T. Yamazaki

Delayed annihilation of antiprotons stopped in liquid helium has been observed, revealing that about 3.6% of stopped antiprotons are trapped in long-lived metastable states. No delayed component was found either in liquid nitrogen or in liquid argon. The observed time distribution of delayed annihilation shows fast-decaying components followed by a major part with a decay time constant of 3 \ensuremath{\mu}sec.

We have analyzed data of the DISTO experiment on the exclusive $pp\ensuremath{\rightarrow}p\ensuremath{\Lambda}{K}^{+}$ reaction at 2.85 GeV to search for a strongly bound compact ${K}^{\ensuremath{-}}pp(\ensuremath{\equiv}X)$ state to be formed in the $pp\ensuremath{\rightarrow}{K}^{+}+X$ reaction. The observed spectra of the ${K}^{+}$ missing mass and the $p\ensuremath{\Lambda}$ invariant-mass with high transverse momenta of $p$ and ${K}^{+}$ revealed a broad distinct peak of $26\mathrm{\text{\ensuremath{-}}}\ensuremath{\sigma}$ confidence with a mass ${M}_{X}=2267\ifmmode\pm\else\textpm\fi{}3(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}5(\mathrm{syst})\text{ }\text{ }\mathrm{MeV}/{c}^{2}$ and a width ${\ensuremath{\Gamma}}_{X}=118\ifmmode\pm\else\textpm\fi{}8(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}10(\mathrm{syst})\text{ }\text{ }\mathrm{MeV}$. The enormously large cross section indicates formation of a compact ${K}^{\ensuremath{-}}pp$ with a large binding energy of ${B}_{K}=103\text{ }\text{ }\mathrm{MeV}$, which can be a possible gateway toward cold and dense kaonic nuclear matter.

Deeply bound $1s$ states of ${\ensuremath{\pi}}^{\ensuremath{-}}$ in $^{115,119,123}\mathrm{S}\mathrm{n}$ were preferentially observed using the $\mathrm{S}\mathrm{n}(d,^{3}\mathrm{H}\mathrm{e})$ pion-transfer reaction under the recoil-free condition. The $1s$ binding energies and widths were precisely determined and were used to deduce the isovector parameter of the $s$-wave pion-nucleus potential to be ${b}_{1}=\ensuremath{-}(0.115\ifmmode\pm\else\textpm\fi{}0.007){m}_{\ensuremath{\pi}}^{\ensuremath{-}1}$. The observed enhancement of $|{b}_{1}|$ over the free $\ensuremath{\pi}N$ value (${b}_{1}^{\mathrm{f}\mathrm{r}\mathrm{e}\mathrm{e}}/{b}_{1}=0.78\ifmmode\pm\else\textpm\fi{}0.05$) indicates a reduction of the chiral order parameter, ${f}_{\ensuremath{\pi}}^{*}(\ensuremath{\rho}{)}^{2}/{f}_{\ensuremath{\pi}}^{2}\ensuremath{\approx}0.64$, at the normal nuclear density, $\ensuremath{\rho}={\ensuremath{\rho}}_{0}$.