This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
In the same way that atoms consist of spinning protons, electrons and neutrons, held together by electrical forces, the proton consists of spinning quarks held together by an analogous but mysterious Quantum Chromo Dynamic (QCD) force. Just as the dynamics of atoms are critically tied to the pairing of spin up and spin down electrons within atomic orbital shells, so are the dynamics of protons tied to relationships between spin up and spin down quarks. These relationships between spinning quarks inside a spinning proton are, however, far from fully understood.
Brookhaven National Laboratory has been the first to build a proton collider accelerator that allows experimenters to prepare the spin orientation of pairs of protons before they collide at high energy, up to 500 GeV in the center of mass. It is found that when the spins are aligned with an axis perpendicular to the motion of the protons, high energy particles (neutral pions, etas and jets of particles) produced in the very forward directions are sensitive to the orientation of this pre-selected spin axis. This research uses a lead-glass calorimeter in the forward region of the larger STAR detector to make measurements that can sort out the dependence of production of these particles upon our choice of initial proton spin directions. The value of these measurements is in the challenge presented to the theory of QCD to explain these interesting spin effects. Current theory is quite specific about how free quarks would interact and how that interaction depends upon spin. What we hope to learn from this research goes to the fundamental and unresolved questions about the unique interactions of these quarks within their environment inside the proton. Ultimately, the goal is to understand the most basic nature of the proton as a composite object. The research involves participation of undergraduate students who assist in fabrication of electronics and in analysis of data from the experiment. One component will also involve a project done by middle school students.
