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

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 $W\approx 1.9$~GeV. The generalized Gerasimov-Drell-Hearn sum, the moment ${\bar{\mathrm{\Gamma }}}_1^d$ 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.