Theoretical analysis on the $K^{-} {}^{3} \text{He} \to \Lambda p n$ reaction for the $\bar{K} N N$ bound-state search in the J-PARC E15 experiment

TL;DR

This paper provides a theoretical analysis of the $K^{-} {}^{3} ext{He} o \Lambda p n$ reaction, predicting two peaks in the invariant-mass spectrum that could indicate the $ar{K} N N$ bound state in the J-PARC E15 experiment.

Contribution

It introduces a theoretical framework to identify the $ar{K} N N$ bound state via the $ ext{He}^3(K^-, \Lambda p n)$ reaction, highlighting the significance of detecting a forward neutron.

Findings

Two peaks predicted in the $\Lambda p$ invariant-mass spectrum.

The lower peak corresponds to the $ar{K} N N$ bound state.

The higher peak results from kinematic effects.

Abstract

We theoretically analyze the $K^{-} {}^{3} \text{He} \to \Lambda p n$ reaction for the $\bar{K} N N$ bound-state search in the J-PARC E15 experiment. We find that, by detecting a fast and forward neutron in the final state, an almost on-shell $\bar{K}$ is guaranteed, which is essential to make a bound state with two nucleons from ${}^{3} \text{He}$. Then, this almost on-shell $\bar{K}$ can bring a signal of the $\bar{K} N N$ bound state in the $\Lambda p$ invariant-mass spectrum, although it inevitably brings a kinematic peak above the $\bar{K} N N$ threshold as well. As a consequence, we predict two peaks across the $\bar{K} N N$ threshold in the spectrum: the lower peak coming from the $\bar{K} N N$ bound state, and the higher one originating from the kinematics.