First measurement of polarized spin-density matrix elements and differential cross sections d$\sigma$/d$t$ in $\omega$~photoproduction off the proton for $2.7<E_{\gamma }<5.2$ GeV using CLAS at Jefferson Lab

Abstract

We report on the differential cross sections d$\sigma$/d$t$, the unpolarized spin-density matrix elements ${\rho }_{00}^0$, ${\rho }_{1-1}^0$, Re\,${\rho }_{10}^0$, and the first extraction of the polarized elements Im\,${\rho }_{10}^3$, Im\,${\rho }_{1-1}^3$ for the reaction $\gamma p\to p\omega$ using the CLAS spectrometer at Jefferson Laboratory. The $\omega$~mesons were detected in their dominant charged decay mode, $\omega \to {\pi }^{+}{\pi }^{-}{\pi }^0$, and all $t$-dependent results are presented in a fine binning for incident photon energies between 2.73 and 5.16~GeV (corresponding to the center-of-mass energy range $W\in [2.45,3.25]$~GeV). All matrix elements are first measurements for $-t>0.6$~GeV${}^2$. Moreover, differential cross sections d$\sigma$/d(cos\,${\Theta }_{c.m.}^{\omega }$) and the corresponding angle-dependent unpolarized spin-density matrix elements in the Adair frame are presented for the incident photon energy range 1.56--3.80~GeV (corresponding to $W\in [1.95,2.83]$~GeV). These new $\omega$~photoproduction data are consistent with earlier CLAS results but extend the energy range well beyond the nucleon resonance region into the Regge regime. The comparison with Regge-theory-based model predictions shows that the new data impose more stringent constraints on our understanding of $\omega$~photoproduction.

9 pages, 4 figures, accepted for publication by Physics Letters B