  The transverse momentum (pt) dependence of J/psi production in heavy ion
collisions is investigated in a transport model with both initial production
and continuous regeneration of charmonia. The competition between the two
production mechanisms results in a pt suppression in central collisions, the
gluon multi-scattering in the initial stage leads to a high pt enhancement, and
the regeneration populates J/psis at low pt region and induces a minimum in
R_AA(pt). These three phenomena are indeed observed in both 200 GeV Cu+Cu and
Au+Au collisions at RHIC energy.
