Testing in-medium $\pi N$ dynamics on pionic atoms

Abstract

A general algorithm for handling the energy dependence of meson-nucleon amplitudes in the nuclear medium has been recently applied to antikaons and to eta mesons. Here we test this approach on $\pi N$ amplitudes in pionic atoms where direct comparison can be made with ample experimental results. Applying this algorithm to a large-scale fit of 100 pionic-atom data points across the periodic table, which also include the `deeply-bound' states in Sn and Pb, reaffirms earlier conclusions on the density-dependent renormalization of the $\pi N$ threshold isovector amplitude $b_1$, or equivalently the renormalization of the pion decay constant $f_{\pi}$ in the nuclear medium.