On the structure observed in the in-flight ${}^{3}\text{He} ( K^{-} , \, \Lambda p ) n$ reaction at J-PARC

TL;DR

This paper investigates the origin of a peak in the ${}^{3} ext{He} ( K^{-} , \, \Lambda p ) n$ reaction at J-PARC, providing evidence that it is due to a $ar{K} N N$ bound state rather than an uncorrelated $\\Lambda(1405) p$ system.

Contribution

The study offers a theoretical analysis distinguishing between two scenarios, supporting the formation of a $ar{K} N N$ bound state as the source of the observed peak.

Findings

The experimental peak is well reproduced by the $ar{K} N N$ bound state hypothesis.

The uncorrelated $\\Lambda(1405) p$ scenario is discarded.

Supports the existence of light kaonic nuclei.

Abstract

A theoretical investigation is done to clarify the origin of the peak structure observed near the $K^{-} p p$ threshold in the in-flight ${}^{3}\text{He} ( K^{-}, \, \Lambda p ) n$ reaction of the J-PARC E15 experiment, which could be a signal of the lightest kaonic nuclei, that is, the $\bar{K} N N (I=1/2)$ state. For the investigation, we evaluate the $\Lambda p$ invariant mass spectrum assuming two possible scenarios to interpret the experimental peak. One assumes that the $\Lambda (1405)$ resonance is generated after the emission of an energetic neutron from the absorption of the initial $K^-$, not forming a bound state with the remaining proton. This uncorrelated $\Lambda (1405) p$ system subsequently decays into the final $\Lambda p$. The other scenario implies that, after the emission of the energetic neutron, a $\bar{K} N N$ bound state is formed, decaying eventually into a $\Lambda p$ pair. Our results show that the experimental signal observed in the in-flight ${}^{3}\text{He} ( K^{-} , \, \Lambda p ) n$ reaction at J-PARC is qualitatively well reproduced by the assumption that a $\bar{K} N N$ bound state is generated in the reaction, definitely discarding the interpretation in terms of an uncorrelated $\Lambda (1405) p$ state.