Measurement of the neutron spin structure function gn1 with a polarized 3 He internal target

Results are reported from the HERMES experiment at HERA on a measurement of the neutron spin structure function g 1 n ( x, Q 2 ) in deep inelastic scattering using 27.5 GeV longitudinally polarized positrons incident on a polarized 3 He internal gas target. The data cover the kinematic range 0.023 c ) 2 Q 2 c ) 2 . The integral ∫ 0.6 0.023 g 1 n ( x ) dx evaluated at a fixed Q 2 of 2.5 (GeV/ c ) 2 is −0.034 ± 0.013(stat.)±0.005(syst.). Assuming Regge behavior at low x , the first moment Г n 1 = ∫ 1 0 g 1 n ( x ) dx is −0.037 ± 0.013(stat.)±0.005(syst.)±0.006(extrapol.).