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 Kˉ-nuclear state. The peak is correlated with a
π− coming from Σ− decay in flight, selected by setting momenta
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 (1.62\pm
0.23_{stat} ^{+0.71}_{-0.44}(sys))%/K^-_{stop}, 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.Comment: 21 pages, 10 figures. Accepted for publication in NP