Deeply Bound 1s And 2p Pionic States In Pb-205 And Determination Of The S-Wave Part Of The Pion-Nucleus Interaction

We observed well-separated 1s and 2p pi(-) states in Pb-205 in the Pb-206(d, He-3) reaction at T-d = 604.3 MeV. The binding energies and the widths determined are B-1s = 6.762 +/- 0.061 MeV, Gamma(1s) = 0.764 (1+0.171)(-0.154) MeV, B-2p = 5.110 +/- 0.045 MeV, and Gamma(2p) = 0.321(-0.062)(+0.060) 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 Pb-205.