This grant supports efforts to measure to a very high precision a fundamental property of the proton and the electron. By comparing our measurements with predicted values we can test the Standard Model of particle physics, our current best theory of fundamental particles and their interactions. Deviations from the predictions will point to new physical processes that are not included in the Standard Model. The Thomas Jefferson National Accelerator Facility, or Jefferson Lab, is the world's leading laboratory for parity-violating electron scattering experiments. In two large collaborative experiments at Jefferson Lab, we will measure the 'weak' charge of the proton and the electron by scattering energetic electrons off a liquid hydrogen target. The weak charge is a property analogous to the well-known electric charge, but mediated by the weak force that is responsible for some radioactive decays. The Qweak experiment started in May 2010 and will collect data until May 2012. This experiment will measure for the first time the weak charge of the proton. Our group will use the new Compton polarimeter to measure the electron beam polarization, and we will develop the track reconstruction software for the determination of the reaction kinematics. The MOLLER experiment is expected to run after 2014, and will measure the weak charge of the electron. Our group is taking a leading role in the development of a novel type of electron beam polarimeter based on electron-electron scattering in polarized atomic hydrogen gas. This will allow for the measurement of the electron beam polarization to the required precision. This new polarimeter will demonstrate technology that can be applied at other accelerators.
In the quest to understand the fundamental structure of matter, most physicists have taken a reductionist approach by breaking matter down to its elementary constituents: electrons, quarks, gluons, etc. In addition to the known elementary particles that constitute the Standard Model of particle physics, there may exist as-of-yet-undiscovered heavier elementary particles. At the energy frontier, ever more powerful accelerators (such as the Large Hadron Collider) aim to create those heavy particles directly. In contrast, at the intensity frontier we make very precise measurements at moderate energy scales. Jefferson Lab is at the forefront of precision measurements using the technique of parity-violating electron scattering, which exploits the small differences between reactions and their mirror image. The development of accelerators, particle detectors, and data analysis techniques has found many applications in industry, from radiation treatment for cancer and medical imaging to financial analysis. At the College of William & Mary, a PhD-granting liberal arts university within 30 minutes of Jefferson Lab, we present our graduate students with excellent career prospects, and we actively involve undergraduate students in the frontiers of research and train them to become the next generation of innovators.
