Comment on studying the corrections to factorization in

Abstract We propose studying the mechanism of factorization in exclusive decays of the form B→D (∗) X by examining the differential decay rate as a function of the invariant mass of the light hadronic state X . If factorization works primarily due to the large N c limit then its accuracy is not expected to decrease as the X invariant mass increases. However, if factorization is mostly a consequence of perturbative QCD then the corrections should grow with the X invariant mass. Combining data for hadronic tau decays and semileptonic B decays allows tests of factorization to be made for a variety of final states. We discuss the examples of B→D ∗ π + π − π − π 0 and B→D ∗ ωπ − . The mode B→D ∗ ωπ − will allow a precision study of the dependence of the corrections to factorization on the invariant mass of the light hadronic state.