This Letter is concerned with the study of the K−
stop A→π±
Σ
∓ A reaction in p-shell nuclei, i.e., 6,7Li, 9Be,
13C and 16O. The π±
Σ
∓
/K−
stop emission rates are reported as a function of A. These rates are discussed in
comparison with previous findings. The ratio π−
Σ
+
/π+
Σ
− in p-shell nuclei is found to depart largely
from that on hydrogen, which provides support for large in-medium effects possibly generated by the
sub-threshold Λ(1405). The continuum momentum spectra of prompt pions and free sigmas are also
discussed as well as the π±
Σ
∓ missing mass behavior and the link with the reaction mechanism. The
apparatus used for the investigation is the FINUDA spectrometer operating at the DANE φ-factory (LNFINFN,
Italy).
