High x Structure Function of the Virtually Free Neutron

TL;DR

This paper uses pole extrapolation in electron scattering experiments to measure the neutron's high-x structure function, revealing a potential rise in the neutron-to-proton ratio at high x, which could suggest new quark dynamics.

Contribution

It introduces a model-independent pole extrapolation method to extract neutron structure functions from deuteron scattering data.

Findings

Neutron structure functions show a surprising rise at high x.

Potential indication of new quark dynamics in the nucleon.

Possible dominance of short-range quark-quark correlations.

Abstract

The pole extrapolation method is applied to the semi-inclusive inelastic electron scattering off the deuteron with tagged spectator protons to extract the high-x structure function of the neutron. This approach is based on the extrapolation of the measured cross sections at different momenta of the spectator proton to the non-physical pole of the bound neutron in the deuteron. The advantage of the method is in the possibility of suppression of the nuclear effects in a maximally model-independent way. The neutron structure functions obtained in this way demonstrate a surprising x dependence at $x\ge 0.6$ and $1.6 \leq Q^2 \leq 3.38$ GeV$^2$, indicating a possible rise of the neutron to proton structure function ratio. If the observed rise is valid in the true deep inelastic region then it may indicate new dynamics in the generation of high-x quarks in the nucleon. One such mechanism we discuss is the possible dominance of short-range isosinglet quark-quark correlations that can enhance the d-quark distribution in the proton.