Order αs2β0 correction to the charged lepton spectrum in b→cscr(l)bar νscr(l) decays

We compute the αs2β0 part of the two-loop QCD corrections to the charged lepton spectrum in b→cscr(l)bar νscr(l) decays and find them to be about 50% of the first order corrections at all lepton energies, except those close to the end point. Including these corrections we extract the central values bar Λ=0.33 GeV and λ1=-0.17 GeV2 for the HQET matrix elements and use them to determine the MS b and c quark masses, and |Vcb|. copyright 1997 The American Physical Society