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

TL;DR

This study constrains $K^- N$ scattering amplitudes below threshold using chiral-model EFT approaches and incorporates multinucleon interactions to accurately describe kaonic atom data, revealing model dependencies and the importance of subthreshold kinematics.

Contribution

It introduces a method to constrain subthreshold $K^- N$ amplitudes by combining EFT-based scattering data with phenomenological multinucleon interactions and absorption fractions.

Findings

Only two models reproduce absorption fractions from experiments.

Interplay between single- and multinucleon interactions explains previous phenomenological results.

Radial sensitivities and subthreshold kinematics are important in absorption calculations.

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.