Preliminary results from a Jefferson Lab (JLab) experiment on electron deep inelastic scattering (DIS) off the $^3H$ and $^3He$ mirror nuclei will be presented. The experiment (MARATHON, “MeAsurement of the $F_2^n/F_2^p$, d/u RAtios and A=3 EMC Effect in Deep Inelastic Electron Scattering Off the Tritium and Helium MirrOr Nuclei”) completed data taking in Spring 2018, using the JLab 11 GeV electron beam and the Hall A spectrometer facility. It has measured the DIS cross section ratios for $^2H$, $^3H$ and $^3He$ to determine the ratio of the $F_2^n/F_2^p$ structure functions of the neutron and proton with a novel method which is free of theoretical uncertainties presented in previous SLAC measurements, and extract the d/u ratio of the up and down quark probability distributions in the proton. The results are expected to test the predictions of the quark model of the nucleon and perturbative QCD, and to constrain the parameterizations of nucleon’s parton distribution functions used in the interpretation of high energy collider data. Another goal of the experiment is to precisely measure the EMC effect of the two A=3 mirror nuclei. The results are considered essential for understanding the EMC effect, which describes the modification of the nucleon structure functions in the nuclear medium.
∗On the behalf of MARATHON Collaboration.