$K^- N$ amplitudes below threshold constrained by multinucleon absorption

Abstract

Six widely different subthreshold $K^- N$ scattering amplitudes obtained in SU(3) chiral-model EFT approaches by fitting to low-energy and threshold data are employed in optical-potential studies of kaonic atoms. Phenomenological terms representing $K^-$ multinucleon interactions are added to the EFT inspired single-nucleon part of the $K^-$-nucleus optical potential in order to obtain good fits to kaonic-atom strong-interaction level shifts and widths across the periodic table. Introducing as a further constraint the fractions of single-nucleon $K^-$ absorption at rest from old bubble-chamber experiments, it is found that only two of the models considered here reproduce these absorption fractions. Within these two models, the interplay between single-nucleon and multinucleon $K^-$ interactions explains features observed previously with fully phenomenological optical potentials. Radial sensitivities of kaonic atom observables are also re-examined, and remarks are made on the role of `subthreshold kinematics' in absorption at rest calculations.