Physicists are studying data from gold ion collisions at the Relativistic Heavy Ion Collider (RHIC) to find evidence of a critical point in the way nuclear matter changes from one phase to another. The RHIC is a U.S. Department of Energy (DOE) Office of Science user facility for nuclear physics research at DOE’s Brookhaven National Laboratory. The new findings from members of RHIC’s STAR Collaboration, published in Physical Review Letters, suggest that calculations predicting how many lightweight nuclei should emerge from collisions could help identify the critical point on the roadmap of nuclear phase changes. The discovery of a critical point is crucial to answering fundamental questions about the composition of our universe.
“You can imagine the nuclear phase diagram as a bridge connecting the past—the Big Bang and the early universe—to visible matter as we know it today, and even neutron stars,” said Xiaofeng Luo, a member of RHIC’s STAR Collaboration from Central China Normal University (CCNU), who led a group of students in this analysis. “It’s important scientifically and to human understanding of where we come from.”
RHIC’s collisions recreate a hot, dense state of matter that existed for a tiny fraction of a second right after the Big Bang some 14 billion years ago. This matter, called a quark-gluon plasma (QGP), is a soup of “free” quarks and gluons—the building blocks of the protons and neutrons that make up atomic nuclei. Colliding heavy ions at various energies allows RHIC physicists to study how the collisions create this primordial soup and how it transitions back into ordinary nuclear matter.
To look for signs of a critical point, the scientists look for fluctuations in things they measure coming out of the collisions. A critical point is where the type of transition from QGP to ordinary matter changes from a smooth crossover (where two phases coexist, as when butter gradually melts on a warm day) to a sudden shift (like water suddenly boiling).
2023-06-02 11:00:03
Post from phys.org