Lepton Spectrum in Semileptonic Charm Decay

Abstract Virtual and real gluon corrections to the charged lepton spectrum in the decay c→s l + ν e are computed, for arbitrary masses of c and s quarks. A comparison with D semileptonic decay data is done, taking into account the Fermi motion of the charmed quark. Good agreement is found for M c =1.75 GeV, M s =0.5 GeV, and with a Fermi momentum of about 0.5 GeV. With the value of M c thus found, the prediction for the charmed particles lifetime is reduced, with respect to previous estimates, to τ c =5·10 −13 s.