  Both color screening and regeneration are hot medium effects on charmonium
production in heavy ion collisions. While they affect in an opposite way the
charmonium yield, their competition in transverse dynamics bring sensitivity to
the ratio of averaged transverse momentum suqare for charmonium, which thus can
reveal more nature of the QCD medium created from the collisions. We make an
excitation analysis based on transport approach to illustrate such a picuture.
