Photoproduction of $\omega$ and $\omega$ in the Nuclear Medium

TL;DR

This paper reanalyzes ELSA data on omega meson production in nuclei, concluding that the medium primarily causes a large width increase rather than a mass shift, and discusses the implications for observing omega bound states.

Contribution

The study provides a new interpretation of omega meson in-medium modifications, emphasizing width effects over mass shifts and clarifying background influences in experimental signals.

Findings

Omega width in medium is large, with no significant mass shift.

Omega bound states are unlikely to be observed with current resolution.

Background effects can produce a two-peak structure mimicking bound states.

Abstract

We reanalyze data from ELSA on $\omega$ production in nuclei, from where claims of a large shift of the mass were made earlier, which are tied to a certain election of the background in nuclei, very different in shape to the one on the proton. The reanalysis shows that the data demand a very large width of the $\omega$ in the medium, with no need for a shift of the mass, for which the experiment is quite insensitive. We study possible $\omega$ bound states in the nucleus and find that, even assuming a small width, they could not be observed with the present ELSA resolution. Finally we show that, due to the interplay of background and $\omega$ signal, a two bump structure appears with the ELSA set up for the $(\gamma,p)$ reaction that should not be misidentified with a signal of a possible $\omega$ bound state in the nucleus.