Have Heavy Ion Collisions at CERN Reached the Quark–Gluon Plasma?

With Brookhaven's Relativistic Heavy Ion Collider (RHIC) about to begin its experimental program and CERN's heavy‐ion program winding down at the venerable Super Proton Synchrotron (SPS), a celebratory day of talks at CERN was convoked in February to summarize six years of investigating nuclear matter in extremis at the SPS with a relativistic beam of lead ions. Much of the discussion that day revolved around the question of whether or not the CERN experiments had achieved fleeting visits to the quark–gluon plasma—the promised land envisioned by quantum chromodynamics. QCD is the standard field theory of nuclear matter in terms of its quark constituents and the gluons that bind them.