We find a remarkable agreement of the excitation energy spectrum of the 208Pb(d,3He) reaction measured at Td=600 MeV near the π- production threshold with its theoretical prediction. Their comparison leads us to assign the distinct narrow peak observed at about 5 MeV below the threshold to the formation of bound pionic states π ⊗ 207Pb of the quasisubstitutional configurations (2p)π-(3p3/2,3p1/2)-1n . A small bump observed on the tail of the peak is assigned to the pionic 1s state. The binding energies (Bnl) and the widths (Γnl) of the pionic orbitals are deduced to be B2p=5.13±0.02 (stat)±0.12 (syst) MeV and Γ2p = 0.43±0.06 (stat) ±0.06 (syst) MeV by decomposing the experimental spectrum into the pionic 1s and 2p components. While B2p and Γ2p are determined with small ambiguity, B2p and Γ2p are strongly correlated with each other, and are affected by the relative 1 s/2p cross section ratio assumed, since the 1s component is observed only as an unresolved bump. Thus, we have to allow large uncertainties 6.6 MeV<;B1s<6.9 MeV and 0.4 MeV<Γ1s <1.2 MeV. The experimental binding energies and widths are compared with theoretically calculated values based on various optical potential parameter sets, and are jointly used to deduce the effective π- mass in the nuclear medium.
|Number of pages
|Physical Review C - Nuclear Physics
|Published - 2000 Aug