Polarization asymmetry in the photodisintegration of the deuteron

The reaction ${}_{}{}^2{}_{}{}^{}(\gamma$,p)n has been studied using a monochromatic and polarized gamma ray beam at energies $E_{\gamma }$=19.8, 29.0, 38.6, and 60.8 MeV. The beam of an intensity ∼4×${10}^5$ γ/sec was obtained by Compton back scattering of mode-locked laser light off electron bunches in the Adone storage ring. Photoneutron yields were measured at nine neutron angles ${\mathrm{theta}}_{\mathrm{n}\mathrm{\simeq }}$15, 30, 45, 60, 90, 120, 135, 150, and 165 deg in the center of mass (c.m.) for $E_{\gamma }$=19.8, 29.0, and 38.6 MeV, and at ${\mathrm{theta}}_{\mathrm{n}\mathrm{\simeq }}$30, 60, 90, 120, and 150 deg c.m. for $E_{\gamma }$=60.8 MeV. The polarization independent component $I_0$(theta) of the differential cross section and the polarization dependent component ${\mathrm{PI}}_1$(theta) were deduced and the angular distribution of the azimuthal asymmetry factor Σ(theta)=$I_1$(theta)/$I_0$(theta) was obtained. An extensive comparison with theory has been carried out and the inclusion of corrections due to meson exchange currents and to Δ-isobar configurations have been shown to be mandatory at energies $E_{\gamma }$≳40 MeV. Theoretical and experimental implications of intermediate energy deuteron photo- disintegration studies are discussed in some detail.