First measurement of polarized spin-density matrix elements and differential cross sections d$σ$/d$t$ in $ω$~photoproduction off the proton for $2.7 < E_γ< 5.2$ GeV using CLAS at Jefferson Lab

Abstract

We report on the differential cross sections d$σ$/d$t$, the unpolarized spin-density matrix elements $ρ^0_{00}$, $ρ^0_{1-1}$, Re\,$ρ^0_{10}$, and the first extraction of the polarized elements Im\,$ρ^3_{10}$, Im\,$ρ^3_{1-1}$ for the reaction $γp\to pω$ using the CLAS spectrometer at Jefferson Laboratory. The $ω$~mesons were detected in their dominant charged decay mode, $ω\to π^+π^-π^0$, 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$σ$/d(cos\,$Θ_{\rm \,c.m.}^{\,ω}$) 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 $ω$~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 $ω$~photoproduction.