Molecular Probe for Electroweak Physics

Parity nonconservation (PNC) arises in atoms and molecules due to neutral current electroweak (EW) interactions. Our experiment is sensitive to nuclear spin-dependent (NSD)-PNC including electron-vector times nucleon-axial (VeAn) interaction due to $Z^0$exchange. VeAn terms are suppressed in the Standard Model (SM) making NSD radiative corrections from weak interactions within the nucleus, known as nuclear anapole moments, significant to the overall NSD-PNC signal. We report on our experiment using rotational hyperfine (HF) levels of well understood diatomic molecules to study NSD-PNC. Initially, one state, B, of a pair of opposite parity HF ground states, A and B, of the molecule is depleted. In the interaction region (IR), A and B are Zeeman shifted to near degeneracy in order to amplify perturbative state mixing caused by NSD-PNC interactions. Interference with Stark-induced mixing is revealed using laser-induced fluorescence from B emerging from the IR. This technique is applicable to a wide class of molecules and the variety of nuclei within so that VeAn and anapole contributions to NSD-PNC can be deciphered. This will yield new anapole results and constrain VeAn coupling constants to up and down quarks which are at present poorly characterized SM parameters.