Near-threshold Deuteron Photodisintegration: an Indirect Determination of the Gerasimov-Drell-Hearn Sum Rule and Forward Spin Polarizability (γ0) for the Deuteron at Low Energies

It is shown that a measurement of the analyzing power obtained with linearly polarized \ensuremath{\gamma}-rays and an unpolarized target can provide an indirect determination of two physical quantities. These are the Gerasimov-Drell-Hearn (GDH) sum rule integrand for the deuteron and the sum rule integrand for the forward spin polarizability (${\ensuremath{\gamma}}_{0}$) near photodisintegration threshold. An analysis of data for the $d(\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}},n)p$ reaction and other experiments is presented. A fit to the world data analyzed in this manner gives a GDH integral value of $\ensuremath{-}603\ifmmode\pm\else\textpm\fi{}43\ensuremath{\mu}$b between the photodisintegration threshold and 6 MeV. This result is the first confirmation of the large contribution of the ${}^{1}{S}_{0}(M1)$ transition predicted for the deuteron near photodisintegration threshold. In addition, a sum rule value of 3.75\ifmmode\pm\else\textpm\fi{}0.18 fm${}^{4}$ for ${\ensuremath{\gamma}}_{0}$ is obtained between photodisintegration threshold and 6 MeV. This is a first indirect confirmation of the leading-order effective field theory prediction for the forward spin-polarizability of the deuteron.