Abstract
Investigations of in-medium properties of the {\eta}'-meson are presented. The photoproduction of {\eta}'-mesons off C, Ca, Nb and 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 {\eta}'-meson to be of the order of 20 MeV. The measured width is sufficently narrow to encourage a search for {\eta}' mesic states. Recent results on the momentum distribution of the transparency ratio and in-medium width of the {\eta}'-meson are presented and discussed.
Highlights
The origin of hadron masses is one of the open questions of QCD in the low-energy sector
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
There have been many theoretical studies discussing the idea that the chiral symmetry may be at least partially restored in a nuclear medium [1,2,3] which might have an impact on the in-medium η′ mass
Summary
The origin of hadron masses is one of the open questions of QCD in the low-energy sector. A refined analysis of this reaction, comparing the cross section with that of the pp → ppπ0 reaction, concluded that the η′ scattering length should be of the order of magnitude of that of the πN interaction and |aη′N| ∼ 0.1 fm [6] This indicates a rather weak η′N interaction. Knowledge of the η′ in-medium width is important for the feasibility of observing η′ - nucleus bound systems theoretically predicted in some models [8].
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