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arXiv · 2610.31290

Extraction of transverse-momentum-dependent helicity distributions of the nucleon

Ke Yang·Tianbo Liu·Bo-Qiang Ma·Peng Sun·Yuxiang Zhao·Yiyu Zhou
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Abstract

We present an updated global analysis of the transverse-momentum-dependent (TMD) helicity distributions of the nucleon from measurements of the longitudinal double-spin asymmetry $A_{LL}$ in semi-inclusive deep-inelastic scattering (SIDIS). The analysis incorporates target- and detected-hadron-mass corrections, next-to-next-to-leading-order matching in the small-$b_T$ operator product expansion, and an improved treatment of correlated systematic uncertainties. The present data constrain the up- and down-quark helicity TMDs, whereas the sea-quark and gluon distributions remain weakly constrained. After integration over transverse momenta up to the hard scale, the up- and down-quark distributions agree with collinear helicity distributions within uncertainties. Using the extracted TMDs and the Wandzura-Wilczek-type approximation, we predict the $\cosϕ_h$ modulation of $A_{LL}$ and find agreement with the HERMES and CLAS measurements. We also provide predictions for SIDIS $A_{LL}$ at CLAS12 and for longitudinal single-spin asymmetries in $W^\pm$ production with leptonic decays at STAR kinematics. An impact study with pseudodata for the proposed Electron-Ion Collider in China (EicC) indicates substantial potential to improve constraints on helicity TMDs at intermediate $x$, including the presently weakly constrained sea-quark sector.

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Ke Yang, Tianbo Liu, Bo-Qiang Ma, Peng Sun, Yuxiang Zhao, Yiyu Zhou. 2026-10-22. Extraction of transverse-momentum-dependent helicity distributions of the nucleon. https://arxiv.org/abs/2610.31290

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