Enhanced nuclear spin dependent parity violation effects using the 199HgH molecule

Abstract

Electron interactions with the nuclear-spin-dependent (NSD) parity non-conserving (PNC) anapole moment are strongly enhanced within heteronuclear diatomic molecules. A novel, low-energy optical rotation experiment is being proposed with the aim of observing NSD PNC interactions in HgH. Based on the relativistic coupled cluster method we present a complete calculation of the circular polarization parameter $P=2\text{Im}(E{1}_{PNC})/M1\approx 3\times 10^{-6}\kappa$ for the ${}^2{\Sigma }_{1/2}{\to }^2{\Pi }_{1/2}$ optical transition of HgH, where $\kappa$ is a dimensionless constant determined by the nuclear anapole moment. This provides an improvement in sensitivity to NSD PNC by 2 -- 3 orders of magnitude over the leading atomic Xe, Hg, Tl, Pb and Bi optical rotation experiments, and shows that the proposed measurement will be sensitive enough to extract the ${}^{199}$Hg anapole moment and shed light on the underlying theory of hadronic parity violation.