Physics Colloquium - September 26, 2013

Deconstructing the Partonic Origins of the Proton Spin

Abstract: The discovery of quarks in the 1960's launched a now classic question in nuclear physics: How do the interactions between quarks and gluons produce the fundamental properties of the proton and neutron? The nucleon electric charge is simply the sum of the valence quark charges, while the mass is largely due to the energy stored in the color fields or gluons. In contrast, it is not yet understood how the spin and orbital angular momentum of three valence quarks and a nearly infinite number of gluons and sea quarks combine to produce a spin 1/2 nucleon. Inclusive deep inelastic scattering experiments have limited the sum of the quark contribution to less than a third of the total nucleon helicity distribution. Alternative measurements and techniques, currently being pursued in experiments worldwide, are needed to provide precision insights into the gluon spin, the flavor separated quark spin and the partonic orbital momenta contributions. This talk will present the most recent experimental contributions to these goals from the STAR spin program at the Relativistic Heavy Ion Collider.

Renee Fatemi

Department of Physics and Astronomy
University of Kentucky