Parity Non-Conservation in Atomic Bismuth

Abstract

Over the last year or so a number of developments have taken place in the search for parity non-conservation (PNC). in neutral weak current interactions both in atoms and in high energy physics experiments. Firstly, the recent announcement by(1) the S.L.A.C. group(1) that PNC has been detected in electron-proton and electron- deuteron scattering at energies around 20 GeV seems to support more or less unambiguously the Weinberg-Salam model(2) Secondly, new results have been obtained in the three atomic physics experiments working with bismuth vapour. In particular the Novosibirsk group(3) claim to have seen PNC at the level predicted by the Weinberg-Salam model (together with the atomic calculation of Novikov, Sushkov and Khriplovich(4)). The position is at present intriguing since experiments started several years ago at Oxford (648 nm transition in Bi) and Seattle (876 nm transition in Bi) and which were the first to reach the necessary sensitivity(5) have still failed to produce a result inconsistent with zero PNC. Thus a question mark still hangs over the atomic physics results, and the discrepancy between the Oxford and Novosibirsk results for the same atomic line must be resolved. It seems likely, however, that the situation will be clarified in the next few months as further refinements are made to the experiments with a corresponding reduction in the possible systematic error. Furthermore, experiments started more recently should also yield results(6).