New evidence from the Relativistic Heavy Ion Collider
reveals different kinds of phase changes at different collision energies
Ever wonder how the hot soup of subatomic particles that
filled the early universe transformed into the ordinary matter of today’s
world? Nuclear physicists exploring this question can’t exactly travel back
13.8 billion years to watch what really happened, but they can recreate matter
at the extreme temperatures and densities that existed just after the Big Bang
by smashing together ordinary atomic nuclei at the Relativistic Heavy Ion
Collider (RHIC). At peak performance, this extraordinarily versatile atom
smasher at the U.S. Department of Energy’s Brookhaven National Laboratory reproduces
the primordial soup thousands of times per second. Using sophisticated
detectors to track what happens as exotic particles emerge from the
trillion-degree collision zone and “freeze out” into more familiar forms of
matter, scientists are turning up interesting details about how the transition
takes place.