Professor & Chair
Ph.D. 1996, Yale University
Why are the constituents of the proton confined? Where does its mass come from? What makes up its spin? These fundamental Physics questions have fascinated me for years and drove me to utilize the Relativistic Heavy Ion Collider (RHIC). This novel collider is the major facility for high-energy nuclear physics. My spin physics, program utilizes collisions of polarized protons, while my heavy-ion physics, program utilizes collisions of heavy nuclei. The spin and heavy ion physics communities have developed separately as they utilize completely different experimental and theoretical techniques. The physics underlying both fields, however, have intriguing similarities. RHIC therefore provides a unique opportunity to pursue spin and heavy-ion physics as well as to explore the connections between two seemingly disparate physics investigations.
Spin is a property of particles as fundamental as charge and mass. The spin of the proton was first determined in 1927, yet we still do not know what makes up the spin of the proton. It was believed that the spin was carried by the quarks that make up the proton. However, experiments in the 1980’s led to the startling discovery that quarks contribute very little to the proton spin, setting off the "proton spin crisis”. It is now theorized that the spin is carried by gluons, which hold the proton together. The spin physics program at RHIC offers the first chance to test this hypothesis experimentally. Spin measurements have historically yielded surprising results and are a stringent test to theories as spin is an intrinsically relativistic and quantum mechanical aspect of particle interactions.
We collide heavy ions at high energy to produce nuclear matter at extreme conditions of temperature and density. In this environment, we expect nuclear matter to be in a new state where quarks are free to move about and particles have very little mass, allowing us to investigate such fundamental questions as where most of the mass that surrounds us comes from. The National Research Council's Committee of Physics of the Universe developed a list of the 11 Greatest Unanswered Questions of Physics. One of the questions they pose is whether there are "new states of matter at ultrahigh temperatures and densities. This is the subject of heavy-ion physics.
My current main activity is in the PHENIX experiment at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. PHENIX is an ambitious experiment capable of identifying photons, electrons, and muons. Its capability to measure low mass di-electrons allows us to search for the partial restoration of chiral symmetry through the decay of the phi particle, which is believed to be the most power experimental tool for this search. The detectors ability to measure photons and leptons in polarized proton-proton collisions allow the potential to make significant measurements which are sensitive to the gluon structure function.
Within PHENIX I was co-convenor of the spin physics working group, am co-led the central arm first level trigger and was the physicist in charge of electronics of the Time Expansion Chamber. I am the PHENIX Institutional Board member for UC Riverside, and leading the production electronics for the RPC upgrade to the muon trigger that will enable the measurement of anti-quark helicity distributions.
I was actively involved in a search for strange quark matter with Brookhaven AGS experiment E864 since its inception. My Ph.D. thesis was on a "Search for positively charged strange quark matter".