Measurement of the ReactionHe4(γ,π0)He4forEγ=290MeV

We report measurements of differential cross sections for the reaction ${}_{}{}^4{}_{}{}^{}\mathrm{He}(\gamma ,{\pi }^0){}_{}{}^4{}_{}{}^{}\mathrm{He}$ with a photon energy of 290 MeV. Use of a good-resolution ${\pi }^0$ spectrometer allowed restriction of events to those where the residual ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ nucleus was left in the ground state (the coherent process). By detecting the ${\pi }^0$ directly, we thus provide the first forward-angle data for this reaction in the $\Delta$-resonance region. Our results are in good agreement with a recent $\Delta$-hole model calculation.