Recent Results from the Joint Physics Analysis Center (JPAC)

The Joint Physics Analysis Center (JPAC) was formed in 2013 originally to provide theoretical support for the ongoing hadron spectroscopy program at Jefferson Laboratory. Since then, it has grown into an international collaboration focused on hadron spectroscopy. An ongoing focus of the JPAC Collaboration is understanding the particle content produced by the interactions of hadrons. The last 20 years have seen a renewed interest in hadron spectroscopy with the discovery of hadrons which cannot be explained by the standard quark model. Such exotic hadrons have posed new challenges for both their experimental measurement and their theoretical interpretation. Photoproduction machines like GlueX are natural places to look for such exotic hadrons. In this talk, I will discuss the recent progress made by JPAC in understanding photoproduction reactions relevant for the ongoing GlueX experiment. In particular, I'll discuss theoretical studies of two-meson photoproduction including a description of the angular moments of two charged pion photoproduction, a description of the pion-Delta baryon spin-density matrix elements and the description of neutral double pion photoproduction in the double-Regge region. Finally, I'll discuss formal developments in Regge theory applicable for photoproduction, and describe the application of finite-energy sum rules to provide constraints on the low-energy partial waves from the high-energy data.