Endpoint logarithms in e⁺e^-→ J/π +η_c

We investigate the origin of the double logarithms of Q²/m _c² that appear in the calculation of the cross section for e⁺e^- → J/π +η_c at next-to-leading order in the strong coupling α_s. Here, Q² is the square of the center-of-momentum energy, and mc is the charm-quark mass. We find that, diagram-by-diagram, the double logarithms are accounted for by Sudakov double logarithms and endpoint double logarithms. The Sudakov double logarithms cancel in the sum over all diagrams, but the endpoint double logarithms do not. We reinterpret the endpoint double logarithms in terms of a leading region of loop integration in which a spectator fermion line becomes soft and collinear. This reinterpretation may simplify the process of establishing an all-orders factorization theorem for this helicity-flip process, which, in turn, might allow one to resum logarithms of Q²/m_c² to all orders in α_s. Copyright owned by the author(s).