Graduate Lunch Talk: Emine Altuntas, Yale Physics, “Nuclear Spin Dependent Parity Violation in Diatomic Molecules”

Parity, one of the three fundamental symmetries of nature along with time reversal and charge conjugation, is not preserved by weak interactions. In atomic systems, parity violation (PV) effects are described in terms of two categories: (1) Spin independent PV effects that arise from the weak charge of the nucleus, QW; and (2) Spin dependent contributions due to interactions inside the nucleus. The former is well studied, as it is a relatively large effect with well-characterized theoretical predictions. On the other hand, nuclear spin dependent parity violation (NSD-PV) effects are small (~1% of the spin independent PV effects) and require more precise measurements. To date the only nonzero measurement of parity violation in atoms was made in cesium but the uncertainty in this measurement is very large and there is disagreement with other data. We study NSD-PV effects using diatomic molecules, which have rotational hyperfine levels with energy splittings that are about four orders of magnitude smaller than the typical 1 eV atomic energy scale. We amplify observable signals from NSD-PV by about seven additional orders of magnitude by bringing two rotational levels of opposite parity close to degeneracy with a strong magnetic field. The NSD-PV interaction matrix element is measured using a Stark-interference technique. I will present our latest results that demonstrate statistical sensitivity to NSD-PV effects surpassing that of any previous atomic parity violation measurement. To test for systematic errors we are using 138BaF, which has no unpaired nucleons and so spin-dependent parity violation effects are zero. I will discuss our methods for measuring and nullifying the systematic effects due to combination of non-reversing stray E-fields (Enr) with B-field inhomogeneities.