Deeply bound 1s and 2p pionic states in 205Pb and determination of the s-wave part of the pion-nucleus interaction.

n at small momentum transfer. The observed spectrum in the previous experiment showed a distinct but skewed 2pp peak due to the presence of the 3p12 and 3p32 neutron hole states separated in energy by 0.90 MeV. The 1sp state was observed as a bump at the shoulder of the 2pp peak accordingly. In the present paper, we report on a new experiment using a 206 Pb target, which was purposely undertaken in view of the smaller contribution of the 3p12 hole and, consequently, a better separation of the 1sp and 2pp states. This expectation was supported by a theoretical study [10]. The experiment was performed with the Fragment Separator (FRS) [11] using a Td 604.3 MeV deuteron beam from the SIS-18 synchrotron at GSI, Darmstadt. The detailed description of the experimental procedures and analyses are found in Refs. [3,4,12]. The beam intensity was 1.5 3 10 11 spill at 1 s spill duration and 3 s cycle time. We employed a 1.5 mm wide and 25 mgcm 2 thick 206 Pb target. The 3 He momentum spectrum was measured at excitation energies covering the bound p 2 region.