New Observation of Parity Nonconservation in Atomic Thallium

Abstract

Refined observations of parity nonconservation in the $6^{2}P_{\frac{1}{2}}\ensuremath{-}7^{2}P_{\frac{1}{2}}$ transition in $_{81}^{203,\phantom{\rule{0ex}{0ex}}205}\mathrm{Tl}$ are reported. 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 the Stark $E1$ amplitude with $M1$ and parity-nonconserving $E1$ amplitudes. Detection of this polarization yields the circular dichroism $\ensuremath{\delta}=+(2.8\ifmmode\pm\else\textpm\fi{}{1.0}{0.9})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$, which agrees with theoretical estimates based on the Weinberg-Salam model, for ${{sin}^{2}\ensuremath{\theta}}_{W}=0.23$.