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.