First measurement of the asymmetry and the Gerasimov-Drell-Hearn integrand from the He 3 ⃗ ( γ ⃗ , p ) H 2 reaction at an incident photon energy of 29 MeV

The first measurement of the $\\stackrel{P\\vec}{^{3}\\mathrm{He}}(\\stackrel{P\\vec}{\\ensuremath{\\gamma}},p)^{2}\\mathrm{H}$ process was performed at the High Intensity $\\ensuremath{\\gamma}$-ray Source ($\\mathrm{HI}\\ensuremath{\\gamma}\\mathrm{S}$) facility at Triangle Universities Nuclear Laboratory using a circularly polarized, monoenergetic $\\ensuremath{\\gamma}$-ray beam and a longitudinally polarized $^{3}\\mathrm{He}$ target. The spin-dependent asymmetry and the contribution from the two-body photodisintegration to the $^{3}\\mathrm{He}$ Gerasimov-Drell-Hearn integrand are extracted and compared with state-of-the-art three-nucleon system calculations at the incident photon energy of 29 MeV. The data are in general agreement with the various theoretical predictions based on the Siegert theorem or on explicit inclusion of meson-exchange currents.