Book Description

Meson photoproduction off the nucleon has long been serving as a tool for understanding the properties of hadrons. At lower energy scales, the production mechanisms are dominated by the $s$-channel inelastic scattering process, where the proton absorbs the photon, gets excited to the resonance state, and then decays. Nucleon resonances have been extensively studied in this energy regime using techniques such as partial wave analysis. When the energy scale increases, the production mechanism gradually transitions from the formation of nucleon resonances to the pure scattering process, corresponding to the $t$- and $u$-channel exchange. However, the scarcity of cross section and polarization data over the photon energy range 3-6 GeV have thus far hindered our understanding of the mechanism transition from nucleon resonance to the $t$-channel Pomeron and Reggeon exchange. This work presents differential cross sections for the reaction $\\\\gamma p\\\\rightarrow p\\\\eta$ with energy-tagged photon energies between 1.2 and 4.7 GeV using the CLAS spectrometer at Jefferson Laboratory. The $\\\\eta$ meson is reconstructed in its dominant charged decay channel $\\\\eta\\\\rightarrow \\\\pi^{+}\\\\pi^{-}\\\\pi^{0}$. The energy scale extends from the nucleon resonance regime to the Regge regime, allowing for studying the $t$-channel exchange mechanisms. The d$\\\\sigma/$d$\\\\Omega$ differential cross sections are compared with predictions of $\\\\eta$-MAID 2018 and the latest solution of the Bonn-Gatchina coupled-channel analysis. In the energy regime $W>2.5$ GeV, the d$\\\\sigma/$d$t$ differential cross sections are presented in comparison with the Regge model from the Joint Physics Analysis Center. The data confirm the expected dominance of $\\\\rho$, $\\\\omega$ vector-meson exchange. Differential cross sections and spin density matrix elements (SDMEs) are also measured for the reaction $\\\\gamma p\\\\rightarrow p\\\\omega$ in the energy range $1.6E_{\\\\gamma}