June 5, 2023 ~
Physicists can create an exotic state of matter known as a quark-gluon plasma (QGP) by colliding gold nuclei together. By systematically varying the amount of energy involved in the collision, scientists have shown that the QGP exists in collisions at energies from 200 billion electron volts (GeV) down at least to 19.6 GeV. However, its production appears to be “turned off” at the lowest collision energy, 3 GeV. The “off” signal shows up as a sign change—from negative to positive—in data that describe the distribution of protons produced in these collisions.