Intermediate Energy Nuclear Physics with Electromagnetic Probes at Jefferson Lab

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The present NSF grant primarily funds the RPI group's participation in the the physics program of the Thomas Jefferson National Accelerator Facility, where it is a member of the CLAS Collaboration. The experimental program's goal is to learn about and image the composition of protons and neutrons - generically called nucleons - which comprise nearly all the currently visible matter in the universe. Nucleons are composed of very complicated arrays of quarks immersed in the strong nuclear fields called gluons. The main instrument used is the CLAS spectrometer, inside of which a beam of electrons from the Jefferson Lab accelerator impinges upon a target of protons. Most often the target is in the form of liquid hydrogen atoms. The experiments in which the RPI group are focusing are those in which an electron in the beam strikes and scatters off a proton and part of the energy imparted to the proton produces either a single photon (a quantum of electromagnetic radiation), or a single meson, which is a particle consisting of a quark and antimatter quark pair. By studying this reaction as the imparted energy and direction of the scattered electron is varied, the group seeks to obtain a three dimensional image of the distributions of the quarks in the proton, which has never yet been accomplished. During this grant period the group will continue work on a new CLAS spectrometer, called CLAS12, which is part of the ongoing project at Jefferson Lab to double the energy of the electron beam. The component of the CLAS12 spectrometer on which the RPI is specifically contributing is called a high threshold Cherenkov counter (HTCC), which will be used to identify the scattered electrons. This is in addition to the more general role the Principal Investigator plays in the upgrade as chairman of the CLAS12 steering committee. RPI is a technology based university whose primary goal is to prepare future scientists and engineers for the most advanced technological demands of society. The complexity of the experiments in this research require the development and use of the most advanced scientific equipment and computational techniques. RPI graduate and undergraduate students, as well as post-doctoral associates, participate one way or another in programs such as this, and in the present case directly carry out most of the direct work on the experimental program, enabling them to become the scientific and engineering leaders of a technologically competitive society.