Open charm as a probe of preequilibrium dynamics in nuclear collisions

The preequilibrium contribution to open charm production in nuclear collisions at \ensuremath{\surd}s =200 A GeV is calculated and shown to be sensitive to the early time evolution of the initial minijet gluon plasma. The role of charm as a probe of the formation zone physics and correlations between momentum and space-time coordinates is emphasized. While ideal (Bjorken) correlation between the rapidity y and space-time rapidity \ensuremath{\eta} of minijet gluons suppresses greatly the preequilibrium yield, the minimal correlation with finite geometrical spread enhances the initial fusion rate by a factor \ensuremath{\sim}2 in the moderate ${\mathit{p}}_{\mathrm{\ensuremath{\perp}}}$\ensuremath{\sim}2--6 GeV range. That is dominated by fusion of ``semihard'' ${\mathit{p}}_{\mathrm{\ensuremath{\perp}}}$>2 GeV minijet gluons and secondary ``soft'' ${\mathit{p}}_{\mathrm{\ensuremath{\perp}}}$2 GeV gluons from initial and final state radiation. The ``intrinsic'' charm process is negligible in the midrapidity domain.

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