Overview

The experiment E99-117 was proposed to measure the neutron spin asymmetry $A_1^n$ in inclusive deep inelastic electron scattering at 6 GeV for three kinematics: $0.33<x<0.61$ at $2.7<Q^2<4.9 (GeV/c)^2$ . Available models give different predictions for the high $x$ behavior of $A_1^n$, most of which predict that $A_1^n$ to be large and positive as $x\rightarrow 1$. While all existing data do not yet exhibit this behavior for $x<0.4$, this measurement should clarify the high $x$ behavior of $A_1^n$ and therefore will provide nontrivial experimental support for understanding spin structure of the nucleon.

The experiment will use an 80% polarized electron beam with current 15 $\mu A$ and the beam energy 6 GeV. The target is polarized $^3$He gas cell. Typical target pressure is 10 atm and polarization is 40%. During measurement the target will be polarized either parallel or perpendicular to the electron beam, such that $A_1^n$ can be extracted from the measured asymmetries $A_\parallel$ and $A_\perp$. The two Hall-A high resolution spectrometers will be used in a single mode independent of each other.

The major goal of this run plan is to allocate beam time to different kinematics and different polarization such that the statistical error of each kinematics is minimized to the same level. Electron rates are estimated in section 2, as well as pion and positron backgrounds. Positron runs are found to be necessary. In section 3 all commissionings and other measurements are listed. Finally the overall run plan is summarized in section 4.