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arXiv · 2610.17624

Octupole parton structure of spin-3/2 targets

Brandon B. Le·Dustin Keller
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Abstract

In spin-$3/2$ targets, octupole polarization can reveal quark and gluon correlations beyond those probed by vector polarization and quadrupole alignment. Here, we construct the complete leading-twist gluon transverse-momentum-dependent distribution basis, with 32 independent coefficients for each specified Wilson-line and color structure. Fourteen of these describe octupole dependence in gluon number, helicity, and linear polarization. In heavy-quark-pair leptoproduction at small, nonzero pair imbalance, comparing target states with opposite octupoles and identical lower moments isolates the octupole contribution. Beam-helicity reversal and joint angular projections in target orientation and pair-imbalance azimuth can then separate all fourteen gluon octupole responses at leading-power Born order. We also derive the incoming-target quark responses in semi-inclusive deep-inelastic scattering and Drell-Yan production. Time-reversal relations between distributions remain valid under symmetry-preserving renormalization and evolution, while predictions across processes require factorization formulas connecting those distributions to scattering observables. Finally, we connect this framework to polarized $^{7}$Li through its collinear limits and nuclear spin-orbital correlations.

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Brandon B. Le, Dustin Keller. 2026-10-13. Octupole parton structure of spin-3/2 targets. https://arxiv.org/abs/2610.17624

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