Parity Violating Electron Scattering at Jefferson Lab

Louisiana Tech University, Ruston LA

Investigators

Abstract

The members of Louisiana Tech University's Center for Applied Physics Studies (CAPS) are deeply involved in the current and future parity violation experiments at Jefferson lab. The Group's primary experimental involvements are the study of the substructure of the proton as members of the G0 experiment, and testing the basic theory of modern physics, the Standard Model, as members of the newly approved Qweak experiment. They are also developing their own scientific program as spokespersons for the E01-115 experiment which will measure the parity violating asymmetry in the reaction when the proton is excited into its first resonant state, the Delta. The experiment will be performed using the G0 apparatus in its backward angle mode, and will probe an important component of the proton's structure, a quantity known as the axial vector transition form factor, inaccessible in other reactions. This form factor measures the contribution of the proton's intrinsic spin to the dynamics of this transition. To facilitate the backward angle measurements for both the G0 elastic and N --> Delta experiments, Louisiana Tech is working on the design, installation, and testing of the Cryostat Exit Detectors (CED's) which also includes development of the associated signal processing electronics. Commissioning for the G0 forward angle measurements has been completed, and the next set of measurements is scheduled to be run in October of 2003. The backward angle measurements are expected to start early in 2005. The Group has taken on a crucial role in the Qweak experiment which will search for physics beyond the standard model by measuring the proton's weak charge. Since the inception of the Qweak experiment, the CAPS Group has been working on the design of major components and attributes of the spectrometer and detector systems. The Group's responsibilities for the upcoming experiment will be the design, testing, construction, and installation of a component of the forward tracking system which will play a crucial role in measuring the kinematics and background of the experiment. These new detectors will be based on the innovative technology of Gas Electron Multiplication (GEMs) which have been recently developed at CERN. To continue Louisiana Tech's program of parity violation measurements, the group submitted an Letter of Intent to the JLab PAC to extend its own program of measurements of the the parity violating asymmetry in the N --> Delta transition at forward angles. This experiment will measure a fundamental coupling constant of dynamic theories of the weak interaction of hadrons, and will also test symmetry breaking mechanisms which take place at higher energies. The involvement of CAPS in modern experiments is not unnoticed in North Louisiana. It is motivation and opportunity for students at all levels in this region to participate in state of the art science. It also provides an opportunity to involve local high school teachers in forefront science and, through their involvement, spread modern science and technology even further into the local student population. This component of the CAPS program is considered as important as their scientific contributions.