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

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 ($\ddot{I}‡$PT). The data cover the resonance region, up to an invariant mass of $W\approx 1.9$~GeV. The generalized Gerasimov-Drell-Hearn sum, the moment $\bar{\hat{I}}{“}_1^d$ and the integral $\bar{I}_γ^d$ related to the spin polarizability $γ_{0}^{d}$ 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 $\ddot{I}‡$PT calculations and models. These results are the first in a program of benchmark measurements of polarization observables in the $\ddot{I}‡$PT domain.

Version 1: version published in Phys. Rev. Lett. 6 pages, 3 figures. Supplementary material: data table for g1d and its moments (10 pages) V2: Figures labels changed and text slightly modified to clarify the exact nature of the measured moments V3: Corrected a typo page 5 for the theoretical value expected for deuteron GDH sum rule (agreement between measurement and expectation is improved)