This grant supports research to complete the determination of the weak charge of the proton and investigate new aspects of the Standard Model of fundamental matter and interactions. The Standard Model describes three of the four forces of nature in an elegant manner; those three forces are the electromagnetic interaction, the weak interaction, and the strong interaction. The weak charge of the proton is a basic property, like its electric charge and mass, which determines the proton's response to the weak interaction. It is also related to how the weak and electromagnetic interactions mix with each other. Because the Standard Model predicts how that mixing varies with the amount of momentum that is exchanged in an interaction, a precise measurement of the proton's weak charge at a low value of momentum transfer is a rigorous test of the Standard Model. Additionally, it is sensitive to physics not yet included in the Standard Model. The research program of this award also includes measurements of semi-inclusive deep inelastic scattering that is sensitive to charge symmetry breaking at the quark level and further extends our understanding of fundamental interactions.
The research group supported by this grant will re-commission the Mott polarimeter at Jefferson Lab. That polarimeter will measure the alignment of electron spins in the electron beam of Jefferson Lab; knowing that alignment is crucial to providing polarized electron beams to the four experimental halls of the Lab. Both hardware and software issues will be addressed in this project so the student and postdoctoral researchers will gain a wide range of valuable skills. These broader impacts on the polarized program of Jefferson Lab and the training of young scientists are interwoven into the research program.
