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managed for the U.S. Department of Energy
by Brookhaven Science Associates, a company
founded by Stony Brook University and Battelle
RHIC Data Basics
What energy density has been reached?
About 5 billion electron volts (GeV) per cubic fermi (one fermi is 10-15 meters), or at least 30 times the total energy density in nuclei at rest.
What is the hot zone size?
The size of the hot zone is about the size of a gold nucleus. The system explodes outward to about twice that size, but this size expansion appears smaller than expected.
What temperature has been reached and has QGP been produced?
The temperature in a RHIC collision relates to the notion of thermal equilibrium, wherein the individual quarks and gluons produced in the collision have averaged their energies through numerous mutual interactions. If the RHIC collisions can attain equilibrium at a temperature of 175 million electron volts (MeV), which is approximately three trillion degrees Fahrenheit, or higher, then it will be virtually certain that quark gluon plasma (QGP) has been created. Some RHIC data indicate that this temperature has been reached, but proving it will take another year or two of analysis, plus additional experimental RHIC data.
What is the net baryon density?
The term baryon is used generically for protons, neutrons, and other particles made up of quarks. Anti-baryons are particles such as anti-protons which are made up of three anti-quarks. The early universe had a very low baryon-to-anti-baryon ratio with a proton/anti-proton ratio of 1.000000001. At RHIC, scientists have measured a proton/anti-proton ratio of about 1.3. For the first time in heavy-ion collisions, more baryons are pair-produced than are present from the colliding gold nuclei.