Candidate answer to the black-hole-production sub-question under the assumption that gravity is standard; the rival branch (TeV-scale gravity with large extra dimensions, under which production becomes possible) postdates this analysis’s frame — the paper’s estimate quantifies exactly how far standard gravity is from criticality, which is why the entire later black-hole debate runs through extra-dimension models. The paper adds that RHIC is actually less effective at raising nuclear density than lower-energy machines (less stopping power), and that no phenomenon suggestive of gravitational clumping has ever been observed in any collision.