Extracting the σ -term from low-energy pion-nucleon scattering

We present an extraction of the pion-nucleon ( π N ) scattering lengths from low-energy π N scattering, by fitting a representation based on Roy–Steiner equations to the low-energy data base. We show that the resulting values confirm the scattering-length determination from pionic atoms, and discuss the stability of the fit results regarding electromagnetic corrections and experimental normalization uncertainties in detail. Our results provide further evidence for a large π N σ -term, σ π N = 58 ( 5 ) MeV , in agreement with, albeit less precise than, the determination from pionic atoms.