critical point

This is the first in an occassional series about Brookhaven's Relativistic Heavy Ion Collider, or, as it's affectionately called, RHIC. Lil John has a theme song for RHIC's latest experimental run. Sorry, sorry! I couldn't resist. RHIC's actual ditty of the moment goes more like this. (Clean version, of course, RHIC doesn't want any soap in its linac). RHIC, which has a maximum potential energy of 200 billion electron volts (GeV), collided gold ions at energies as low as 7.7 GeV this spring -- the lowest ever achieved in the machine. But why go so low? Even at low energies, the gold-gold…