Electroweak Physics in Molecules

We report on recent progress of our program to measure nuclear spin-dependent parity nonconservation (NSD-PNC) in electron-nucleon interactions.~ We probe enhanced NSD-PNC signals from the mixing of rotational/hyperfine states in diatomic molecules that are Zeeman shifted to near degeneracy.~ The NSD-PNC effect arises from two main sources: the electron-vector/nucleon-axial $\left( {V_e A_n } \right)$ tree-level neutral current (a $Z^0$-mediated coupling parameterized by electroweak constants $C_{\left\{ {2P,N} \right\}} )$, and a hyperfine term resulting from coupling of the nuclear anapole moment (a magnetic moment induced by intra-nuclear electoweak interactions) to the electron's magnetic dipole moment.~ The $V_e A_n $ term is independ. of the nucleon number $A$ of a given nucleus and is suppressed in the Standard Model, while the anapole term scales as $A^{\raise0.5ex\hbox{$\scriptstyle 2$}\kern-0.1em/\kern-0.15em\lower0.25ex\hbox{$\scriptstyle 3$}}$making it the dominant source of NSD-PNC in nuclei with$A>20$.~ Measurements in molecules containing nuclei over a large range of $A$ should allow us to disentangle the two NSD-PNC contributions, increasing available data on nuclear anapole moments and reducing uncertainties in current measurements of $C_{2P} $ and $C_{2N} $.~ Progress includes demonstration of an increased-flux molecular beam source, and a substantial improvement of molecular detection efficiency using a new scheme.