Search For Deeply Bound Pionic States In Pb-208 Using The Pb-208(N,P) Reaction At Tn=418 Mev

A search for deeply bound pi- states in heavy nuclei was undertaken using the pion-transfer Pb-208(n,p) reaction at the TRIUMF CHARGEX facility. Monoenergetic 418-MeV neutrons from the 7Li(p,n) reaction were used to induce (n,p) reactions on a segmented Pb-208 target. The spectrum between 100- and 180-MeV excitation energy was measured with an energy resolution of 1.15 MeV (FWHM). In the region of 120-140 MeV, where the deeply bound pionic states were expected, the observed spectrum exhibited a smooth continuumlike behavior with a cross section of almost-equal-to 0.8 mb/sr MeV. This resulted in an upper limit of 0.35 mb/sr for the production cross section of pi- bound states in Pb-208. This cross section is substantially smaller than the estimate based on the plane-wave impulse approximation, showing the importance of the effect of distortion. The distortion effect is calculated and discussed.