Speaker
Description
Nucleon elastic form factors encode crucial information about its charge and magnetization distributions. For many decades, nucleon form factors were studied by using unpolarized electron-nucleon cross section measurements. The advent of electron beams with higher luminosities and beam polarization coupled with large acceptance detectors, polarized targets and recoil polarimeters enabled a wealth of information on nucleon form factors over a broad range of momentum transfer (Q^2). While plenty of information is available on the proton, no data above Q^2 = 3.5 GeV^2 is available on the neutron electric form factor. Pushing the data to a higher Q^2 allows constraining spin flip GPDs and serves as a bench mark for various theoretical models. Using quasi-elastic scattering of a polarized electron beam on a polarized ^3He target, one can extract the GEn term which is proportional to the measured asymmetry from opposite electron beam helicity.
The GEn-II experiment at Jefferson lab utilizes a polarized He3 target for a high Q^2 measurement of the neutron electric form factor. The target consists of a pumping chamber (where polarization of He3 takes place), a target chamber (where e- beam interacts with the target material) and transfer tubes (which facilitate a convective flow of the polarized material). ^3He gas at ~8 atm pressure is filled into the glass cells along with Rb-K alkali mixture and narrow band diode lasers are used for polarizing the He3 using a SEOP (Spin Exchange Optical Pumping) technique. The target system used in the experiment includes multiple Helmholtz coils to create a holding field that determines the direction of polarization for the ^3He nuclei. Two polarimetry techniques are used to determine the absolute (EPR) and relative (EPR) polarization during production running. The GEn-II experiment finished taking data at three out of four kinematic settings and is scheduled for completion in the Fall of this year. A general description of the target and an overall performance will be discussed in this talk.
