Measurements of HD (gamma, pi) and Implications for the Convergence of the Gerasimov-Drell-Hern Integral

We report new measurements of inclusive {pi} production from frozen-spin HD for polarized photon beams covering the {Delta}(1232) resonance. These provide data simultaneously on both H and D with nearly complete angular distributions of the spin-difference cross sections entering the Gerasimov-Drell-Hearn (GDH) sum rule. Recent results from Mainz and Bonn exceed the GDH prediction for the proton by 22 {mu}b, suggesting as yet unmeasured high-energy components. Our {pi}{sup 0} data reveal a different angular dependence than assumed in Mainz analyses and integrate to a value that is 18 {mu}b lower, suggesting a more rapid convergence. Our results for deuterium are somewhat lower than published data, considerably more precise, and generally lower than available calculations.