In-medium Properties of theη′-Meson from Photonuclear Reactions

Abstract

Abstract. Investigations of in-medium properties of the η ′ -meson are presented. The photoproduction of η ′ -mesons off 12 C, 40 Ca, 93 Nb and 208 Pb nuclei has been measured with the Crystal Barrel/TAPS detector system at the ELSA accelerator in Bonn. Comparing the meson yield per nucleon within a nucleus to the yield on a free nucleon, information on the absorption of the meson through inelastic channels in the nuclear medium and the related in-medium width of the meson is provided. From this so called transparency ratio we found the in-medium width of the η ′ -meson to be of the order of 20 MeV. The measured width is sufficently narrow to encourage a search for η ′ mesic states. Recent results on the momentum distribution of the transparency ratio and in-medium width of the η ′ -meson are presented and discussed.