Search for Optical Rotation Induced by the Weak Neutral Current

Abstract

It is now clear that laser experiments on atoms can provide important information on one of the most crucial questions of elementary particle physics — the validity or otherwise of the unification of the weak and electromagnetic interactions in a single unified theory. The majority of the schemes put forward to date, and in particular the most basic and economical of them, the Weinberg-Salam [1, 2] model, predict the existence of additional weak interactions between the particles, electrons, protons and neutrons which make up an atom. These interactions are of order G_F the normal weak interaction coupling constant and therefore very weak since in atomic units, (e = ħ = m_e = 1), G_F = 2 × 10⁻¹⁴. At first sight this small value would seem to rule out any possibility of an atomic experiment since it is clearly impossible to make a direct comparison between experiment and theory at the i part in 10⁻¹⁴ level. But this neglects the fact that the weak interaction violates parity while the electromagnetic interaction conserves it, and it may be possible to devise an experiment to look for a very small explicitly parity violating effect in the presence of a very much larger parity conserving background.