The Violation of Reflection Symmetries in the Laws of Atomic Physics

Abstract

In discussing the degrees of symmetry of physical laws, it is useful to divide the interactions of physics into three categories: strong interactions, which include those between nucleons and between nucleons and mesons; electromagnetic interactions, of medium strength, which are also responsible for the outer shell of the atom; and weak interactions, to which category belong all the phenomena of beta-radioactivity associated with the emission or absorption of neutrinos, as well as the decay of Λ- and K-mesons, in which neutrinos are not involved.

From Experientia 14, 1–5 (1958).

The reflections of charge (C), space-coordinates (P) and time (T) and, particularly in connection with the space reflection, the distinction between polar vector and axial vector, scalar and pseudoscalar products are explained. The three different kinds of strong, medium (electromagnetic) and weak interactions are introduced. While the first two of them fulfil all reflection invariances mentioned separately, Lee and Yang showed (1956) that for the weak interactions no sufficient empirical evidence existed for the reflection invariances, and they also suggested experiments for checking them. The qualitative aspect of the experimental results available in November 1957, which show the violation of the C and the P invariance for weak interactions, is reviewed. The methods here applied are beta-decay of oriented nuclei, polarisation of emitted electrons in beta-decay, beta-gamma correlation, asymmetry in the decay of µ-mesons generated by π-meson-decay. The solution of the θ-τ-puzzle by the assumption of a single particle (K-meson) without defined parity is mentioned. In the concluding section some aspects of the unsolved theoretical problems of the deeper reasons for the symmetry violations of the weak interactions are briefly discussed which will possibly also lead into open cosmological questions.*