Jun 2 – 7, 2019
Carnegie Mellon University
America/New_York timezone

The pion-nucleon sigma term from pionic atoms

Jun 3, 2019, 1:30 PM
Rangos 1

Rangos 1

Contributed Meson-Nucleon Interactions Meson-Nucleon Interactions


Avraham Gal


Large scale fits to pionic atoms data show that the in-medium pion-nucleon
isovector scattering length b1 gets renormalized in pionic atoms by 30-40%
away from its free-space value [1], apparently owing to the decrease of the
pion decay constant in the nuclear medium in terms of the pion-nucleon sigma
term [2]. Accepting the validity of this approach, we extracted this sigma
term from a large-scale fit of pionic-atom level shift and width data across
the periodic table [3]. Our fitted value sigma=57+/-7 MeV is robust against
variation of pion-nucleon interaction terms other than the isovector s-wave
term with which sigma is associated. Higher order corrections to the leading
order in density involve some cancelations, suggesting thereby only a few
percent overall systematic uncertainty. The derived value of sigma agrees
with values obtained in several recent studies based on near-threshold
pion-nucleon phenomenology [4], but sharply disagrees with values obtained
in recent direct lattice QCD calculations [5].

[1] E. Friedman and A. Gal, Phys. Rep. 452 (2007) 89.
[2] W. Weise, Acta Phys. Polon B 31 (2000) 2715.
[3] E. Friedman, A. Gal, submitted to PLB, http://arXiv.org/abs/1901.03130
[4] J. Ruiz de Elvira et al., JPG 45 (2018) 024001.
[5] N. Yamanaka et al. (JLQCD Collaboration), PRD 98 (2018) 054516.

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