A study of the proton spectra following the capture of $K^{-}$ in ${}^6$Li and ${}^{12}$C with FINUDA

Abstract

Momenta spectra of protons emitted following the capture of $K^{-}$ in ${}^6$Li and ${}^{12}$C have been measured with 1% resolution. The ${}^{12}$C spectrum is smooth whereas for ${}^6$Li a well defined peak appears at about 500 MeV/$c$. The first observation of a structure in this region was identified as a strange tribaryon or, possibly, a $\bar{K}$-nuclear state. The peak is correlated with a $\ddot{I}{€}^{-}$ coming from $\hat{I}{\pounds }^{-}$ decay in flight, selected by setting momenta larger than 275 MeV/$c$. The $\hat{I}{\pounds }^{-}$ could be produced, together with a 500 MeV/$c$ proton, by the capture of a $K^{-}$ in a deuteron-cluster substructure of the ${}^6$Li nucleus. The capture rate for such a reaction is $(1.62\pm 0.23_{stat} ^{+0.71}_{-0.44}(sys))%/K^-_{stop}$, in agreement with the existing observations on ${}^4$He targets and with the hypothesis that the ${}^6$Li nucleus can be interpreted as a $(d+\hat{I}\pm )$ cluster.

21 pages, 10 figures. Accepted for publication in NPA