Precise Measurement of Parity Nonconserving Optical Rotation in Atomic Thallium

We report a new measurement of parity nonconserving (PNC) optical rotation on the ${6p}_{1/2}$- ${6p}_{3/2}$ transition in atomic thallium near 1283 nm. The result expressed in terms of the quantity $R=\mathrm{Im}\{{E1\mathrm{}}^{\mathrm{PNC}}/M1\mathrm{}\}$ is $-(15.68\pm 0.45)\times {10}^{-8\mathrm{}}$, and is consistent with current calculations based on the standard model. In addition, limits have been set on the much smaller nuclear spin-dependent rotation amplitude at $R_S=(0.04\pm 0.20)\times 10^{-8\mathrm{}}$; this is consistent with theoretical estimates which include a nuclear anapole contribution.