Semileptonic b-->u decays: lepton invariant mass spectrum

We compute O(alpha(2)(s)) QCD corrections to the lepton invariant mass spectrum in the decay b-->ulnu(l), relevant for the determination of the Cabibbo-Kobayashi-Maskawa matrix element /V(ub)/. Our method can also be used to evaluate moments of the lepton energy distribution with an O(alpha(2)(s)) accuracy. The Abelian part of our result gives the neutrino invariant mass spectrum in the muon decay and, upon integration, the O(alpha(2)) correction to the muon lifetime.