From the very beginning, there were hints that particle collisions at the Relativistic Heavy Ion Collider (RHIC) were producing something strange. This U.
S. Department of Energy (DOE) Office of Science User Facility at Brookhaven National Laboratory was designed to recreate the incredibly hot and dense conditions of matter in the early universe by colliding atomic nuclei at high enough energies to "melt" their constituent protons and neutrons. The collisions would "free" those particles' inner building blocks—quarks and gluons—so nuclear physicists could study their behavior unbound from ordinary matter.
Source: phys.org