Role of chiral two-body currents in $^6$Li magnetic properties in light of a new precision measurement with the relative self-absorption technique

A direct measurement of the decay width of the first excited $0^+$ state of $^6$Li using the relative self-absorption technique is reported. Our value of $\Gamma_{\gamma, 0^+_1 \to 1^+_1} = 8.17(14)_{\mathrm{stat.}} (11)_{\mathrm{syst.}}$ eV provides sufficiently low experimental uncertainties to test modern theories of nuclear forces and resolve a long-standing ambiguity in the literature. The corresponding transition rate is compared to ab initio calculations based on chiral effective field theory that take into account contributions to the magnetic dipole operator beyond leading order. This enables a precision test of the impact of two-body currents that enter at next-to-leading order.