Clarifications on the Chien-Shiung Wu feature

In the fascinating article “Chien-Shiung Wu’s trailblazing experiments in particle physics ” (Physics Today, December 2024, page 28), the authors incorrectly describe the result of an experiment testing a prediction by John Wheeler. ¹ They report that Ernst Bleuler and Helmut Bradt at Purdue University measured the ratio of perpendicular to parallel polarization of gamma rays emitted from the decay of an electron–positron pair as 2.1 ± 0.64, a relatively large uncertainty. That ratio was for one run; the published result combining all of their measurements was actually a much more respectable 1.9 ± 0.3. ² Given that Wheeler predicted a maximum ratio of 1.100 and later theorists ^{3 , 4} fixed the error and calculated a ratio of 1.7 for the configuration used by Bleuler and Bradt, the two could at least be given credit for showing that Wheeler’s math was wrong and that the new predictions were pretty good.

By adroitly utilizing the latest in scintillation detector technology instead of Geiger counters, Wu and her graduate student Irving Shaknov ⁵ obtained 2.04 ± 0.08, where the improved theory predicted 2.00 for their configuration. The scientific community accepted this as confirmation of Wheeler’s suggestion that the electron–positron pairs decay from a state with zero angular momentum. Wheeler makes no mention of entanglement, whose significance became apparent much later.