Atomic Parity Experiment Has Its Moment

For over eight years, researchers at JILA and the University of Colorado, Boulder, have worked patiently and painstakingly to improve the precision with which they can detect a rare, parity‐violating atomic transition. The group, led by Carl Wieman, has finally been rewarded with a measurement of the transition amplitude that is precise to 0.35%, a factor of seven better than their 1988 measurement of the same transition. The dominant uncertainty in the value of this term is now the uncertainty in the atomic theory, which reached 1.2% in the early 1990s. The combined uncertainties bring the data into the realm where they place useful constraints on the Standard Model of electro weak interactions. As icing on the cake, the Boulder experiment also gives the first good evidence for a nuclear feature predicted years ago: the nuclear anapole moment.