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arXiv · 2008.03147

Extracting $\sigma_{\pi N}$ from pionic atoms

Eliahu Friedman·Avraham Gal
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Abstract

We discuss a recent extraction of the $\pi N$ $\sigma$ term $\sigma_{\pi N}$ from a large-scale fit of pionic-atom strong-interaction data across the periodic table. The value thus derived, $\sigma_{\pi N}^{\rm FG}=57\pm 7$ MeV, is directly connected via the Gell-Mann--Oakes--Renner expression to the medium-renormalized $\pi N$ isovector scattering amplitude near threshold. It compares well with the value derived recently by the Bern-Bonn-J\"{u}lich group, $\sigma_{\pi N}^{\rm RS}=58\pm 5$ MeV, using the Roy-Steiner equations to control the extrapolation of the vanishingly small near threshold $\pi N$ isoscalar scattering amplitude to zero pion mass.

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Eliahu Friedman, Avraham Gal. 2020-08-07. Extracting $\sigma_{\pi N}$ from pionic atoms. https://doi.org/10.5506/aphyspolb.51.45%2010.1063%2F5.0008577

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