The focus of the the OSU Relativistic Heavy Ion Group is the study of nuclear matter under the most extreme conditions of pressure, density, and temperature. While the nuclear matter found at the center of atoms is extremely dense (about two hundred billion times as dense as water), matter at the core of neutron stars is compressed up to 10 times more. Similarly, our own universe evolved from a state in which matter densities far exceeded those found at the center of an atomic nucleus. Studying the physics of how nuclear matter behaves under extreme conditions will further our understanding of our universe in fundamental areas beyond traditional nuclear physics.
At low excitation energy and near normal density, the properties of nuclear matter are fairly well understood. As nuclear systems become compressed or heated, a rich set of phenomena is observed, including multi-step particle production, in-medium modification of the particle properties, and at least one phase transition, from a liquid to a gaseous phase. At even higher energies and densities, a second phase transition is expected to occur, to the type of matter believed to have existed about one microsecond after the Big Bang. This transition, predicted by most models, involves the liberation of the quarks and gluons that make up the protons and neutrons inside the nucleus. The new state of matter, called the Quark Gluon Plasma, exists for only an instant, but study of its properties should challenge our understanding of the strong force in a regime where calculations are the most difficult.
To compress and heat nuclear matter, we study collisions of heavy nuclei (typically gold or lead) at the highest possible energies. This research involves collaborative experiments with very large particle detectors at national labs in the U.S. (BNL AGS: E895, E896, RHIC: STAR) and Europe (CERN SPS: NA44, LHC: ALICE). The OSU group is involved with detector (e.g. silicon drift) and software development and data analysis aimed at identifying and studying this second as-yet-unobserved phase transition in nuclear matter.