Intranuclear cascade calculation of pion-nucleus reactions in the resonance region

The predictions of the intranuclear cascade model are compared with experimental inclusive pion-nucleus inelastic scattering and absorption cross sections in the $\Delta$-resonance region as a function of bombarding energy and target mass and with the results of recent measurements of ($\pi , \pi p$) and (${\pi }^{+}, 2p$) for ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$ at $E_{\mathrm{lab}}=245\mathrm{}$ MeV in which the two outgoing particles were measured in coincidence. The calculations reproduce well the mass dependence of the inclusive cross sections; however, the calculated bombarding energy dependence is flatter for the inelastic cross section and more peaked for the absorption cross section than the experimental energy dependence. The calculations for ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ were made with two assumptions regarding the momentum distribution of the nucleons in the nucleus: (1) the "usual" local degenerate Fermi gas; (2) a momentum distribution based on an harmonic-oscillator shell model. The angular correlations for ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}({\pi }^{+}, {\pi }^{+}p)$ and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}({\pi }^{+}, 2p)$ are shown to provide a sensitive test for the momentum distribution, with the harmonic-oscillator shell model giving better agreement with the experimental results. The calculations show that multiple scattering of the pion and final state interactions of the outgoing proton contribute approximately equally to the nonquasifree part of the (${\pi }^{+}, {\pi }^{+}p$) cross section. The calculated number of nucleons $N$ taking part in the pion absorption process has a rather wide distribution which is generally peaked at the minimum number, $N=2\mathrm{}$. The calculated $\frac{({\pi }^{-}, {\pi }^{-}p)}{({\pi }^{+}, {\pi }^{+}p)}$ cross section ratio for the quasifree peak at 245 MeV is larger than the free ratio in contradiction with the experimental results. This may be an indication of coherent effects which are not included in the intranuclear cascade model.