Nucleon Structure and Nuclear Force Studies

Kent State University, Kent OH

Investigators

Abstract

This award is to support the research activities of two professors, their graduate students and a Senior Research Associate at Kent State University in the area of experimental medium-energy nuclear physics. The general objectives are the study of the structure of the nucleon (neutron or proton) and the nature of the nuclear force. This group is involved in experiments being performed, or to be performed at the Jefferson National Accelerator Facility (Jlab) in Virginia and at the Relativistic Heavy-Ion Collider (RHIC) on Long Island, New York. An experiment is in progress at Jlab to determine the charge distribution inside the neutron. The neutron, while neutral overall, is known to consist of objects with both positive and negative charges. These objects are called "quarks". The quarks are held together by the exchange of particles called "gluons". Exactly how the quarks combine, move, and interact inside the neutron is not known. A precise measurement of the charge distribution, called the Electric Form Factor, will provide one of the most sensitive tests available of various models of the neutron structure. These measurements are only recently possible and require the electron beam characteristics now available at Jlab and involve the use of a large-volume neutron polarimeter developed by this group in experiments performed during the last decade at other accelerator facilities. The development, installation, calibration, and operation of the polarimeter represents the unique contribution of this group to this important experiment. This group plans also to perform another experiment at Jlab to study short-range correlation between nucleons inside nuclei. Such short-range correlations are known to exist, but the exact nature and strength of such correlations are only poorly determined. This group will bring its expertise with neutron detectors to help study such correlations involving neutrons. This group has recently joined an effort planned to study interactions between colliding beams of polarized protons using the "STAR" detector at RHIC (STAR stands for Solenoidal Tracker at RHIC). The object of this study is to determine the exact origin of the intrinsic angular momentum, or spin, of the proton. The spin, like the charge distribution, arises from the existence, interactions and movements of the constituents of the proton, generally believed to be the quarks and gluons. To date, only the contributions from the quarks has been determined; this project offers the possibility of determining the contribution to the spin of the proton due to gluons. In order to measure these contributions, it is necessary to observe hadronic jets produced at relatively small angles in the collisions. This group, together with a collaboration of other researchers from Indiana University, Argonne National Laboratory, and others, will construct a new "end-cap calorimeter" to be installed at one end of the present STAR detector at RHIC. It will be this group's responsibility to provide characterizations and calibrations of the multi-anode photomultiplier tubes used for particle detection in this new calorimeter.