PHYSICS DEPARTMENT

The research of the High Energy Nuclear Physics Group focuses on the exploration of the equation of state of nuclear matter. The Purdue High Energy Nuclear Physics Group is in the forefront of this exciting area of research.

The goal is the creation and observation of highly excited and unusual states of nuclear matter. Traditional nuclear physics has been devoted to the study of nuclei which are gently perturbed. Using high energy beams of particles, we can create states of nuclear matter that are far removed from the ground state.

Understanding nuclear matter under these extreme conditions will provide fundamental information about the statistical mechanics of those particles (hadrons) that interact via the strong (nuclear) interaction. This experiment is at data taking stage at the Relativistic Heavy Ion Collider (RHIC) at the Brookhaven National Laboratory (BNL). We are presently analyzing data from the experiment. For example, at sufficiently high densities and temperatures, neutrons and protons should "melt" into their constituent quarks, forming the so-called quark-gluon plasma. The resulting nuclear matter should be similar to that which may have existed some microseconds after the Big Bang. We are members of the STAR Collaboration that will seek evidence of quark-gluon plasma formation in collisions between ultrarelativistic gold nuclei. This experiment, to be performed at the Relativistic Heavy Ion Collider (RHIC) at the Brookhaven National Laboratory (BNL), is in its preparation stage and will begin taking data within the next two years.

Our group is also involved in an experiment at BNL designed to search for a new form of nuclear matter that may be in its ultimate state, i.e. at a lower energy than the ground state of traditional nuclei. In this experiment, collisions between two large nuclei might occasionally produce equal measures of up, down, and strange quarks that bind together to form ``strangelets''. Ordinary nuclear matter contains only up and down quarks. The presence of strange quarks may allow the formation of massive, nearly uncharged strangelets. The discovery of strangelets would have repercussions not only for nuclear physics but for cosmology as well. We are presently analyzing data from this experiment.

Particularly challenging is the development of unambiguous signals for phase transitions in very small systems where the number of constituents is in the hundreds to a few thousand. The Purdue Group is studying the liquid-gas phase transition in finite nuclei and has identified unambiguous signals of a critical point which is analogous to the signatures in extended matter. The understanding of this phase transition will provide guidance in the search for the quark-gluon plasma where the number of constituents may be about a thousand.

For inquiries regarding the High Energy Nuclear Physics Group send mail to Dr. Andy Hirsch at hirsch@physics.purdue.edu