Σ− production spectrum in the inclusive (π−,K+) reaction on 209Bi and the Σ-nucleus potential

We investigate theoretically the Σ− hypernuclear production by the inclusive (π−,K+) reaction on a neutron-excess 209Bi target in the framework of a distorted wave impulse approximation with an optimal Fermi-averaging for the elementary π−+p→K++Σ− t-matrix. In order to study the Σ-nucleus potentials constructed with isoscalar and isovector components, we compare the calculated spectra of the 209Bi(π−,K+) reaction with the experimental data at KEK, using several Σ-nucleus (optical) potentials for Σ−–208Pb which are determined by fits to the Σ− atomic X-ray data. Our analysis confirms that the potentials having a repulsion inside the nuclear surface and an attraction outside the nucleus with a sizable absorption, can well reproduce the data. But it is still difficult to discriminate among the radial distributions of these potentials inside the heavy nucleus. The contribution of the isovector component in the potential is not determined uniquely by the 209Bi(π−,K+) spectrum.