Mass effects in muon and semileptonic b→c decays

Quantum chromodynamics (QCD) effects in the semileptonic decay b -> cl (nu) over bar are evaluated to the second order in the coupling constant, O(alpha(2)(s)), and to several orders in the expansion in quark masses, m(c)/m(b). Corrections are calculated for the total decay rate as well as for the first two moments of the lepton energy and the hadron system energy distributions. Translated into QED and applied to the muon decay, they decrease its predicted rate by -0.43 ppm.