Deeply bound 1s and 2p pionic states in 205Pb and effective pion mass in nuclear matter.

We have succeeded in observing the is and 2p bound pionic states in [sup 205]Pb nucleus as well separated peaks in the excitation spectrum of the [sup 206]Pb(d, [sup 3]He) reaction. The observed spectrum agreed quite well with the theoretical prediction where the formation cross section was calculated for the deeply bound pionic states. These states are accommodated in proximity to the nuclear surface as halo states in a potential provided by the attractive Coulomb and the repulsive core. The binding energies and the widths were precisely determined, and the values were used to deduce the unknown s-wave part of the π-nucleus interaction and to translate it to the effective pion mass in nuclear matter. [ABSTRACT FROM AUTHOR]