Two-stage equilibration in high energy heavy ion collisions

Using the (lowest-order) perturbative QCD, we argue that high energy heavy-ion collisions proceed via two stages: equilibration of gluons takes time ${\mathrm{\tau }}_{\mathit{g}}$∼1/2 fm/c, while production and equilibration of quarks needs time at least ${\mathrm{\tau }}_{\mathit{q}}$∼2 fm/c. If so, the initial gluon plasma is much hotter than usually estimated, ${\mathit{T}}_{\mathit{g}}$∼400 MeV, which leads to enhanced charm production and significant modifications of other proposed signals.