Decay of K mesons as a test of the universal Fermi interaction

Abstract

On the basis of current experimental evidence, there is no distinction between µ mesons and electrons other than a difference in rest mass. Electromagnetic interactions are identical since electrons and µ mesons have the same charge, and the hypothesis of a universal Fermi interaction, which asserts that they couple in exactly the same way in the weak interactions, has received considerable support by comparing β-decay phenomena with the decay of free µ mesons and µ capture in nuclei. An at least equally fruitful series of experiments for reassuring one about the validity of the universal interaction idea is the analysis of the decays of µ and K mesons into electrons and µ mesons. The details of such individual decays are not easily obtained theoretically, since they presumably involve strongly coupled virtual particles; however, the ratio of decay rates into electron modes and µ-meson modes may often be calculated exactly with no assumptions beyond saying that the weak interaction is local and may be treated in first order, and that the weak interaction is the same for electrons and µ mesons.(1)