Lawrence Berkeley National Laboratory

With the expected large increase in datasets, previously not measured decays will be studied at Belle II. We derive standard model predictions for the B→Xuτν¯ decay rate and distributions. The region in the lepton energy spectrum where higher-dimension operators in the local operator product expansion need to be resummed into the b-quark light-cone distribution function is a significantly greater fraction of the phase space than for massless leptons. The finite τ mass has the novel effect of shifting and squeezing how the distribution function enters the lepton energy spectrum. We also derive new predictions for the τ polarization.