The pion-nucleon Sigma term is definitely large: results from a G.W.U. analysis of pion nucleon scattering data

TL;DR

This paper presents a new, larger estimate of the pion-nucleon Sigma term based on recent scattering data, challenging previous canonical values and implications for nucleon strangeness.

Contribution

The study provides a revised Sigma term value of 79±7 MeV using a comprehensive analysis of pion-nucleon scattering data, including systematic effects and recent experimental inputs.

Findings

Sigma value is significantly larger than previous estimates.

Large Sigma implies a high nucleon strangeness fraction, questioning current interpretations.

Results are robust against various systematic uncertainties.

Abstract

A new result for the pion nucleon Sigma term from a George Washington University/TRIUMF group analysis of pion nucleon data is presented. The value Sigma=79$\pm$7 MeV was obtained, compared to the canonical value 64$\pm$8 MeV found by Koch. The difference is explained simply by the PSI pionic hydrogen value for a(pi -p), the latest results for the $\pi NN$ coupling onstant, and a narrower Delta resonance. Many systematic effects have been investigated, including Coulomb corrections, and database changes, and our results are found to be robust. In the standard interpretation, our value of Sigma implies a nucleon strangeness fraction y/2~0.23. The implausibility of such a large strange component suggests that the relationship between Sigma and nucleon strangeness ought to be re-examined.