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Unraveling proton spin polarization through hypertriton production in heavy-ion collisions

Dai-Neng Liu1,2, Yun-Peng Zheng1,2, Wen-Hao Zhou1,2,3,*, Jin-Hui Chen1,2,†, Che Ming Ko4,‡, Yu-Gang Ma1,2,5,§, Kai-Jia Sun1,2,∥, and Song Zhang1,2,¶

  • 1Key Laboratory of Nuclear Physics and Ion-Beam Application (MOE), Institute of Modern Physics, Fudan University, Shanghai 200433, China
  • 2Shanghai Research Center for Theoretical Nuclear Physics, NSFC and Fudan University, Shanghai 200438, China
  • 3Faculty of Science, Xihang University, Xi’an 710077, China
  • 4Cyclotron Institute and Department of Physics and Astronomy, Texas A&M University, College Station, Texas 77843, USA
  • 5School of Physics, East China Normal University, Shanghai 200241, China

  • *Contact author: zhouwenhao@xaau.edu.cn
  • †Contact author: chenjinhui@fudan.edu.cn
  • ‡Contact author: ko@comp.tamu.edu
  • §Contact author: mayugang@fudan.edu.cn
  • ∥Contact author: kjsun@fudan.edu.cn
  • Contact author: song_zhang@fudan.edu.cn
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Phys. Rev. Research 8, 033057 – Published 13 July, 2026

DOI: https://doi.org/10.1103/dvz5-x9s9

Abstract

Ultrarelativistic nuclear collisions create the quark-gluon plasma known as the hottest, least viscous, and most vortical fluid ever produced in terrestrial laboratories. Its vortical structure has been uncovered through the spin polarization of Lambda (Λ) hyperons, attributed to the spin-orbit coupling that transfers the system’s orbital angular momentum to the quark spin, which is then inherited by hadrons via quark recombination or coalescence. However, Λ polarization reflects primarily the strange-quark component, leaving the spin dynamics of the up and down quarks largely unexplored. Although the proton is an ideal probe, its stability makes direct measurements experimentally challenging. Here, we propose to unravel proton spin polarization via hypertriton (Λ3H) measurements, exploiting the fact that spin information is preserved when polarized nucleons and Λ coalesce to form hypertriton. We show that, over a broad range of collision energies, the polarizations of proton, Λ, and hypertriton are related by a simple linear scaling law. Since both Λ and hypertriton polarizations can be measured via their self-analyzing weak decays, this linear relation provides a practical experimental avenue for accessing spin polarizations of protons and neutrons—the dominant baryonic degrees of freedom in nuclear collisions.

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Phys. Rev. Research 8, 033057– Published 13 July, 2026
  • Received 30 October 2025
  • Accepted 17 June 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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