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

TL;DR

This paper uses electron-nucleus scattering data at high x to constrain the neutron-to-proton structure function ratio, providing insights into the proton's d/u quark distribution at x=1, with implications for nuclear models.

Contribution

It introduces a phenomenological method linking the EMC effect to nuclear effects in deuteron structure functions, constraining the d/u ratio at high x.

Findings

The d/u ratio at x=1 is approximately 0.23 with uncertainty.

The results challenge the scalar diquark dominance limit of 0.

The data suggest a deviation from SU(6) symmetry predictions.

Abstract

Recently the ratio of neutron to proton structure functions F_2n/F_2p 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_2n 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.