Dual-polarization structure and nuclear structure effect on $\Lambda$ polarization

TL;DR

This study uncovers how nuclear structure and spin-vorticity interactions influence $ ext{Lambda}$ hyperon polarization in relativistic heavy-ion collisions, revealing sensitivity to nuclear geometry and clustering effects.

Contribution

It demonstrates for the first time the dual-polarization structure of $ ext{Lambda}$ hyperons and their dependence on nuclear configurations in high-energy collisions.

Findings

Distinct polarization patterns for different nuclear geometries.

Opposite polarization distributions in backward rapidity and peripheral events.

Nuclear clustering affects hyperon spin alignment observable in experiments.

Abstract

We report a novel manifestation of spin-vorticity interplay in relativistic heavy-ion collisions. Using $^{16}$O+$^{197}$Au at $\sqrt{s_{\rm NN}}=7.7$ GeV as a test case, we show that the $\Lambda$ hyperon exhibits a clear dual-polarization structure, observed here in central $^{16}$O + $^{197}$Au collisions for the first time. The polarization is further highly sensitive to the intrinsic nuclear geometry: different $\alpha$-cluster configurations of $^{16}$O, ranging from chain-like to tetrahedral, lead to distinct polarization patterns across centralities. In particular, the backward rapidity region and peripheral events display striking structure-dependent variations, including opposite angular distributions of local polarizations $P_x$ and $P_y$ compared with a spherical reference. These findings reveal that nuclear clustering leaves measurable imprints on hyperon spin alignment in relativistic collisions. Our results open a promising avenue for probing nuclear structure in short-lived systems and highlight a new spin-sensitive mechanism relevant for upcoming experiments at RHIC and future facilities.