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

Results are reported from the HERMES experiment at HERA on a measurement of the neutron spin structure function ~ ( 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 < x < 0.6 and 1 (GeV/c) 2 < Q2 < 15 (GeV/c ) 2. The integral fo~i0623 ~ ( x ) dx evaluated at a fixed Qz of 2.5 (GeV/c ) 2 is -0 .03440.013(stat.)+0.005(syst.). Assuming Regge behavior at low x, the first moment F'~ = f l ~ ( x ) d x is -0 .037 ± 0.013(stat .)±0.005(syst.)±0.006(extrapol.) . (~) 1997 Published by Elsevier Science B.V. PACS: 25.30.Fj; 13.88.+e; 13.60.Hb HERMES Collaboration~Physics Letters B 404 (1997) 383-389 385 Deep inelastic scattering with lepton beams is an important tool for understanding the quark-gluon structure of the nucleon. With polarized beams and targets, the spin structure of the nucleon is probed via scattering of charged leptons from nucleons through the exchange of virtual photons (with energy transfer v and squared four momentum _Q2). Inclusive polarized scattering is characterized by two structure functions: gl (x, Q2) and g2 (x, Q2), with x = Q2/2Mv. The structure function gl is determined from the virtual photon asymmetries Al and A2 via F1 gl = (1 + T 2) [A1 + ' y A 2 ] , (1) where F1 is the unpolarized structure function and y2 = Q2 / v2" In the quark-parton model the structure function g~ is related to the quark-spin distributions through 1 g,(x,Q2) = g Ze2f[qTf(x, Q2) q } ( x , Q2)l, (2)