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 Li-6 and C-12 have been measured with 1% resolution. The C-12 spectrum is smooth whereas for Li-6 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 K-nuclear state. The peak is correlated with a pi(-) coming from Sigma(-) decay in flight, selected by setting the pi momentum larger than 275 MeV/c. The Sigma(-) could be produced, together with a 500 MeV/c proton, by the capture of a K- in a deuteron-cluster substructure of the Li-6 nucleus. The capture rate for such a reaction is (1.62 +/- 0.23stat(-0.44)(+0.71)(sys))%/K-stop(-), in agreement with the existing observations on stop, targets and with the hypothesis that the Li-6 nucleus can be interpreted as a (d + alpha) cluster.