Hadron Spectroscopy using Polarized Photons

Catholic University Of America, Washington DC

Investigators

Abstract

The scattering of high energy photons on protons has been studied for many decades. The long interest in this endeavor is largely motivated by the study of nucleon and meson excitations, which manifest themselves as specific configurations of quarks inside the nucleon. With the development of high energy, highly-polarized photon beams and ultra-cold polarized targets, which keep the orientation of the nucleon spin frozen at a few milliKelvin, we finally are able to measure all components of the scattering amplitudes in the form of polarization observables, and thus to disentangle unambiguously the resonant contributions to the scattering. CUA is a leading institution in this program that is being conducted in Hall B at the Thomas Jefferson National Accelerator Facility (JLab) in Newport News, VA. Two CUA graduate students are extracting all polarization observables for the interaction of photons and protons in which so-called strange particles are produced, particles that do not occur in nature but only in high-energy scattering. Their research builds the corner stone of the program. The excitation of the glue that holds quarks and antiquarks closely together in mesons is predicted by the theory of strong interaction but has not experimentally been established. The GlueX experiment being constructed at JLab will be devoted to the search for such excitations. By using a high energy, highly polarized photon beam and a high-resolution detector with complete coverage, the GlueX experiment is expected to settle the question. CUA's contribution to the experiment is the construction and maintenance of the broad-band tagging hodoscope and the polarized photon source. The construction project provides excellent research opportunities for CUA's undergraduate students in physics and engineering who will be guided to take over key roles in prototyping, constructing and testing the hodoscope. The grant provided by NSF will support CUA's efforts in the frozen-spin target program in JLab's Hall B as well as the GlueX construction project.