The $A(K_{stop}^{-},{\pi }^{\pm }{\mathrm{\Sigma }}^{\mp })A^{\mathrm{\prime }}$ reaction on p-shell nuclei

This letter is concerned with the study of the $K^-{stop}A\rightarrow \pi^\pm\Sigma^\mp A’$reactioninp-shellnuclei,i\mathrm{.}e\mathrm{.},$^{6,7}Li$,$^9Be$,$^{13}C$and$^{16}O$\mathrm{.}The$\pi^\pm\Sigma^\mp / K^-{stop}$ emission rates are reported as a function of $A$. These rates are discussed in comparison with previous findings. The ratio ${\pi }^{-}{\mathrm{\Sigma }}^{+}\mathrm{/}{\pi }^{+}{\mathrm{\Sigma }}^{-}$ 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 $\mathrm{\Lambda }(1405)$. The continuum momentum spectra of prompt pions and free sigmas are also discussed as well as the ${\pi }^{\pm }{\mathrm{\Sigma }}^{\mp }$ missing mass behavior and the link with the reaction mechanism. The apparatus used for the investigation is the FINUDA spectrometer operating at the DA$\mathrm{\Phi }$NE $\varphi$-factory (LNF-INFN, Italy).