Formation of the Multineutron Systems \({}^{{2}}{n}\) and \({}^{{3}}{n}\) in the Reactions of Stopped Pion Absorption

The formation of the multineutron systems \({}^{2}n\) and \({}^{3}n\) was studied in the reactions of stopped pion absorption by \({}^{9}\)Be nuclei. Measurements were carried out at low energy pion channel of LANL using two-arm multilayer semiconductor spectrometer. The bound states of \({}^{2}n\) and \({}^{3}n\) have not been found. In the missing mass spectrum of the reaction \({}^{9}\)Be(\(\pi^{-}\), \(t^{4}\)He), a peak was observed near the threshold, which is due to the formation of the \(s\)-wave virtual state of the dineutron. Indications of the existence of two states of the \({}^{3}n\) with resonant energies (\(E_{r}\approx 6\) MeV, and \({\approx}14\) MeV) were first obtained in the reactions \({}^{9}\)Be(\(\pi^{-}\), \(d^{4}\)He) and \({}^{9}\)Be(\(\pi^{-}\), \(t^{3}\)He). Comparison with theoretical and experimental results obtained by other authors was performed.