Gant South Building

Differential cross sections for forward-angle photoproduction of π⁰, η, and η′ pseudoscalar mesons were measured using data from the RadPhi experiment conducted in Hall B at Jefferson Lab. RadPhi utilized a tagged bremsstrahlung photon beam incident on a stationary ⁹Be target, with a detector system configured to trigger on a recoil proton in coincidence with multiple neutral showers in the calorimeter. Events were reconstructed through kinematic fitting, with background suppressed via sideband subtraction and Monte Carlo modeling of nucleon resonance contributions. Cross sections were extracted over the photon energy range 4.4 - 5.4 GeV and binned in momentum transfer |t|, providing measurements from one of the first high-statistics experiments of forward η and η??? production from a nuclear target at these energies. Acceptance corrections were applied using a detailed GEANT-based simulation of the detector geometry and response. The resulting cross sections are consistent with 2020 CLAS results when scaled by the number of protons in beryllium, and show broad agreement with other data and theoretical models. In parallel, a high-resolution photon tagger detector, the Tagger Microscope (TAGM), was designed, constructed, and commissioned for the GlueX experiment in Hall D at Jefferson Lab. The TAGM was developed to improve energy resolution near the coherent bremsstrahlung peak by detecting post-bremsstrahlung electrons across a one GeV range along the focal plane of the tagging spectrometer. The detector consists of a 5x102 array of 2x2 mm² square BCF-20 plastic scintillating fibers thermally fused to BCF-98 light guide fibers optically coupled to silicon photomultipliers. These fibers are mounted in a precision-machined framework enabling fine positional adjustments to maintain precise alignment with post-bremsstrahlung electron trajectories, while ensuring mechanical rigidity, thermal stability, optical isolation, minimal inactive area, and radiation shielding for electronics. The construction effort involved extensive testing of fiber quality, light transmission, thermal fusing, radiation hardness, and defect analysis using SEM and EDX techniques. Following its installation and commissioning, the TAGM became a critical component of the GlueX beamline, enabling high-precision tagging essential for studies of hybrid mesons and gluonic excitations.