The photoproduction of ω mesons on nuclei has been investigated using the Crystal Barrel/TAPS experiment at the ELSA tagged photon facility in Bonn. The aim is to study possible in-medium modifications of the ω meson via the reaction γ+A→ω+X→π⁰γ+X^'. Results obtained for Nb are compared to a reference measurement on a LH₂ target. While for recoiling, long-lived mesons (π⁰, η, and η^'), which decay outside of the nucleus, a difference in the line shape for the two data samples is not observed, we find a significant enhancement towards lower masses for ω mesons produced on the Nb target. For momenta less than 500 MeV/c an in-medium ω meson mass of Mmedium=[722_-4⁺⁴(stat)_-5⁺³⁵(syst)] MeV/c² has been deduced at an estimated average nuclear density of 0.6ρ₀.
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Trnka et al. (2005) studied this question.
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