  We study the momentum dependence of the production of light nuclei in high
energy collisions in the nucleon coalescence/recombination mechanism. We derive
formulas of the momentum distributions of deuterons ($d$) and helions ($^3$He).
We obtain the analytic expressions of the coalescence factor $B_A$'s ($B_2$ for
$d$ and $B_3$ for $^3$He) as functions of the collision system size and the
momentum. We apply the deduced results to p-p, p-Pb and Pb-Pb collisions to
naturally explain the interesting behaviors of $B_A$ observed in experiments at
the CERN Large Hadron Collider.
