%A Zhu-Fang Cui, Fei Gao, Daniele Binosi, Lei Chang, Craig D. Roberts, and Sebastian M. Schmidt %T Valence Quark Ratio in the Proton %0 Journal Article %D 2022 %J Chin. Phys. Lett. %R 10.1088/0256-307X/39/4/041401 %P 041401%V 39 %N 4 %U {https://cpl.iphy.ac.cn/CN/abstract/article_116103.shtml} %8 2022-03-03 %X Beginning with precise data on the ratio of structure functions in deep inelastic scattering (DIS) from $^3$He and $^3$H, collected on the domain $0.19 \leq x_{\scriptscriptstyle{\rm B}} \leq 0.83$, where $x_{\scriptscriptstyle{\rm B}}$ is the Bjorken scaling variable, we employ a robust method for extrapolating such data to arrive at a model-independent result for the $x_{\scriptscriptstyle{\rm B}}=1$ value of the ratio of neutron and proton structure functions. Combining this with information obtained in analyses of DIS from nuclei, corrected for target-structure dependence, we arrive at a prediction for the proton valence-quark ratio: $\left. d_v/u_v \right|_{x_{\scriptscriptstyle{\rm B}}\to 1} = 0.230 (57)$. Requiring consistency with this result presents a challenge to many descriptions of proton structure.