Parity violation in electron-electron

Scattering has now been seen. According to parity conservation, physics is the same in both ordinary and mirror worlds. Of the four known physical forces, only the weak nuclear force does not conserve parity. Since the 1950s, parity violation has been observed in several reactions, but never before in relatively low-energy electron-electron scattering: Electrons participate not only in electromagnetic interactions, but also in weak nuclear interactions via beta decay and related processes. The E158 Collaboration at SLAC scattered 50-GeV beams of longitudinally polarized electrons off electrons in a liquid hydrogen target and measured the fractional difference in scattering rates for the two polarizations. The observed asymmetry not only demonstrated parity violation, but also provided the first direct measurement of the electron’s “weak charge.” The value was in excellent agreement with predictions of the standard model of particle physics. (P. L. Anthony et al. , Phys. Rev. Lett. 92,...