Precision Determination of the Neutron Spin Structure Function g1n

Abstract

We report on a precision measurement of the neutron spin structure function $g_1^n$ using deep inelastic scattering of polarized electrons by polarized ^3He. For the kinematic range 0.014<x<0.7 and 1 (GeV/c)^2< Q^2< 17 (GeV/c)^2, we obtain ${\int }_{0.014}^{0.7}{g}_1^n(x)dx=-0.036\pm 0.004(stat)\pm 0.005(syst)$ at an average $Q^2=5(GeV/c{)}^2$. We find relatively large negative values for $g_1^n$ at low $x$. The results call into question the usual Regge theory method for extrapolating to x=0 to find the full neutron integral ${\int }_0^1{g}_1^n(x)dx$, needed for testing quark-parton model and QCD sum rules.

5 pages, 3 figures To be published in Phys. Rev. Lett