Single-pion contribution to the Gerasimov--Drell--Hearn sum rule and related integrals

TL;DR

This study uses partial-wave analysis of single-pion photoproduction to evaluate its contribution to key sum rules, confirming convergence and saturation levels vary across different sum rules and nucleons.

Contribution

It provides a detailed phenomenological evaluation of single-pion contributions to multiple sum rules using partial-wave analysis data.

Findings

Single-pion contribution converges before 2 GeV in photon energy.

Almost saturates the GDH sum rule for the proton.

Large fraction of the neutron GDH sum rule remains unsaturated.

Abstract

Phenomenological amplitudes obtained in partial-wave analyses (PWA) of single-pion photoproduction are used to evaluate the contribution of this process to the Gerasimov-Drell-Hearn (GDH), Baldin and Gell-Mann-Goldberger-Thirring (GGT) sum rules, by integrating up to 2 GeV in photon energy. Our study confirms that the single-pion contribution to all these sum rules converges even before the highest considered photon energy, but the levels of saturation are very different in the three cases. Single-pion production almost saturates the GDH sum rule for the proton, while a large fraction is missing in the neutron case. The Baldin integrals for the proton and the neutron are both saturated to about four fifths of the predicted total strength. For the GGT sum rule, the wide variability in predictions precludes any definitive statement.