Towards measuring the ratio of scalar to vector transition polarizabilities in 7S → 8S transition in francium.*

Our group is working on measuring the strength of highly forbidden atomic transitions induced by the parity violating (PV) exchange of Z bosons between electrons and quarks in francium (Z=87), the heaviest alkali, at TRIUMF where we capture Fr atoms in a magneto-optical trap (MOT) online to ISAC. The atomic parity violation (APV) signal in Fr is ≈ 18 × larger than in Cs. Working on the atomic 7S-8S transition, the PV observable will be the interference between a parity-conserving amplitude, the “Stark induced” E1 amplitude created by applying a DC electric field, E, to mix S and P states, and the vastly weaker PV-induced amplitude. The 7S → 8S Stark spectroscopy is a precursor to atomic parity violation tests. We intend to explore the Stark amplitude, in particular the ratio of its scalar, α, (ε || E) and vector, β, (ε ⊥ E) components, where ε is the laser polarization. APV tests will require an accurate value for β , and the measurement of α/β will provide an important benchmark for theory providing β. The poster will present our plans for the precision determination of this ratio, including the challenges of producing spin-polarized Fr in a MOT environment and the sub-ms switching of magnetic fields.