This is a three-year project primarily to carry out experiments with relativistic heavy ion collisions. The goals for this program are three-fold. The first goal is to study the space-time properties of the extremely dense matter created in collisions between heavy nuclei at the highest achievable energies. It is believed that Quark Matter is created in these collisions, characterized by a large collection of quarks and gluons, the microscopic components of normal matter such as protons and neutrons. The second goal is to study the bulk phase structure of Quantum Chromodynamics (QCD), believed to be the correct theory to describe interactions between quarks and gluons. This will be achieved by varying the conditions of the collision to lower energies in order to probe the transition(s) between normal matter and Quark Matter. The third goal is to take the tools developed to study bulk physics in heavy ion collisions and apply them to proton-proton collisions at similar energies. We will look particularly for collective behavior, such as hydrodynamic flow, in these collisions. If our initial reports of such flow in proton-proton collisions are confirmed at these higher energies, this raises important issues about the nature of flow, and the nature of the initial state of these collisions.
In the present project, relativistic heavy ion collisions will be studied with gold-gold collisions at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL), and with lead-lead collisions at the Large Hadron Collider (LHC) at CERN in Geneva. RHIC, which started delivering beams in Summer 2000, is the highest energy heavy ion accelerator now in operation. In order to look for signatures that a phase transition to Quark Matter has taken place, one must study the properties of the particles produced in the collisions, such as particle momenta and multiplicities of each type that can be detected (e.g. pions, kaons, protons, and more exotic particles). This will be done at RHIC using the large acceptance detectors of the STAR experiment, which can sample most of the interesting particles per collision. The information obtained in this way can be used to determine, for example, the physical size of the interaction region (using two-particle interferometry), the temperatures reached in the collisions (from particle momentum distributions) and exotic particle production such as strange baryons. In addition, studies of proton-proton and lead-lead collisions at even higher energies at the LHC with the ALICE experiment will begin by April 2010. The LHC will provide beams 30 times higher in center-of-mass energy than RHIC, i.e. cosmic ray energies, making for a useful comparison with results from RHIC.
There are broader impacts to society of this project in the areas of education, technology and computing. Since undergraduate students, graduate students and postdoctoral researchers will play key roles in this project, training will be provided to these groups in how to carry out research in large collaborations and in general problem solving skills. This research requires large-scale computing in order to acquire and analyze data on the teraflop and terabyte scale, and new methods in information science, such as computing grid systems, will be developed which can enhance the computing power of society as a whole.
