Relative difference between up and down quark structure of the proton

Mingzhe Xie; Siqi Yang; Wenhao Ma; Minghui Liu; Liang Han; C. -P. Yuan

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arXiv · 2505.17608

Relative difference between up and down quark structure of the proton

Mingzhe Xie·Siqi Yang·Wenhao Ma·Minghui Liu·Liang Han·C. -P. Yuan

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Abstract

We presen a novel determination of the down-to-up composition ratio using the forward-backward asymmetry observed in the proton-proton collisions at the LHC. This method offers unique insights into the flavor-specific difference between down and up quarks, which are difficult to isolate in traditional cross-section measurements due to the inherent mixing of contributions from both flavors. In this study, we systematically measure the down-to-up quark ratio over a broad momentum fraction (x) range of 0.01 to 0.1, utilizing the sensitivity of the forward-backward asymmetry to quark-level couplings. Our findings reveal significant deviations in both the value and x-dependence of this ratio compared to predictions from current parton distribution functions (PDFs). These discrepancies highlight potential limitations in existing PDF parameterization and emphasize the importance of flavor-separated measurements for advancing our understanding of proton structure.

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Mingzhe Xie, Siqi Yang, Wenhao Ma, Minghui Liu, Liang Han, C. -P. Yuan. 2025-05-23. Relative difference between up and down quark structure of the proton. https://arxiv.org/abs/2505.17608

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