Two-body current contribution toM1transitions and moments inCl38andK40

We deduce evidence for the existence of a two-body current contribution to $M1\mathrm{}$ transitions and moments in nuclei, based on the application of shell model theory to experimental data. A complete specification of a two-body $M1\mathrm{}$ operator, within a shell-model configuration, can be obtained by combining data from particle-particle and particle-hole nuclei. For this purpose, new particle-hole relations are derived for $M1\mathrm{}$ transitions. The method of analysis is applied to the particle-hole pair ${}_{}{}^{38}{}_{}{}^{}\mathrm{Cl}$-${}_{}{}^{40}{}_{}{}^{}\mathrm{K}$. The two-body current contributions could be effects of either configuration mixing, or mesonic currents, or both.