Constraints on the large-xd/uratio from electron-nucleus scattering atx>1

Abstract

Recently the ratio of neutron to proton structure functions ${F}_{2}^{n}/{F}_{2}^{p}$ was extracted from a phenomenological correlation between the strength of the nuclear EMC effect and inclusive electron--nucleus cross section ratios at $x>1$. Within conventional models of nuclear smearing, this ``in-medium correction'' (IMC) extraction constrains the size of nuclear effects in the deuteron structure functions, from which the neutron structure function ${F}_{2}^{n}$ is usually extracted. The IMC data determine the resulting proton $d/u$ quark distribution ratio, extrapolated to $x=1$, to be $0.23\ifmmode\pm\else\textpm\fi{}0.09$ with a 90% confidence level. This is well below the SU(6) symmetry limit of $1/2$ and significantly above the scalar diquark dominance limit of 0.