Isovector EMC effect from global QCD analysis with MARATHON data

TL;DR

This study performs a comprehensive QCD analysis incorporating MARATHON data, revealing evidence for an isovector EMC effect in light nuclei and challenging existing assumptions about nuclear effects on the d-quark PDF.

Contribution

First global QCD analysis including MARATHON data, indicating an isovector nuclear EMC effect in light nuclei and questioning previous nuclear PDF assumptions.

Findings

Evidence for isovector nuclear EMC effect in light nuclei

MARATHON data suggest enhanced nuclear effect on d-quark PDF

Weak constraints on neutron/proton structure function ratio from MARATHON data

Abstract

We report the results of a Monte Carlo global QCD analysis of unpolarized parton distribution functions (PDFs), including for the first time constraints from ratios of $^3$He to $^3$H structure functions recently obtained by the MARATHON experiment at Jefferson Lab. Our simultaneous analysis of nucleon PDFs and nuclear effects in $A=2$ and $A=3$ nuclei reveals the first indication for an isovector nuclear EMC effect in light nuclei. We find that while the MARATHON data yield relatively weak constraints on the $F_2^n/F_2^p$ neutron to proton structure function ratio and on the $d/u$ PDF ratio, they suggest an enhanced nuclear effect on the $d$-quark PDF in the bound proton, questioning the assumptions commonly made in nuclear PDF analyses.