Photoproduction of mesons from nuclei —in-medium properties of hadrons

Abstract

Recent experimental results on the in-medium properties of hadrons obtained with photoproduction of mesons from nuclei are discussed. The experiments were done with the TAPS detector at the tagged photon beam of the MAMI accelerator in Mainz. Measured were the final states π o X , η X , 2 π o X , and π o π ± X for 12C, 40Ca, 93Nb, and 208Pb up to the second resonance region. The results were used for an investigation of the in-medium properties of the P 33(1232), the P 11(1440), the D 13(1520) and the S 11(1535) resonances. It was found that the cross sections can be spilt into a component which originates from the low density surface region of the nuclei and a component which scales like the nuclear volume. The energy dependence of the surface component is strikingly similar to that of the deuteron; it shows a clear signal for the second resonance peak. The volume component is lacking this peak and shows an enhancement at intermediate energies. Furthermore, the measurement of coherent η photoproduction and the final state p π o from 3He is discussed in the context of the search for η mesic nuclei.