Contributions from the Breit interaction in atomic structure calculations account for $1.3\sigma$ of the previously reported $2.5\sigma$ deviation from the standard model in the ${}^{133}\mathrm{Cs}$ weak charge [S. C. Bennett and C. E. Wieman, Phys. Rev. Lett. 82, 2484 (1999)]. The updated corrections for the neutron distribution reduce the discrepancy further to $1.0\sigma$. The updated value of the weak charge is $Q_W{(}^{133}\mathrm{Cs})=-72.65\mathrm{}(28{)}_{\mathrm{expt}}(34{)}_{\mathrm{theor}}$.

• Received 29 November 1999

DOI:https://doi.org/10.1103/PhysRevLett.85.1618