Colloquium: Prof. Renee Fatemi, University of Kentucky
Title: "Deconstructing the Partonic Origins of the Proton Spin"
Abstract: The discovery of quarks in the 1960's launched a now classic question in particle 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 valence + sea 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 contribution and partonic orbital angular momenta. This talk will provide a historical review of spin structure experiments before discussing the most recent experimental constraints on the gluon helicity distribution from the spin program at the Relativistic Heavy Ion Collider.