This letter is concerned with the study of the $K^-_{stop}Arightarrow pi^pmSigma^mp A$ reaction in p-shell nuclei, i.e., $^{6,7}Li$, $^9Be$, $^{13}C$ and $^{16}O$. The $pi^pmSigma^mp / K^-_{stop}$ emission rates are reported as a function of $A$. The
se rates are discussed in comparison with previous findings. The ratio $pi^-Sigma^+/pi^+Sigma^-$ 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 $Lambda(1405)$. The continuum momentum spectra of prompt pions and free sigmas are also discussed as well as the $pi^pmSigma^mp$ missing mass behavior and the link with the reaction mechanism. The apparatus used for the investigation is the FINUDA spectrometer operating at the DA$Phi$NE $phi$-factory (LNF-INFN, Italy).
The FINUDA experiment collected data to study the production of hypernuclei on different nuclear targets. The hypernucleus formation occurred through the strangeness-exchange reaction $K^-_{stop} + ; ^AZ rightarrow ; ^A_{Lambda}Z + pi^-$. From the an
alysis of the momentum of the emerging $pi^-$, binding energies and formation probabilities of $^7_{Lambda}$Li, $^9_{Lambda}$Be, $^{13}_{Lambda}$C and $^{16}_{Lambda}$O have been measured and are here presented. The behavior of the formation probability as a function of the atomic mass number A is also discussed.
The Non-Mesonic (NM) decay of $^4_Lambda{mathrm{He}}$ and $^5_Lambda{mathrm{He}}$ in two-body channels has been studied by the FINUDA Collaboration. Two-body NM decays of hypernuclei are rare and the existing observations and theoretical calculations
are scarce. The $^4_Lambda{mathrm{He}}rightarrow d+d,; p+t$ decay channels simultaneously observed by FINUDA on several nuclei are compared: the $pt$ channel is the dominant one. The decay yields for the two decay channels are assessed for the first time: they are $(1.37pm 0.37)times 10^{-5}/K^-_{stop}$ and $(8.3pm 1.0)times 10^{-5}/K^-_{stop}$, respectively. Due to the capability of FINUDA of identifying $^5_Lambda{mathrm{He}}$ hypernuclei, a few $^5_Lambda{mathrm{He}}rightarrow d+t$ decay events have also been observed. The branching ratio for this decay channel has been measured for the first time: $(3.0pm 2.3)times 10^{-3}$.
The FINUDA experiment performed a systematic study of the charged mesonic weak decay channel of $p$-shell $Lambda$-hypernuclei. Negatively charged pion spectra from mesonic decay were measured with magnetic analysis for the first time for ${^{7}_{Lam
bda}Li}$, ${^{9}_{Lambda}Be}$, ${^{11}_{Lambda}B}$ and ${^{15}_{Lambda}N}$. The shape of the $pi^{-}$ spectra was interpreted through a comparison with pion distorted wave calculations that take into account the structure of both hypernucleus and daughter nucleus. Branching ratios $Gamma_{pi^{-}}/Gamma_{tot}$ were derived from the measured spectra and converted to $pi^{-}$ decay rates $Gamma_{pi^{-}}$ by means of known or extrapolated total decay widths $Gamma_{tot}$ of $p$-shell $Lambda$-hypernuclei. Based on these measurements, the spin-parity assignment $1/2^+$ for ${^{7}_{Lambda}Li}$ and $5/2^+$ for ${^{11}_{Lambda}B}$ ground-state are confirmed and a spin-parity $3/2^+$ for ${^{15}_{Lambda}N}$ ground-state is assigned for the first time.
