Low Energy Tests of the Standard Model

Low-energy precision measurement of fundamental parameters in the electroweak theory provide information on new physics at high mass scales, beyond the reach of present-day colliders. Historically, low energy tests of the electroweak theory were critical in establishing the validity of the Standard Model; however, today the motivation for performing precision low-energy measurements is to search for beyond Standard Model physics. We review briefly the study of low energy measurements of the electroweak mixing angle, with a focus on a new measurement coming from the observation of a parity-violating asymmetry in the scattering of high energy polarized electrons by unpolarized electrons in a liquid hydrogen target. The experiment was performed at the Stanford Linear Accelerator Center. The present experiment is sensitive to new physics at the TeV energy scale. We also compare the results to other low-energy tests of the electroweak theory, and briefly discuss future planned low-energy measurements.