Measurement of Helicity-Dependent Photoabsorption Cross Sections on the Neutron from 815 to 1825 MeV

Helicity-dependent total photoabsorption cross sections on the deuteron have been measured for the first time at ELSA (Bonn) in the photon energy range from 815 to 1825 MeV. Circularly polarized tagged photons impinging on a longitudinally polarized LiD target have been used together with a highly efficient $4\pi$ detector system. The data around 1 GeV are not compatible with predictions from existing multipole analyses. From the measured energy range an experimental contribution to the GDH integral on the neutron of [$33.9\pm 5.5(\mathrm{stat})\pm 4.5(\mathrm{syst})$] $\mu \mathrm{b}$ is extracted.

Figure 1

Predictions for $\Delta {\sigma }^n$ (solid lines) and $\Delta {\sigma }^p$ (dashed lines) as functions of the photon energy $\nu$. Resonance region: one pion contribution from the 2003 solution [6] of MAID [7, 8]. High energy behavior (inset) from a Regge approach [9].

Figure 2

$\Delta {\sigma }^n(\nu )$ in comparison with $\Delta {\sigma }^p(\nu )$ [5], theoretical predictions from MAID [6, 7, 8] in the resonance region (solid and dashed lines) and a Regge approach for higher energies [9] (dash-dotted line). Error bars are statistical only.