Constraints on the large-x d/u ratio from electron-nucleus scattering at x>1

Recently the ratio of neutron to proton structure functions F2n/F2p 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 F2n is usually extracted. The IMC data determine the resulting proton d/u quark distribution ratio, extrapolated to x = 1, to be 0.23 ± 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.