The Relativistic Heavy Ion Collider (RHIC), under construction at Brookhaven National Laboratory, will be the site of a series of experiments seeking to discover the quark-gluon plasma and elucidate its properties. Several observables should exhibit characteristic behaviors if a quark-gluon plasma is indeed created in the laboratory. Four experiments are now under construction for RHIC to measure certain of these observables over kinematic ranges where effects due to quark-gluon plasma formation should be manifest.

The primary motivation for studying nucleus-nucleus collisions at relativistic and ultrarelativistic energies is to investigate matter at high energy densities ([var-epsilon] [much-gt] 1 GeV/fm[sup 3]). Early speculations of possible exotic states of matter focused on the astrophysical implications of abnormal states of dense nuclear matter. Field theoretical calculations predicted abnormal nuclear states and excitation of the vacuum. This generated an initial interest among particle and nuclear physicists to transform the state of the vacuum by using relativistic nucleus-nucleus collisions. Extremely high temperatures, above the Hagedorn limiting temperature, were expected and a phase transition to a system of deconfined quarks and gluons, the Quark-Gluon Plasma (QGP), was predicted. Such a phase of matter would have implications for both early cosmology and stellar evolution. The understanding of the behavior of high temperature nuclear matter is still in its early stages. However, the dynamics of the initial stages of these collisions, which involve hard parton-parton interactions, can be calculated using perturbative QCD. Various theoretical approaches have resulted in predictions that a high temperature (T [approximately] 500 MeV) gluon gas will be formed in the first instants (within 0.3 fm/c) of the collision. Furthermore, QCD lattice calculations exhibit a phase transition between a QGP and hadronic matter at a temperature near 250 MeV. Such phases of matter may have existed shortly after the Big Bang and may exist in the cores of dense stars. An important question is whether such states of matter can be created and studied in the laboratory. The Relativistic Heavy Ion Collider (RHIC) and a full complement of detector systems are being constructed at Brookhaven National Laboratory to investigate these new and fundamental properties of matter.

This introductory talk contains a brief discussion of future experiments at RHIC related to physics of superdense matter. In particular, we consider the relation between space-time picture of the collision and spectra of the observed secondaries. We discuss where one should look for QGP signals and for possible manifestation of the phase transition. We pay more attention to a rather new topic: hadron modification in the gas phase, which is interesting by itself as a collective phenomenon, and also as a precursor indicating what happens with hadrons near the phase transition. We briefly review current understanding of the photon physics, dilepton production, charm and strangeness and J/[psi] suppression. At the end we try to classify all possible experiments. 47 refs., 3 figs.

Understanding of protons and neutrons, or "nucleons"â€"the building blocks of atomic nucleiâ€"has advanced dramatically, both theoretically and experimentally, in the past half century. A central goal of modern nuclear physics is to understand the structure of the proton and neutron directly from the dynamics of their quarks and gluons governed by the theory of their interactions, quantum chromodynamics (QCD), and how nuclear interactions between protons and neutrons emerge from these dynamics. With deeper understanding of the quark-gluon structure of matter, scientists are poised to reach a deeper picture of these building blocks, and atomic nuclei themselves, as collective many-body systems with new emergent behavior. The development of a U.S. domestic electron-ion collider (EIC) facility has the potential to answer questions that are central to completing an understanding of atoms and integral to the agenda of nuclear physics today. This study assesses the merits and significance of the science that could be addressed by an EIC, and its importance to nuclear physics in particular and to the physical sciences in general. It evaluates the significance of the science that would be enabled by the construction of an EIC, its benefits to U.S. leadership in nuclear physics, and the benefits to other fields of science of a U.S.-based EIC.

The Relativistic Heavy Ion Collider (RHIC) at BNL has produced two physics runs with Au+Au collisions since its startup in 2000 at energies sqrt(s) = 130 and 200 GeV/nucleon-pair. The main motivation for the RHIC program is to search for Quark Matter, which may be produced in these collisions. This talk will focus on RHIC results obtained with the STAR experiment, and where we are with the Quark Matter search.

The collisions of two beams of heavy-ion particles, atoms stripped of their electrons, speeding around BNL's immense Relativistic Heavy Ion Collider (RHIC) have long been expected to create a "quark-gluon plasma" in which the quarks and gluons that make up the protons and neutrons in the ions would move freely in a plasma-like system. But the final particles, detectable in the four experiments placed around the RHIC ring, tend to hide information about the earlier, hotter stage. So it is a challenge to elucidate the nature of the primordial system. What surprised scientists, however, was how strongly the quarks and gluons seemed to interact during the collision. This strong interaction makes the system produced at RHIC behave almost like a perfect fluid, one in which the hot matter formed shows a high degree of collectivity among the particles, rather than a gas, in which individual molecules move about randomly. Evidence from the four RHIC detectors has shown that the system formed at RHIC is potentially the most perfect fluid found in nature, at least since a few microseconds after the Big Bang, a state which RHIC was built to re-create. This result is all the more amazing since the system is so small, the collisions forming over distances 100 times smaller than a proton, and forms so quickly, in times on the order of a millionth of a billionth of a billionth of a second (10-24 seconds). It was even interesting enough to the wider physics community to warrant first place in the American Institute of Physics' year-end review of top physics stories.