Two-nucleon photon absorption onHe3in theΔ(1232) region

Abstract

Cross sections were determined in the Δ(1232) excitation region for the reactions ${}_{}{}^3{}_{}{}^{}\mathrm{H}$(γ,p)pn and ${}_{}{}^2{}_{}{}^{}\mathrm{H}$(γ,p)n at several photon energies and proton emission angles. Inclusive proton spectra were measured with a magnetic spectrometer, using quasimonochromatic $e^{+}$-annihilation photons. The ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ data can be mainly accounted for by predictions assuming photon absorption by a pair of nucleons, except in the high-momentum part of the proton spectra. They clearly indicate the need for additional contributions, such as three-body absorption mechanisms.