Isospin dependence of nuclear EMC effect from global QCD analysis

TL;DR

This paper presents a comprehensive global QCD analysis of unpolarized PDFs in light nuclei, revealing isospin-dependent nuclear effects and the necessity of off-shell corrections to explain recent experimental data.

Contribution

It introduces a simultaneous extraction of PDFs and off-shell corrections without prior assumptions, highlighting isospin dependence of the nuclear EMC effect in light nuclei.

Findings

Evidence for nucleon off-shell corrections in $A=3$ nuclei.

Indications of both isoscalar and isovector nuclear effects.

Differences in EMC ratios compared to heavy nuclei extrapolations.

Abstract

We perform a new global QCD analysis of unpolarized parton distribution functions (PDFs) in the nucleon from proton, deuteron and $A=3$ data, including recent measurements of $^3$He/$D$ and $^3$H/$D$ cross section ratios from the MARATHON experiment at Jefferson Lab. Simultaneously inferring the PDFs and nucleon off-shell corrections allows both to be determined consistently, without theoretical assumptions about the isospin dependence of nuclear effects. The analysis provides strong evidence for the need of nucleon off-shell corrections to describe the $A=3$ data, and suggests the presence of both isoscalar and isovector nuclear effects in $A \leq 3$ nuclei. We find that the extracted EMC ratios of nuclear to nucleon structure functions for $A=2$ and 3 differ from those naively extrapolated from heavy nuclei down to low $A$.