Abstract
A search for deeply bound ${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$ states in heavy nuclei was undertaken using the pion-transfer $^{208}\mathrm{Pb}$(n,p) reaction at the TRIUMF CHARGEX facility. Monoenergetic 418-MeV neutrons from the $^{7}\mathrm{Li}$(p,n) reaction were used to induce (n,p) reactions on a segmented $^{208}\mathrm{Pb}$ 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 \ensuremath{\approxeq}0.8 mb/sr MeV. This resulted in an upper limit of 0.35 mb/sr for the production cross section of ${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$ bound states in $^{208}\mathrm{Pb}$. 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.
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