Recognizing a clear sign that quark-gluon plasma production ‘turns off’ at low energy

Physicists report new evidence that production of an exotic state of matter in collisions of gold nuclei at the Relativistic Heavy Ion Collider (RHIC)—an atom-smasher at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory—can be “turned off” by lowering the collision energy. The “off” signal shows up as a sign change—from negative to positive—in data that describe “higher order” characteristics of the distribution of protons produced in these collisions.