Investigation of Nuclear Structure with Intermediate Energy Photons

Catholic University Of America, Washington DC

Investigators

Abstract

The Catholic University of America (CUA) group will study the structure of nucleons and the role of quarks in determining this structure, principally using instrumentation in Hall B at The Thomas Jefferson National Accelerator Facility (JLab). An essential tool In this work is the photon tagger -- a device which measures the Incident energy of a photon that subsequently produces a reaction of interest in a nuclear target. The reaction products are then collected and analyzed, typically by the CEBAF Large Acceptance Spectrometer (CLAS), in order to extract fundamental information of interest about the nuclear interactions involved. The CUA group had major responsibility for the design, construction and commissioning of the tagger, which has subequently been used by about 40% of the experiments in Hall B. In addition to ongoing commitments to Hall B, we have begun work on a tagger design for the new Hall D -- a component of the proposed upgrade of JLab to higher energy. As founding members of the CLAS Collaboration, the CUA group will continue to participate in data-taking and analysis activity for most experiments that use the tagger. A study of special interest to us is the photoproduction of K mesons and hyperons in order to improve understanding of the role of strange quarks in the nucleon. Current investigations include production of neutral K mesons, the dissertation project for a CUA doctoral student. We are refining a proposal to study contributions to the Gerasimov-Drell-Hearn sum rule, a quantity related to the most fundamenetal properties of the proton. Apart from the CLAS collaboration, we are partners in two other projects which use the tagger but not the CLAS detector - a measurement of rare decays of the phi meson, and a forthcoming measurement of the lifetime of the neutral pion using the Primakoff effect.