A possible observation of $\Lambda $nn continuum structure and a bound $\Sigma $NN state using the (e,e'K$^{\mathrm{+}})$ reaction.

A mass spectroscopy experiment with a pair of nearly identical high resolution spectrometers and a tritium target was performed in Hall A at Jefferson Lab. Utilizing the (e,e'K$^{\mathrm{+}})$ reaction, two possible $\Lambda $nn resonance states and a bound $\Sigma $NN state were observed for the first time with an energy resolution of better than 1.6 MeV (FWHM), although greater statistics are needed to make definitive identifications. The energy resolution is the best ever reported for reaction mass spectroscopy involving A $=$ 3 hypernuclei. The experimentally measured $\Lambda $nn states can provide constraints in describing the $\Lambda $n interaction, for which no scattering data exist. Moreover, although bound A $=$ 3 and 4 $\Sigma $ hypernuclei have been predicted, only an A $=$ 4 $\Sigma $ hypernucleus ($^{\mathrm{4}}_{\mathrm{\Sigma }}$He) has been found, utilizing the (K$^{\mathrm{-}}$, $\pi^{\mathrm{-}})$ reaction on a He target. A possibility to study on a $\Sigma $NN bound is also discussed and the observed state in this experiment is likely to be a $\Sigma ^{\mathrm{0}}$nn state. The experiment proves the uniqueness of the (e,e'K$^{\mathrm{+}})$ reaction with the Tritium target using the CEBAF beam. The experiment needs to be repeated again with the optimized experimental configuration in order to achieve the needed statistics that is necessary to make solid confirmation and obtain the needed precision on the measurement on the binding energy and natural width of these states.