Ytterbium measurements important for parity violation

Researchers at the University of California, Berkley recently reported measurements of a “large parity-violating effect in ytterbium.” Graduate student Dimitri Dounas-Frazer explained that, though the group is encouraged by their results, their work in decreasing percent error continues.

He began his talk by explaining the importance of atomic parity violation and by defining it generally. In a broad sense, research on the topic is motivated by the diverse applications of atomic parity violation, Dounas-Frazer said. It allows table-top testing of the standard model, testing which is complementary to work at CERN. It also serves nuclear physics in that it allows further probing of nuclei.

The effect arises mostly from the symmetry of the universe. The two main forms of symmetry are rotational symmetry, which is connected to the conservation of angular momentum, and inversion symmetry, which is connected to the concept of conservation of parity.

The universe is symmetric under rotation, meaning that if two scientists rotated relative to each other conduct identical experiments, the results should be the same. However, the universe is not symmetric under inversion, meaning that the mirror image experiment might not have the same results. This lack of inversion symmetry gives rise to parity violations, which can be physically interpreted. Analysis of parity violations is made more complicated by the presence of electromagnetic fields on Earth, but is still possible.

Dounas-Frazer also discussed briefly the history of the field and the more technical side of the analysis. He outlined the major open question: “Are inconsistencies in cesium vs. thallium measurements and vs. the predicted values in anapole moment analysis due to experimental error, interpretation error, or some other cause?”

He then discussed his research group’s investigations. Dounas-Frazer and the team at University of California, Berkeley sought to investigate these effects in another element and selected ytterbium because of its size and the fact that it has five stable isotopes. The experiment vaporized the element and analyzed the vapor.

The team found a result in 2010 which seemed fairly reasonable but had an error around 12 percent. Dounas-Frazer explained that analysis of the main quantities of interest requires error much less than one percent. The group has therefore spent two years scaling down the error and preparing a cross-check for the experiment. Their next goal is to determine isotope ratios and examine the neutron skin of ytterbium.