Parity Nonconservation in Atomic Thallium

We present new measurements of parity conservation in the 293-nm transition in atomic ${}_{81}{}^{205}{}_{}{}^{}\mathrm{Tl}$. Linearly polarized 293-nm photons, polarization $\hat{\epsilon }$, are absorbed by $6{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ atoms in crossed electric and magnetic fields. The transition probability for each Zeeman component contains a term proportional to $\hat{\epsilon }·\overrightarrow{\mathrm{B}}\hat{\epsilon }·\overrightarrow{\mathrm{E}}\times \overrightarrow{\mathrm{B}}$ arising from interference between the Stark $E1$ amplitude $\beta E$ and the parity-nonconserving $E1$ amplitude ${\mathcal{E}}_p$. Our result, ${\left[\mathrm{Im}\frac{{\mathcal{E}}_p}{\beta }\right]}_{\mathrm{expt}}=-1.73\mathrm{}\pm 0.33$ mV/cm, is compared with estimates based on the standard electroweak model.