A study of the proton spectra following the capture of K− in 6Li and 12C with FINUDA

Momenta spectra of protons emitted following the capture of K− in 6Li and 12C have been measured with 1% resolution. The 12C spectrum is smooth whereas for 6Li 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 -nuclear state. The peak is correlated with a π− coming from Σ− decay in flight, selected by setting the π momentum larger than 275 MeV/c. The Σ− could be produced, together with a 500 MeV/c proton, by the capture of a K− in a deuteron-cluster substructure of the 6Li nucleus. The capture rate for such a reaction is , in agreement with the existing observations on 4He targets and with the hypothesis that the 6Li nucleus can be interpreted as a (d+α) cluster.