Branching ratios of mesonic and nonmesonic antikaon absorptions in nuclear medium

TL;DR

This paper theoretically investigates the branching ratios of K^- meson absorption in nuclear matter, highlighting the dominance of Lambda(1405) contributions and comparing mesonic and nonmesonic absorption behaviors.

Contribution

It provides a detailed theoretical analysis of K^- absorption mechanisms in nuclei, emphasizing the role of Lambda(1405) and the effects of nuclear density and kaon momentum.

Findings

Mesonic absorption accounts for about 70% of K^- absorption at saturation density.

Nonmesonic absorption accounts for about 30%, with specific ratios among hyperon-nucleon channels.

Interference effects cause different branching ratios in pi Sigma channels, consistent with experiments.

Abstract

The branching ratios of K^- absorption at rest in nuclear matter are theoretically investigated in order to understand the mechanism of K^- absorption into nuclei. For this purpose mesonic and nonmesonic absorption potentials are evaluated as functions of nuclear density, the kaon momentum and energy from one- and two-body K^- self-energy, respectively. By using a chiral unitary approach for the s-wave Kbar N amplitude we find that both the mesonic and nonmesonic absorption potentials are dominated by the Lambda(1405) contributions. The fraction of the mesonic and nonmesonic absorptions are evaluated to be respectively about 70% and 30% at the saturation density almost independently on the kaon momentum. We also observe different behavior of the branching ratios to pi ^+ Sigma^- and pi^- Sigma^+ channels in mesonic absorption due to the interference between Lambda(1405) and the I=1 nonresonant background, which is consistent with experimental results. The nonmesonic absorption ratios [Lambda p]/[Sigma^0 p] and [Lambda n]/[Sigma^0 n] are about unity while [Sigma^+ n]/[Sigma^0 p] and [Sigma^- p]/[Sigma^0 n] are about two due to the Lambda(1405) dominance in absorption. Taking into account the kaon momenta and energies, the absorption potentials become weaker due to the downward shift of the initial K^-N two-body energy, but this does not drastirally change the nonmesonic fraction. The Sigma(1385) contribution in the p-wave Kbar N amplitude is examined and found to be very small compared to the Lambda(1405) contribution in slow K^- absorption.