First measurements of spin-dependent double-differential cross sections and the Gerasimov-Drell-Hearn integrand from $^{3}\vec{He}\left ( \vec{\gamma }, n \right )pp$ at incident photon energies of 12.8 and 14.7 MeV

The first measurement of the three-body photodisintegration of longitudinally polarized $^{3}He$ with a circularly polarized $\gamma$-ray beam was carried out at the High Intensity $\gamma$-ray Source facility located at Triangle Universities Nuclear Laboratory. The spin-dependent double-differential cross sections and the contributions from the three-body photodisintegration to the $^{3}He$ Gerasimov-Drell-Hearn integrand are presented and compared with state-of-the-art three-body calculations at the incident photon energies of 12.8 and 14.7 MeV. The data reveal the importance of including the Coulomb interaction between protons in three-body calculations.