LATTICE STUDY OF THE DECAY (B)OVER-BAR(0)-]P(-)(V)OVER-BAR(L) - MODEL-INDEPENDENT DETERMINATION OF VERTICAL-BAR-V-UB-VERTICAL-BAR()L()

We present results of a lattice computation of the vector and axial-ve ctor current matrix elements relevant for the semileptonic decay (B) o ver bar(0) --> rho(+)l(-)<(nu)over bar>(l). The computations are perfo rmed in the quenched approximation of lattice QCD on a 24(3) x 48 latt ice at beta = 6.2, using an O(a) improved fermionic action. Our princi pal 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 bey ond the charm endpoint, allowing a model-independent extraction of \V- ub\ from experimental measurements. Heavy quark symmetry relations bet ween radiative and semileptonic decays of (B) over bar mesons into lig ht vector mesons are also discussed.