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

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.

Comments: Talk at the MENU2007 Conference