Helicity Dependence and Contribution to the Spin Asymmetry and the GDH Sum Rule of the \(\vec{\gamma }\vec{d} \to \pi ^{0}d\) Reaction Near the η-Threshold

Abstract

The helicity dependence of the \(\vec{\gamma }\vec{d} \to \pi ^{0}d\) reaction is studied for incident photon lab-energies near the η-threshold at backward center-of-mass pion angles. The influence of first-order rescattering with intermediate production of both π- and η-mesons on the doubly polarized differential and total cross sections for parallel and antiparallel helicity states is investigated. Then the contribution of \(\vec{\gamma }\vec{d} \to \pi ^{0}d\) to the deuteron spin asymmetry of the total cross section is calculated and its contribution to the Gerasimov–Drell–Hearn (GDH) integral for the deuteron is explicitly evaluated by integration up to a photon lab-energy of 900 MeV. Moreover, the double polarization E-asymmetry is predicted. Although the first-order rescattering effect is found to be negligible in the doubly polarized total photo-absorption cross sections and the deuteron GDH integral, it reached on average about 40% in the doubly polarized differential cross sections and the helic...