Photoproduction of the $\omega$ Meson on the Proton at Large Momentum Transfer

The differential cross section, $d\sigma /dt$, for $\omega$ meson exclusive photoproduction on the proton above the resonance region ($2.6<W<2.9\mathrm{G}\mathrm{e}\mathrm{V}$) was measured up to a momentum transfer $-t=5{\mathrm{G}\mathrm{e}\mathrm{V}}^2$ using the CLAS detector at Jefferson Laboratory. The $\omega$ channel was identified by detecting a proton and ${\pi }^{+}$ in the final state and using the missing mass technique. While the low momentum transfer region shows the typical diffractive pattern expected from Pomeron and Reggeon exchange, at large $-t$ the differential cross section has a flat behavior. This feature can be explained by introducing quark interchange processes in addition to the QCD-inspired two-gluon exchange.

Figure 1

The Feynman diagrams corresponding to (a) two-gluon exchange from a single quark, (b) two-gluon exchange taking into account quark correlations in the nucleon, and (c) quark exchange.

Figure 2

Missing mass squared for the reaction $\gamma p\to p{\pi }^{+}X$ with $E_{\gamma }$ between 3.19 and 3.91 GeV. The hatched area corresponds to the $\omega$ candidates.

Figure 3

Missing mass for $\gamma p\to p+X$ around the $\omega$ mass with $E_{\gamma }$ between 3.74 and 3.92 GeV. The spectra are fitted to a Gaussian $+4\mathrm{t}\mathrm{h}$-order polynomial.

Figure 4

Differential cross section for $\gamma p\to p\omega$ as measured in CLAS for the energy bin $E_{\gamma }=3.38–3.56\mathrm{G}\mathrm{e}\mathrm{V}$ compared with existing data. See the text for the explanation of the curves. In this energy bin, ${\theta }_{\omega }^{*}=90°$ corresponds to $-t=2.52{\mathrm{G}\mathrm{e}\mathrm{V}}^2$.

Figure 5

Differential cross section measured in CLAS. The fourth energy bin ($E_{\gamma }=3.38–-3.56\mathrm{G}\mathrm{e}\mathrm{V}$) is shown in Fig. 4.