Abstract for the DNP fall meeting (Asilomar CA)

Electro- and photoproduction of omega at CLAS


The electro- and photoproduction data taken in 1998 and 1999
with CLAS were analyzed with respect to the $\omega p$ channel.
Quark model calculations indicate that some of the baryon resonances
that have not yet been observed are expected to couple strongly to $\gamma N$
as well as $\omega N$.
The vector meson is identified in the decay mode $\omega\to\pi^+\pi^-\pi^0$. 
The electroproduction data set was selected by measurement of the
scattered electron in coincidence with the recoil proton and the $\pi^+$
from the $\omega$ decay. Missing mass technique was applied to reduce the
$\rho^0$ background. The $\omega$ signal was extracted via background
subtraction in the $MM_{ep}$ missing mass distribution.

For photoproduction the recoil proton in coincidence with 
two charged pions were measured and the missing $\pi^0$ identified
via missing mass technique. The three pion mass spectrum shows
a strong $\omega$ signal that is enhanced in forward direction
as expected from diffractive and pion-exchange processes.
However,  the (preliminary) differential cross section for $W<2$ GeV
is not consistent with t-channel processes. The enhancement at 
$\cos\theta^*\simeq 90^\circ$ indicates s-channel contributions
that is confirmed by the angular distribution of the decay pions.