(The NFL likes parity)

Largest Parity Violation and Other Adventures in Table-Top Physics: Atomic Experiments Push Boundary of Known Physical World

Budker uses atoms of the rare Earth element ytterbium to observe the largest extent of parity violation ever seen in atoms, larger by a factor of 100 compared to previous tests. His goal is to improve the precision of this measurement so that researchers could begin to use the parity-violating process to help measure the distribution of neutrons in nuclei.

Previous experiments from a dozen years ago used Cesium. The parity nonconservation was probed by looking at transitions between S orbital states (6S and 7S for Cesium). The electromagnetic transition between these states is highly forbidden (both having the same angular momentum and even parity) But because the orbitals are spherical they include the nucleus, and the weak interaction mixes in a tiny bit of a P-state transition (odd parity), which is allowed. It’s a tough experiment because you are looking for the small difference between the transitions when you reverse everything, and you start out with a small transition probability. I recall this because we tried trapping Francium when I was at TRIUMF, with the goal of providing an atom with a potentially larger parity-nonconserving subject. The effect varies with Z, and Francium was expected to give an effect that was ~18 times larger than Cesium. We weren’t successful (then) at trapping any, though we did succeed at piquing the interest of a nuclear watchdog organization.