Speaker
Description
The nucleon spin structure is an important aspect of hadronic physics, and spin sum rules have been extensively used to study it. We will report on the latest experimental results published on nucleon spin sum rules. The data were taken at Jefferson Lab in Hall A and B by experiments E97-110 and EG4, respectively. They covered the very low $Q^2$ domain, down to $Q^2 \sim 0.02$ GeV$^2$, Chiral Effective Field Theory ($\chi$EFT) is applicable, thereby providing a test of its predictions. While some of the measurements agree with the state-of-the-art $\chi$EFT theoretical predictions, others are in tensions, including $\delta_{LT}^n(Q^2)$ for which $\chi$EFT prediction was expected to be robust. This suggests that $\chi$EFT does not yet consistently describe nucleon spin observables, even in the very low $Q^2$ domain covered by the experiments.
