The A(K−stop,π±Σ∓)A' reaction on p-shell nuclei

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 DAPHNE φ-factory (LNF-INFN, Italy).