ΣNNquasibound states inHe3(K−,π∓) reactions at 600 MeV/c

Abstract

We theoretically demonstrate the inclusive and semiexclusive spectra in the $^{3}\mathrm{He}$(${K}^{\ensuremath{-}}$, ${\ensuremath{\pi}}^{\ensuremath{\mp}}$) reactions at 600 MeV/$c$ (4${}^{\ensuremath{\circ}}$) within a distorted-wave impulse approximation, using a coupled ($2N\ensuremath{-}\ensuremath{\Lambda})+(2N\ensuremath{-}\ensuremath{\Sigma}$) model with a spreading potential. We present the possible existence of the $\ensuremath{\Sigma}\mathit{NN}$ quasibound state with ${J}^{\ensuremath{\pi}}=$ 1/2${}^{+}$, $T\ensuremath{\simeq}$ 1 near the $\ensuremath{\Sigma}$ threshold, predicted by a $2N\ensuremath{-}Y$ folding-model potential derived from $\mathit{YN}$ $g$-matrices. The result shows that a signal of the ${}_{\ensuremath{\Sigma}}^{3}$He quasibound state is clearly confirmed near the $\ensuremath{\Sigma}$ threshold in the ${\ensuremath{\pi}}^{\ensuremath{-}}$ spectrum, whereas a peak of the ${}_{\ensuremath{\Sigma}}^{3}n$ quasibound state is rather reduced in the ${\ensuremath{\pi}}^{+}$ spectrum owing to the interference effects caused by the ${}^{3}{S}_{1}$-${}^{1}{S}_{0}$ admixture in the $\mathit{NN}$ pair. The mechanism of $\ensuremath{\Sigma}$ production for these spectra and charge symmetry breaking effects are also discussed.