The cross-section measurement for the $^3{\textrm H}(e,e'K^+)nn\Lambda$ reaction

TL;DR

This study conducted a high-sensitivity search for the hypothesized bound $nn ext{Lambda}$ hypernucleus via electron-induced reactions, setting upper limits on its production cross-section and contributing to the understanding of hypernuclear existence.

Contribution

The paper presents the first high-precision measurement of the $^3{ extrm{H}}( ext{e}, ext{e}'K^+)$ reaction cross-section, improving sensitivity and establishing upper limits for the $nn ext{Lambda}$ state.

Findings

No significant $nn ext{Lambda}$ signals observed.

Upper limits on production cross-section set at 21 and 31 nb/sr.

Results constrain theoretical models of hypernuclear states.

Abstract

The small binding energy of the hypertrition leads to predictions of non-existence of bound hypernuclei for isotriplet three-body systems such as $nn\Lambda$. However, invariant mass spectroscopy at GSI has reported events that may be interpreted as the bound $nn\Lambda$ state. The $nn\Lambda$ state was sought by missing-mass spectroscopy via the $(e,e'K^+)$ reaction at Jefferson Lab's experimental Hall A. The present experiment has higher sensitivity to the $nn\Lambda$-state investigation in terms of better precision by a factor of about three. The analysis shown in this article focuses on the derivation of the reaction cross-section for the $^3{\rm{H}}(\gamma^{*},K^+)\textrm{X}$ reaction. Events that were detected in an acceptance, where a Monte Carlo simulation could reproduce the data well ($|\delta p/p| < 4\%$), were analyzed to minimize the systematic uncertainty. No significant structures were observed with the acceptance cuts, and the upper limits of the production cross-section of the $nn\Lambda$ state were obtained to be $21$ and $31~\rm{nb/sr}$ at the $90\%$ confidence level when theoretical predictions of $(-B_{\Lambda}, \Gamma) = (0.25,0.8)$ and $(0.55, 4.7)$ MeV, respectively, were assumed. The cross-section result provides valuable information for examining the existence of $nn\Lambda$.