Precision Measurements of $A_1^n$ in the Deep Inelastic Regime

Abstract

We have performed precision measurements of the double-spin virtual-photon asymmetry $A_1$ on the neutron in the deep inelastic scattering regime, using an open-geometry, large-acceptance spectrometer. Our data cover a wide kinematic range $0.277\le x\le 0.548$ at an average $Q^2$ value of 3.078~(GeV/c)${}^2$, doubling the available high-precision neutron data in this $x$ range. We have combined our results with world data on proton targets to extract the ratio of polarized-to-unpolarized parton distribution functions for up quarks and for down quarks in the same kinematic range. Our data are consistent with a previous observation of an $A_1^n$ zero crossing near $x=0.5$. We find no evidence of a transition to a positive slope in $(\hat{I}”d+\hat{I}”\bar{d})/(d+\bar{d})$ up to $x=0.548$.

6 pages, 2 figures, 3 tables. Two typos corrected in Table 3