Experimental studies at low $Q^2$ of the spin structure of the nucleon at Jefferson Lab

TL;DR

This paper summarizes Jefferson Lab's experimental efforts to map the nucleon spin structure functions at low Q^2, providing benchmarks for theoretical models and highlighting ongoing challenges for Chiral Effective Field Theory.

Contribution

It presents comprehensive low Q^2 measurements of nucleon spin structure functions, extending previous high Q^2 studies and offering critical data for testing Chiral Effective Field Theory.

Findings

Data challenge current $FT$ predictions

Benchmark measurements for $FT$

Progress in understanding nucleon spin structure

Abstract

We summarize the experimental program of Jefferson Lab that studies the nucleon spin structure at low $Q^2$. This program completes the precise experimental mapping of the nucleon spin structure functions $g_1(\nu, Q^2)$ and $g_2(\nu, Q^2)$ and their moments started at SLAC, CERN and DESY at high $Q^2$, and continued at Jefferson Lab at intermediate $Q^2$. The results presented cover the domain where Chiral Effective Field Theory ($\chi$EFT) should describe the strong interaction. They provide a comprehensive set of benchmark measurements for $\chi$EFT. The preliminary conclusion is that nucleon spin structure data are still challenging for $\chi$EFT in spite of the notable improvements in these calculations.