  A new mechanism for heavy quarkonium production in high-energy collisions
called the "s-channel cut" was proposed in 2005 by Lansberg, Cudell, and
Kalinovsky. We identify this mechanism physically as the production of a heavy
quark and anti-quark that are on-shell followed by their rescattering to
produce heavy quarkonium. We point out that in the NRQCD factorization
formalism this rescattering mechanism is a contribution to the color-singlet
model term at next-to-next-to-leading order in perturbation theory. Its leading
contribution to the production rate can be calculated without introducing any
additional phenomenological parameters. We calculate the charm-pair
rescattering (or s-channel cut) contribution to the production of J/psi at the
Tevatron and compare it to estimates by Lansberg et al. using phenomenological
models. This contribution competes with the leading-order term in the
color-singlet model at large transverse momentum but is significantly smaller
than the next-to-leading-order term. We conclude that charm-pair rescattering
is not a dominant mechanism for charmonium production in high-energy
collisions.
