Measurement of the neutron spin structure function g with a polarized 3He internal target

Results are reported from the HERMES experiment at HERA on a measurement of the neutron spin structure function g1n(x, Q2) in deep inelastic scattering using 27.5 GeV longitudinally polarized positrons incident on a polarized 3He internal gas target. The data cover the kinematic range 0.023 < × < 0.6 and 1 (GeV/c)2 < Q2 < 15 (GeV/c)2. The integral ∫0.60.023 g1n(x) dx evaluated at a fixed Q2 of 2.5 (GeV/c)2 is −0.034 ± 0.013(stat.)±0.005(syst.). Assuming Regge behavior at low x, the first moment Гn1 = ∫10 g1n(x)dx is −0.037 ± 0.013(stat.)±0.005(syst.)±0.006(extrapol.).