A precision measurement of the twist-3 matrix element d(2) and spin structure function g(2) for the proton and deuteron

The polarized spin structure functions $gp2$ and $gd2$ have been measured at SLAC via the process of deep inelastic scattering. The data were collected over the kinematic range 0.02 ≤ x ≤ 0.8 and 0.7 (GeV/c)2 ≤ Q2 ≤ 20 (GeV/c) 2 by scattering 29.1 and 32.3 GeV longitudinally polarized electrons from transversely polarized 15NH₃ and 6LiD targets. This is the first data set for $gp2$ with sufficient precision to differentiate between current theoretical models for the proton. The data show that $gp2$ is consistant with $gWW2$ as well as the bag model of Strattman and the Chiral model of Weigel while showing that it is inconsistent by several sigma with g ₂ = 0 in the region x > 0.2. The absolute value of A₂ is significantly smaller than the $R$ positivity limit over the measured range and is also within the Soffer limit. The results for the twist-3 reduced matrix elements $dp2$, $dd2$ and $dn2$ are also obtained. The Burkhardt-Cottingham sum rule integral and the Efremov-Leader-Taryaev sum rule integral are reported for the experimental kinematic range.