Protons, each made of three quarks, form as the QGP cools, and can serve as stand-ins for the overall baryon density (baryons being all particles made of three quarks, which also includes neutrons). To look for signs of a critical point-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)-the scientists look for fluctuations in things they measure coming out of the collisions.Ī previous study found tantalizing signs of the type of fluctuations scientists would expect around the critical point by looking at the number of net protons produced at the various collision energies. STAR physicists are exploring collisions at different energies, turning the "knobs" of temperature and baryon density, to look for signs of a "critical point." RHIC's collisions "melt" protons and neutrons to create quark-gluon plasma (QGP). Mapping nuclear phase changes is like studying how water changes under different conditions of temperature and pressure (net baryon density for nuclear matter). 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. 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. 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. “It’s important scientifically and to human understanding of where we come from.” Critical point search party “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. Proof of a critical point-a point where there’s a change in the way nuclear matter transforms from one phase to another-is key to answering fundamental questions about the makeup of our universe. New findings from members of RHIC’s STAR Collaboration published in Physical Review Letters hint that calculations predicting how many lightweight nuclei should emerge from collisions could help mark that spot on the roadmap of nuclear phase changes. Department of Energy (DOE) Office of Science user facility for nuclear physics research at DOE’s Brookhaven National Laboratory, are searching for evidence that nails down a so-called critical point in the way nuclear matter changes from one phase to another. UPTON, NY-Physicists analyzing data from gold ion smashups at the Relativistic Heavy Ion Collider (RHIC), a U.S. The "heart" of the STAR detector at Brookhaven's Relativistic Heavy Ion Collider is the Time Projection Chamber, which tracks and identifies particles emerging from ion collisions.
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