Doubling down on proton structure: what double parton scattering can and cannot tell us about partonic separation

Andrew Fowlie; Arthur Moraes; Hao Yang

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arXiv · 2609.11196

Doubling down on proton structure: what double parton scattering can and cannot tell us about partonic separation

Andrew Fowlie·Arthur Moraes·Hao Yang

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Abstract

Double parton scattering provides a unique probe of proton structure and is commonly characterized by the effective cross section $\sigma_\mathrm{eff}$. We examine, under the factorized ansatz for the double-parton-scattering cross section and without assuming any specific parametric form for the transverse profile, what the effective cross section can reveal about the transverse separation, $r$, between partons in the proton. We derive a sharp lower bound on the transverse partonic separation, $\langle r^2\rangle \ge 4\sigma_\mathrm{eff}/(9\pi)$, and demonstrate through explicit counterexamples that previously posited upper bounds do not hold. Our results establish, within the effective-cross-section parametrization of double parton scattering framework, that $\sigma_\mathrm{eff}$ can provide a sharp lower bound on partonic separation but cannot provide a general upper bound.

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Andrew Fowlie, Arthur Moraes, Hao Yang. 2026-09-10. Doubling down on proton structure: what double parton scattering can and cannot tell us about partonic separation. https://arxiv.org/abs/2609.11196

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