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Fluctuations and Correlations of Quark Spin in Hot and Dense QCD Matter

Hao-Lei Chen (陈浩磊)1,2,*, Wei-jie Fu (付伟杰)3,2,†, Xu-Guang Huang (黄旭光)4,1,2,‡, and Guo-Liang Ma (马国亮)1,2,§

  • 1Key Laboratory of Nuclear Physics and Ion-beam Application (MOE), Fudan University, Shanghai 200433, China
  • 2Shanghai Research Center for Theoretical Nuclear Physics, NSFC and Fudan University, Shanghai 200438, China
  • 3School of Physics, Dalian University of Technology, Dalian 116024, China
  • 4Physics Department and Center for Particle Physics and Field Theory, Fudan University, Shanghai 200438, China

  • *Contact author: hlchen15@fudan.edu.cn
  • †Contact author: wjfu@dlut.edu.cn
  • ‡Contact author: huangxuguang@fudan.edu.cn
  • §Contact author: glma@fudan.edu.cn
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Phys. Rev. Lett. 135, 032302 – Published 17 July, 2025

DOI: https://doi.org/10.1103/g1bh-85h4

Abstract

In this Letter, we examine the impact of QCD phase transitions on the quark spin fluctuations and correlations. We propose the quark-antiquark correlation, which relates to the vector meson spin alignment and the Λ−Λ¯ correlation, and can be used as a novel probe of the critical end point (CEP) in the QCD phase diagram. Using the Nambu-Jona-Lanisio model, we qualitatively study the properties of quark-antiquark spin correlations. Our findings reveal a peak structure near the CEP of the chiral phase transition, which may serve as an experimental signature of the CEP and account for the non-monotonic behavior of ϕ meson alignment at low collision energies observed recently in experiments.

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Phys. Rev. Lett. 135, 032302– Published 17 July, 2025
  • Received 18 November 2024
  • Revised 13 June 2025
  • Accepted 17 June 2025
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