(0) --> rho(+)l(-)<(nu)over bar>(l), in a region beyond the charm endpoint, allowing a model-independent extraction of \V-ub\ from experimental measurements. Heavy quark symmetry relations between radiative and semileptonic decays of (B) over bar mesons into light vector mesons are also discussed.