This award supports research to measure the weak charge of the proton and then use that measurement to 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, that 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 makes well defined predictions of how that mixing varies with the amount of momentum that is exchanged in an interaction, with only one set of very precise measurements existing at very high values of momentum transfer, 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 Qweak experiment at JLab will carry out this precise measurement by scattering polarized electrons from protons and measuring the rate at which they scatter. Extracting the weak charge of the proton from this scattering will require delicate calibrations with specialized equipment. The research group supported by this award will commission the detector that will trigger all other detectors of the calibration phase, and develop the electronics that will be used during the calibration phase. Both hardware and software issues will be addressed in this project so the students and postdoctoral researchers will gain a wide range of valuable skills. Programs to broaden participation of under-represented groups in physics are also supported by this award.
The Standard Model of Forces and Interactions 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 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 makes well defined predictions of how that mixing varies with the amount of momentum that is exchanged in an interaction, a measurement of the proton's weak charge can explore new physics beyond the Standard Model. A collaboration of scientists made a precise measurement of the proton's weak charge by scattering polarized electrons from protons and measuring the rate at which they scatter. Extracting the weak charge of the proton from this scattering required delicate calibrations with specialized equipment. This award supported two graduate students who learned how to design, build, and calibrate particle detectors, analyze data, and simulate complex interactions to understand the data. With only 4% of the acquired data analyzed, the collaboration was able to determine that the weak charge of the proton = 0.064 +/- 0.012; the data also allowed the scientists to determine that the weak charge of the neutron is -0.975 +/- 0.010. The research group supported by this grant will commission the detector that will trigger all other detectors of the calibration phase, and develop the electronics that will be used during the calibration phase.
