Indirect Determination of the GDH Integrand on the Deuteron near Photodisintegration Threshold

Data obtained from measurements\footnote{B. Sawatzky, Ph.D. thesis, Univ. of Virginia, 2005.} recently performed at the High Intensity $\vec{\gamma}$-ray Source (HI$\vec{\gamma}$S) are being analyzed to extract the Gerasimov-Drell-Hearn (GDH) integrand on the deuteron at $\gamma$-ray energies of 3.5, 4.0, 6.0, and 10.0 MeV. Linearly polarized $\gamma$-rays were used to extract the shape of the polarized differential cross section for the $d(\vec{\gamma},n)p$ reaction near breakup threshold using the 88 neutron detectors of the BLOWFISH array. The coefficients of a Legendre polynomial expansion of the data were extracted and written in terms of the amplitudes and phases of the transition matrix elements. A grid search was performed to determine the amplitudes of the T-matrix elements, using the phase shifts obtained from $n$-$p$ scattering data\footnote{SAID Analysis, http://gwdac.phys.gwu.edu/.} to fix the relative phases. The amplitudes are used in a low-energy expansion of the GDH integrand to determine the integrand values at each energy. This talk will provide a brief overview of the experiment, describe how the amplitudes were extracted, and compare the results obtained for the GDH integrand to theory\footnote{H. Arenh\"ovel {\it et al.} Nucl. Phys., {\bf A631}(1998) 612c.}.