Study of the $nn\Lambda$ State and $\Lambda n$ Interaction at Jefferson Lab

Abstract

An $nn\Lambda$, which consists of two neutrons and a Lambda hyperon, is a multi-baryon system with no charge. Studying the $nn\Lambda$ state would provide information about the $\Lambda n$ interaction which has not been directly measured by a scattering experiment. The experiment (E12-17-003) was performed in order to search for the $nn\Lambda$ state at Jefferson Lab. The $nn\Lambda$ is expected to be produced by the $(e,e'K^+)$ reaction, which has sensitivity to both bound and resonance states if the natural width of the $nn\Lambda$ is narrow enough to be observed as a peak. The experiment used gas targets of hydrogen and tritium for mass calibration and the $nn\Lambda$ production, respectively. The mass calibration with $\mathrm{H}(e,e'K^+) \Lambda /\Sigma ^0$ reactions gave the mass resolution of the $\Lambda$ and $\Sigma ^0$ each 3.5 $\mathrm{MeV}/c^2$ FWHM, for the elementary reaction. A spectrum of $\mathrm{^3 H}(e,e'K^+)X$ was obtained, and a simple model with a $\Lambda n$ final state interaction was applied to reproduce the spectrum.