  We study the centrality dependence to be expected if only charmonium
production in the corona survives in high energy nuclear collisions, with full
suppression in the hot, deconfined core. To eliminate cold nuclear matter
effects as far as possible, we consider the ratio of charmonium to open charm
production. The centrality dependence of this ratio is found to follow a
universal geometric form, applicable to both RHIC and LHC in collisions at
central and forward rapidities.
