Grant: Subatomic Physics Envelope - Research Tools and Instruments

In nature, four fundamental forces exist: gravity, electromagnetism, and the strong and weak nuclear forces. The weak force is the only force which does not look the same when viewed in a mirror. The violation of mirror symmetry is called "parity violation". Precise measurements of parity violation at low energies yield information on the weak force. A deviation from the standard model (the theory of electromagnetic, strong, and weak forces) would signify new physics. Agreement with the standard model would place stringent limits on new theories. It is the goal of this research to perform low-energy measurements of parity violation in order to possibly make new discoveries of physics beyond the standard model.      The Qweak experiment (to be performed at Thomas Jefferson National Accelerator Facility "JLab" in Newport News, VA) will use the technique of scattering electrons from protons to study the weak force.  The results can be compared with measurements of the weak force performed at high energies.  The strength of the weak interaction is expected to vary with energy in a way that is theoretically predictable.  A deviation from the theoretical energy dependence would signify physics beyond the standard model.  The Qweak experiment would represent the most precise measurement of the strength of the weak interaction at low energy.      This proposal is for a quartz scanner detector for Qweak. In Qweak, the scattered electrons will be detected by large fused silica (synthetic quartz) detectors to be built by JLab. It is crucial to understand the paths of electrons through the magnetic spectrometer, and the response of the detectors to electrons. High precision chambers address these issues at low beam currents.  However, a smaller quartz scanner detector, to be scanned across the face of the main detectors, could address these issues at all beam currents, and would allow to extrapolate results at low current to the high currents necessary for production running.  The scanner would also be used to study backgrounds. Devices similar to this one have been used to great success in previous parity-violating electron scattering experiments for these purposes.