I. Parity violation induced by weak neutral currents in atomic physics

Abstract

In this paper (the first of a series), we present a general analysis of the parity violating phenomena induced by neutral currents in Atomic Physics. We first give expressions for the short range parity violating electron-nucleus and electron-electron potentials predicted by the theoretical schemes of weak interactions featuring neutral currents. We turn next to a detailed computation of the matrix element, between one-particle s and p states, of the electron-nucleus parity violating potential. Using a non-trivial extension of a method used by Foldy to put on a more rigorous basis a formula of Fermi and Segre giving the wave function of an s valence electron at the nucleus, we arrive at a remarkably simple expression, in terms of the binding energies, with a small correcting term involving the interpolated quantum defect and the potential of the electronic cloud at the origin. Arguments are given which lead us to believe that the accuracy of our formula is comparable to that of the Fermi-Segre formula, i. e. a few per cent when Z >> 1. Besides its simplicity, a remarkable feature of our result is a Z3 dependence, which obviously favours heavy atoms. We give a brief analysis of the manifestation of parity mixing in atomic radiative transitions, with a particular emphasis on the implications of time reversal invariance, which is preserved by the interactions discussed in this paper. In order to improve the existing limits, we suggest looking for parity violating effects in twice forbidden magnetic dipole transitions induced by a tunable laser beam in heavy atoms. In a typical case, like the 6 S1/2 → 7 S1/2 transition in atomic Cesium, a circular dichroism of the order of 10-4 is predicted. Finally we discuss the apparently more remote possibilities offered by the muonic atoms.