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The GlueX Experiment in Hall D at Jefferson Lab ultimately aims to provide evidence of hybrid mesons, qq̄ pairs with gluonic excitations, which are predicted by quantum chromodynamics calculations on the lattice. GlueX features a linearlypolarized photon beam incident on a liquid hydrogen target and a nearly-4π hermetic detector capable of measuring positions and momenta of both charged and neutral final state particles generated in the target. The short-term physics goals of GlueX are to measure observables and properties of the known particles, especially those that are likely decay products of hybrids, such as the η and η′ mesons. An overview of the detector subsystems and the long-term physics goals of GlueX are presented, along with analyses on the Σ beam asymmetry of the η and η′ mesons. The measurements of Σ are presented versus the four-momentum transfer squared using a photon beam energy of 8.2–8.8 GeV in the three main decay channels of the η (η → 2γ, η → π+π−π0, and η → 3π) and the largest branching fraction decay channel of the η′ (η′ → π+π−η, with η → 2γ). These are the first results for the beam asymmetry of the η′ measured at this beam energy. The results, which are in agreement with past published measurements for the η by GlueX and with modern theory predictions for the η and η′, indicate a dominance of natural parity exchange in the resonance production mechanism.

Measurement of the Beam Asymmetry for the ETA and ETA Prime Mesons with the GlueX Experiment