Global $Λ$ hyperon polarization in low-energy heavy ion collisions -- a scenario without vorticity
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arXiv
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| Formato: | Preprint |
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2026
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| _version_ | 1866917354191978496 |
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| author | Liu, Feng Tu, Zhoudunming |
| author_facet | Liu, Feng Tu, Zhoudunming |
| contents | Since its discovery, global polarization of the $Λ$ hyperon in heavy-ion collisions has been firmly established and is widely attributed to the large vorticity generated in the rotating quark-gluon plasma. In contrast, nearly fifty years after the first observation of unexpectedly large transverse $Λ$ polarization in unpolarized hadron collisions, its underlying mechanism remains an open and long-standing puzzle, despite being observed across a broad range of collision systems. Although these two phenomena exhibit notable similarities, they are generally regarded as arising from distinct physical origins. In this work, we propose a direct connection between $Λ$ global polarization in heavy-ion collisions and the long-standing transverse polarization observed in unpolarized collision systems. We demonstrate that the alignment between the $Λ$ production plane and the reaction plane, driven by directed flow, can transfer transverse polarization into the measured global polarization signal. Realistic Monte Carlo simulations of Au+Au collisions at $\sqrt{s_{\rm NN}} = 3$ GeV indicate that this mechanism can generate a sizable global polarization, accounting for approximately $23\%\pm6\%$ of the magnitude reported by the STAR Collaboration. Our results establish, for the first time, a quantitative link between these two well-known phenomena and have important implications for the interpretation of $Λ$ global polarization measurements in low-energy heavy-ion collisions. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2603_19581 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Global $Λ$ hyperon polarization in low-energy heavy ion collisions -- a scenario without vorticity Liu, Feng Tu, Zhoudunming High Energy Physics - Phenomenology High Energy Physics - Experiment Nuclear Experiment Nuclear Theory Since its discovery, global polarization of the $Λ$ hyperon in heavy-ion collisions has been firmly established and is widely attributed to the large vorticity generated in the rotating quark-gluon plasma. In contrast, nearly fifty years after the first observation of unexpectedly large transverse $Λ$ polarization in unpolarized hadron collisions, its underlying mechanism remains an open and long-standing puzzle, despite being observed across a broad range of collision systems. Although these two phenomena exhibit notable similarities, they are generally regarded as arising from distinct physical origins. In this work, we propose a direct connection between $Λ$ global polarization in heavy-ion collisions and the long-standing transverse polarization observed in unpolarized collision systems. We demonstrate that the alignment between the $Λ$ production plane and the reaction plane, driven by directed flow, can transfer transverse polarization into the measured global polarization signal. Realistic Monte Carlo simulations of Au+Au collisions at $\sqrt{s_{\rm NN}} = 3$ GeV indicate that this mechanism can generate a sizable global polarization, accounting for approximately $23\%\pm6\%$ of the magnitude reported by the STAR Collaboration. Our results establish, for the first time, a quantitative link between these two well-known phenomena and have important implications for the interpretation of $Λ$ global polarization measurements in low-energy heavy-ion collisions. |
| title | Global $Λ$ hyperon polarization in low-energy heavy ion collisions -- a scenario without vorticity |
| topic | High Energy Physics - Phenomenology High Energy Physics - Experiment Nuclear Experiment Nuclear Theory |
| url | https://arxiv.org/abs/2603.19581 |