A precision measurement of the spin structure function g(2)(p)

The spin structure function g2(x, Q2) and the virtual photon asymmetry A 2(x, Q2) were measured for the proton using deep inelastic scattering. The experiment was conducted at the Stanford Linear Accelerator Center (SLAC), where longitudinally polarized electrons at 29.1 and 32.3 GeV were scattered from a transversely polarized NH 3 target. Large data sets were accumulated using three independent spectrometers covering a kinematic range 0.02 ≤ x ≤ 0.8 and 1 ≤ Q2 ≤ 20 (GeV/c)2. This new data is the first data precise enough to distinguish between current models for the proton. The structure function gp2 was found to be reasonably consistent with the twist-2 Wandzura-Wilczek calculation. The Q2 dependence of g2 approximately follows the Q 2 dependence of gWW2 , although the data are not precise enough to rule out no Q2 dependence. The absolute value for Ap2 was found to be significant smaller than the Soffer limit over the measured range. The virtual photon asymmetry A2 was also found to be inconsistent with zero over much of the measured range.