Quasi-free $\pi^0$ photoproduction from the bound nucleon

Abstract

Differential cross-sections for quasi-free $\pi^0$ photoproduction from the proton and neutron bound in the deuteron have been measured for $E_\gamma = 200\mbox{--}400$ MeV at $\theta_\gamma^{\rm lab} = 136.2^\circ$ using the Glasgow photon tagger at MAMI, the Mainz 48 cm $\clubsuit\times 64$ cm NaI(Tl) photon detector and the Göttingen SENECA recoil detector. For the proton measurements made with both liquid-deuterium and liquid-hydrogen targets allow direct comparison of “free” $\pi^0$ photoproduction cross-sections as extracted from the bound-proton data with experimental free cross-sections which are found to be in reasonable agreement below 320 MeV. At higher energies the “free” cross-sections extracted from quasi-free data are significantly smaller than the experimental free cross-sections and theoretical predictions based on multipole analysis. For the first time, “free” neutron cross-section have been extracted in the $\Delta$ -region. They are also in agreement with the predictions from multipole analysis up to 320 MeV and significantly smaller at higher photon energies.