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arXiv · 2505.05172

Directed flow from parton spin-orbit coupling in $pp$ and $pA$ collisions

Sanjin Benić·Yoshitaka Hatta
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Abstract

We point out a novel mechanism to generate $\cos \phi$ two-particle azimuthal correlation (`directed flow') in unpolarized proton-proton and proton-nucleus collisions in the forward rapidity region of the projectile proton. This is a direct consequence of the recently discovered strong spin-orbit coupling in gluons at small-$x$. The observable simultaneously serves as a unique probe into the double helicity parton distribution functions of the proton.

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Sanjin Benić, Yoshitaka Hatta. 2025-05-08. Directed flow from parton spin-orbit coupling in $pp$ and $pA$ collisions. https://doi.org/10.1016/j.physletb.2025.139709

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