To get a better understanding of the subatomic soup that filled the early universe, and how it "froze out" to form the atoms of today's world, scientists are taking a closer look at the nuclear phase diagram. Like a map that describes how the physical state of water morphs from solid ice to liquid to steam with changes in temperature and pressure, the nuclear phase diagram maps out different phases of the components of atomic nuclei -- from the free quarks and gluons that existed at the dawn of time to the clusters of protons and neutrons that make up the cores of atoms today.
But "melting" atoms and their subatomic building blocks is far more difficult than taking an ice cube out of the freezer on a warm day. It requires huge particle accelerators like the Relativistic Heavy Ion Collider, a nuclear physics scientific user facility at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory, to smash atomic nuclei together at close to the speed of light, and sophisticated detectors and powerful supercomputers to help physicists make sense of what comes out. By studying the collision debris and comparing those experimental observations with predictions from complex calculations, physicists at Brookhaven are plotting specific points on the nuclear phase diagram to reveal details of this extraordinary transition and other characteristics of matter created at RHIC.
To plot the key points where the transition takes place, the scientists are looking for large fluctuations in the excess of certain kinds of particles produced from collision to collision (for example, more protons than antiprotons, or more positively vs. negatively charged particles).
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