Level Shifts inK-Mesonic Atoms

A recent experiment on $K^{-}$ capture at rest on ${\mathrm{He}}^4$ failed to observe any perturbing effect upon the Coulomb levels of the $K$-mesonic atom from the $K^{-}$ nuclear interaction. This result was considered to be surprising because the $S$-wave $\overline{K}$-nucleon forces are known to be strong, at least in the isospin-zero channel. An attempt is made to explain the apparent weakness of the $K^{-}{\mathrm{He}}^3$ forces by a Born-Oppenheimer estimate of the effective potential. The result contains the range of the $\overline{K}-\mathrm{N}$ force as an undetermined parameter; an upper bound is obtained from the result of the $K^{-}-{\mathrm{He}}^4$ experiment. Predictions (upper bounds) are then made for other very light nuclei.