Deeply Bound $1\mathit{s}$ and $2\mathit{p}$ Pionic States in ${}_{}{}^{205}{}_{}{}^{}Pb$ and Determination of the $\mathit{s}$-Wave Part of the Pion-Nucleus Interaction

We observed well-separated $1s$ and $2p$ ${\pi }^{-}$ states in ${}^{205}\mathrm{Pb}$ in the ${}^{206}\mathrm{Pb}\left({d,}^3\mathrm{He}\right)$ reaction at $T_d=604.3\mathrm{}\mathrm{MeV}$. The binding energies and the widths determined are $B_{1s}=6.762\mathrm{}\pm 0.061\mathrm{MeV}$, ${\Gamma }_{1s}={0.764}_{-0.154\mathrm{}}^{+0.171\mathrm{}}\mathrm{MeV}$, $B_{2p}=5.110\mathrm{}\pm 0.045\mathrm{MeV}$, and ${\Gamma }_{2p}{=0.321\mathrm{}}_{-0.062\mathrm{}}^{+0.060\mathrm{}}\mathrm{MeV}$. They are used to deduce the real and imaginary strengths of the $s$-wave part of the pion-nucleus interaction, which translates into a positive mass shift of ${\pi }^{-}$ in ${}^{205}\mathrm{Pb}$.