At the Mainz Microtron MAMI, the first high-resolution pion spectroscopy from decays of strange systems was performed by electron scattering off a ${}^9\mathrm{Be}$ target in order to study the $\mathrm{\Lambda }$ binding energy of light hypernuclei. Positively charged kaons were detected by a short-orbit spectrometer with a broad momentum acceptance at 0° forward angles with respect to the beam, efficiently tagging the production of strangeness in the target nucleus. Coincidentally, negatively charged decay pions were detected by two independent high-resolution spectrometers. About ${10}^3$ pionic weak decays of hyperfragments and hyperons were observed. The pion momentum distribution shows a monochromatic peak at $p_{\pi }\approx 133\mathrm{MeV}/c$, corresponding to the unique signature for the two-body decay of hyperhydrogen ${}_{\mathrm{\Lambda }}{}^4\mathrm{H}\to {}^4\mathrm{He}+{\pi }^{-}$, stopped inside the target. Its $\mathrm{\Lambda }$ binding energy was determined to be $B_{\mathrm{\Lambda }}=2.12\pm 0.01(\text{stat})\pm 0.09(\text{syst})\mathrm{MeV}$ with respect to the ${}^3\mathrm{H}+\mathrm{\Lambda }$ mass.

The experimental data obtained from the reaction of ${}^6$Li projectiles at 2$A$ GeV on a fixed graphite target were analyzed to study the invariant mass distributions of $d+{\pi }^{-}$ and $t+{\pi }^{-}$. Indications of a signal in the $d+{\pi }^{-}$ and $t+{\pi }^{-}$ invariant mass distributions were observed with significances of 5.3 $\sigma$ and 5.0 $\sigma$, respectively, when including the production target, and 3.7 $\sigma$ and 5.2 $\sigma$, respectively, when excluding the target. The estimated mean values of the invariant mass for $d+{\pi }^{-}$ and $t+{\pi }^{-}$ signal were 2059.3 $\pm$ 1.3 $\pm$ 1.7 MeV/c${}^2$ and 2993.7 $\pm$ 1.3 $\pm$ 0.6 MeV/c${}^2$ respectively. The lifetime estimation of the possible bound states yielding to $d+{\pi }^{-}$ and $t+{\pi }^{-}$ final states were deduced to be as ${181}_{-24}^{+30}\pm 25$ ps and ${190}_{-35}^{+47}\pm 36$ ps, respectively. Those final states may be interpreted as the two-body and three-body decay modes of a neutral bound state of two neutrons and a $\Lambda$ hyperon, ${}_{\Lambda }^{3}n$.

Excitation spectra of ${}^{11}\mathrm{C}$ are measured in the ${}^{12}\mathrm{C}(p,d)$ reaction near the ${\eta }^{\prime }$ emission threshold. A proton beam extracted from the synchrotron SIS-18 at GSI with an incident energy of 2.5 GeV impinges on a carbon target. The momenta of deuterons emitted at 0° are precisely measured with the fragment separator (FRS) operated as a spectrometer. In contrast to theoretical predictions on the possible existence of deeply bound ${\eta }^{\prime }$-mesic states in carbon nuclei, no distinct structures are observed associated with the formation of bound states. The spectra are analyzed to set stringent constraints on the formation cross section and on the hitherto barely known ${\eta }^{\prime }$-nucleus interaction.