Measurement of the Q^2 Dependence of the Deuteron Spin Structure Function g_1 and its Moments at Low Q^2 with CLAS

TL;DR

This study measures the deuteron spin structure function g_1 at low Q^2, providing precise data that tests chiral perturbation theory predictions and benchmarks polarization observables in this regime.

Contribution

First precise measurements of deuteron spin structure functions and related moments at very low Q^2, extending the experimental data into the chiral perturbation theory domain.

Findings

Data cover resonance region up to W≈1.9 GeV

Precise determination of generalized GDH sum and spin polarizability at low Q^2

Comparison with chiral perturbation theory models

Abstract

We measured the $g_1$ spin structure function of the deuteron at low $Q^{2}$, where QCD can be approximated with chiral perturbation theory ($\chi$PT). The data cover the resonance region, up to an invariant mass of $W\approx1.9$~GeV. The generalized Gerasimov-Drell-Hearn sum, the moment $\bar{\Gamma}_{1}^{d}$ and the integral $\bar{I}_\gamma^d$ related to the spin polarizability $\gamma_{0}^{d}$ are precisely determined down to a minimum $Q^2$ of 0.02~GeV$^2$ for the first time, about 2.5 times lower than that of previous data. We compare them to several $\chi$PT calculations and models. These results are the first in a program of benchmark measurements of polarization observables in the $\chi$PT domain.