In the course of a high energy collision between two large nuclei, the matter in the region of the impact experiences extremes in pressure and temperature. Normally, a nucleus can be understood as a 'cold liquid drop' of nuclear matter. But during the course of an interaction with another nucleus, one can observe the effects of heating and compression. This allows us to study the 'equation of state' of nuclear matter. As we raise the energy of the projectile, the first interesting effect is that nuclear matter exhibits a 'phase transition' from a cold-liquid state to a hot-gaseous state. In experiments at the Bevalac accelerator at Berkeley our group has been studying the nature of this phase transition.
At the Brookhaven Alternating Gradient Synchrotron the collisions between nucleons become sufficiently violent to shatter nucleons (neutrons and protons) into their constituent quarks and to create quark-antiquark pairs from the vacuum. At these energies, we are studying the effect that the hot dense nuclear matter has on the production of strange and exotic particles and learning about the nature of the hadronic gas.
As one continues to raise the energy of the projectile, the pressures and temperatures become high enough to 'melt' nucleons and to enter yet another 'phase' of nuclear matter, the quark-gluon plasma, a phase of matter that has not existed since the big bang. At experiments at the Super Proton Synchrotron at CERN we are searching for evidence of ignition of such a plasma. This has not been conclusively demonstrated in the experiments which have been completed with oxygen or sulfur beams, but we are hopeful that the new experiments at CERN using lead beams will finally combine sufficient quantities of nuclear matter with sufficient energy density to enter this new state of matter. The lead beams program will be producing its first results in late 1994.
The final experiment in our series takes us back to the Brookhaven Laboratory where they are constructing the Relativistic Heavy Ion Collider which will collide two gold beams, each with 100 GeV/n, this is equivalent to a fixed target experiment at 400 GeV/n. This machine will be ready for operations in early 1999 and with it we expect to produce quark-gluon plasma in sufficient quantities to study its characteristics.
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