  Double logarithms of $Q^2/m_c^2$ that appear in the cross section for
$e^+e^-\to J/\psi + \eta_c$ at next-to-leading order (NLO) in the strong
coupling $\alpha_s$ account for the bulk of the NLO correction at $B$-factory
energies. (Here, $Q^2$ is the square of the center-of-momentum energy, and
$m_c$ is the charm-quark mass.) We analyze the double logarithms that appear in
the contribution of each NLO Feynman diagram, and we find that the double
logarithms arise from both the Sudakov and the end-point regions of the loop
integration. The Sudakov double logarithms cancel in the sum over all diagrams.
We show that the end-point region of integration can be interpreted as a
pinch-singular region in which a spectator fermion line becomes soft or soft
and collinear to a produced meson. This interpretation may be important in
establishing factorization theorems for helicity-flip processes, such as
$e^+e^-\to J/\psi + \eta_c$, and in resumming logarithms of $Q^2/m_c^2$ to all
orders in $\alpha_s$.
