Differential distributions for heavy quark production depend on the heavy
quark mass and other momentum scales, which can yield additional large
logarithms and inhibit accurate predictions. Logarithms involving the heavy
quark mass can be summed in heavy quark parton distribution functions in the
ACOT factorization scheme. A second class of logarithms involving the
heavy-quark transverse momentum can be summed using an extension of
Collins-Soper-Sterman (CSS) formalism. We perform a systematic summation of
logarithms of both types, thereby obtaining an accurate description of
heavy-quark differential distributions at all energies. Our method essentially
combines the ACOT and CSS approaches. As an example, we present angular
distributions for bottom quarks produced in parity-conserving events at large
momentum transfers Q at the ep collider HERA.Comment: 22 pages, 6 figures; minor change
