Preliminary Observation of Parity Nonconservation in Atomic Thallium

Abstract

Parity nonconservation is observed in the $6^{2}P_{\frac{1}{2}}\ensuremath{-}7^{2}P_{\frac{1}{2}}$ transition in thallium. Absorption of circularly polarized 293-nm photons by $6^{2}P_{\frac{1}{2}}$ atoms in an $E$ field results in polarization of the $7^{2}P_{\frac{1}{2}}$ state through interference of Stark $E1$ amplitudes with $M1$ and parity-nonconserving $E1$ amplitudes $\mathfrak{M}$ and ${\mathcal{E}}_{p}$. Detection of this polarization yields the circular dichroism $\ensuremath{\delta}=+(5.2\ifmmode\pm\else\textpm\fi{}2.4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$, which agrees in sign and magnitude with theoretical estimates based on the Weinberg-Salam model.