Global polarization of $Λ$, $Ξ$, and $Ω$ hyperons in Au+Au collisions from the RHIC Beam Energy Scan-II
Auteurs : STAR Collaboration
Résumé scientifique
Global polarization of $Λ$, $Ξ$, and $Ω$ hyperons is measured in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}=7.7$, 9.2, 11.5, 14.6, 17.3, 19.6, and 27~GeV using high-statistics data from the second phase of the RHIC Beam Energy Scan. No significant difference between the $Λ$ and $\barΛ$ polarizations is observed over the measured collision-energy range, providing improved constraints on magnetic-field-induced contributions. The $Λ$ polarization increases with the magnitude of rapidity, with the slope of the linear fit differing from zero by 4.8 standard deviations, providing the first evidence for a nonzero rapidity dependence of global polarization in this energy range. Global polarization of $Ξ^{-}+\barΞ^{+}$ is observed for the first time at these energies at a significance exceeding 5 standard deviations, with a magnitude comparable to that of $Λ+\barΛ$ and an increase toward lower collision energies. Measurements of $Ω^{-}+\barΩ^{+}$ are compatible with a similar energy dependence and favor the decay parameter $γ_Ω= +1$ with high probability under the assumption of the global polarization picture. These measurements provide new constraints on the energy evolution, rapidity dependence, and species dependence of global polarization in heavy-ion collisions.
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Global Polarization of Ξ and Ω Hyperons in Au+Au Collisions at sqrt[s_{NN}]=200 GeV.J. Adam, L. Adamczyk, J. Adams et al. · 2021 · Physical Review Letters · cité 62 fois · Pas encore résumé
Cette mesure étudie la polarisation globale des hyperons Ξ et Ω dans Au+Au à 200 GeV, tandis que l’article mesure aussi ces espèces à des énergies BES-II plus basses.
Résumé scientifique
Global polarization of Ξ and Ω hyperons has been measured for the first time in Au+Au collisions at sqrt[s_{NN}]=200 GeV. The measurements of the Ξ^{-} and Ξ[over ¯]^{+} hyperon polarization have been performed by two independent methods, via analysis of the angular distribution of the daughter particles in the parity violating weak decay Ξ→Λ+π, as well as by measuring the polarization of the daughter Λ hyperon, polarized via polarization transfer from its parent. The polarization, obtained by combining the results from the two methods and averaged over Ξ^{-} and Ξ[over ¯]^{+}, is measured to be ⟨P_{Ξ}⟩=0.47±0.10(stat)±0.23(syst)% for the collision centrality 20%-80%. The ⟨P_{Ξ}⟩ is found to…
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Differential measurement of global polarization of $\Lambda$, $\Xi$, and $\Omega$ hyperons in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}=7.7$--$27~\mathrm{GeV}$ from the RHIC Beam Energy Scan-IIThe Star Collaboration · 2026 · Pas encore résumé
Cette étude mesure différentiellement la polarisation de Λ, Ξ et Ω dans les mêmes collisions Au+Au et aux mêmes énergies BES-II.
Résumé scientifique
We present high-precision differential measurements of the global polarization of $\Lambda$, $\Xi$, and $\Omega$ hyperons in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}=7.7$, $9.2$, $11.5$, $14.6$, $17.3$, $19.6$, and $27~\mathrm{GeV}$ from the RHIC Beam Energy Scan Phase II (BES-II) using the STAR detector. The results show a clear centrality dependence, with polarization increasing toward more peripheral collisions. Within the present experimental precision, no significant dependence on transverse momentum is observed for $\Lambda$ and $\Xi$, and no significant rapidity dependence is observed for the $\Xi$. The polarization of $\Xi$ hyperons is comparable at the current precision to that o…
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Measurement of global polarization of Λ hyperons in few-GeV heavy-ion collisionsR. Abou Yassine, J. Adamczewski-Musch, C. Asal et al. · 2022 · Physics Letters B · cité 65 fois · Pas encore résumé
Cette mesure étudie la polarisation globale de Λ selon la centralité, le moment transverse et la rapidité, mais dans des collisions à quelques GeV.
Résumé scientifique
The global polarization of Λ hyperons along the total orbital angular momentum of a relativistic heavy-ion collision is presented based on the high statistics data samples collected in Au+Au collisions at √ s NN = 2 . 4 GeV and Ag+Ag at 2.55 GeV with the High-Acceptance Di-Electron Spectrometer (HADES) at GSI, Darmstadt. This is the first measurement below the strangeness production threshold in nucleon-nucleon collisions. Results are reported as a function of the collision centrality as well as a function of the hyperon’s transverse momentum ( p T ) and rapidity ( y CM ) for the range of centrality 0–40%. We observe a
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Global spin polarization of multistrange hyperons and feed-down effect in heavy-ion collisionsHui Li, Xiao-Liang Xia, Xu-Guang Huang et al. · 2021 · Physics Letters B · cité 33 fois · Pas encore résumé
Ce modèle multiphase calcule les polarisations de Λ, Ξ et Ω et leurs effets de feed-down aux énergies Au+Au, contrairement aux mesures expérimentales de l’article.
Résumé scientifique
Global spin polarization of hyperons is an important observable to probe the vorticity of the quark-gluon plasma produced in heavyion collisions. We calculate the global polarizations of Λ, Ξ−, and Ω− in Au+Au collisions at energies √ sNN = 7.7–200 GeV based on a multiphase transport model. Our calculations suggest that their primary global polarizations fulfill PΩ− ' 5/3PΞ− ' 5/3PΛ. We also estimate the feed-down effect of particle decay on the global polarization. With the feed-down effect taken into account, the global polarizations of Λ and Ξ− are clearly separated, and the final global polarizations are in the ordering: PΩ− > PΞ− > PΛ. Such a relation can be tested in experiments, which…
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Hyperon global polarization in heavy-ion collisions at energies available at the JINR Nuclotron-based Ion Collider fAcility: Feed-down effects and the role of Σ0 hyperonsV. Voronyuk, N. Tsegelnik, E. Kolomeitsev · 2023 · Physical Review C · cité 4 fois · Pas encore résumé
Ce calcul PHSD examine la polarisation des hyperons et les effets de feed-down à basse énergie, plutôt que de la mesurer dans les données BES-II.
Résumé scientifique
Global polarization of hyperons induced by the local vorticity of the medium created in heavy-ion collisions at energies 2.3\,GeV$\le\sqrt{s_{NN}}\le$11.5 GeV is calculated in the parton-hadron-string dynamic (PHSD) model. The separation of spectator nucleons and the fluidization of the generated particle distributions are performed. The polarization of all anti-hyperon species is found significantly larger than that of hyperons. The $\overline{\Xi}$ hyperons are found to be polarized as strong as $\overline{\Lambda}$s but $\Xi$ hyperons have weaker polarization compared to $\Lambda$s. The $\Omega$ and $\overline{\Omega}$ polarizations show the strongest dependence on the collision energy. D…
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Hyperon global polarization in isobar Ru+Ru and Zr+Zr collisions at $\sqrt{s_{NN}}$ = 200 GeVThe Star Collaboration · 2025 · cité 3 fois · Pas encore résumé
Cette mesure STAR compare les polarisations de Λ et Ξ selon la centralité dans Ru+Ru et Zr+Zr à 200 GeV, plutôt que dans Au+Au au BES-II.
Résumé scientifique
The polarization of Lambda, Anti-Lambda, Xi, and Anti-Xi hyperons along the angular momentum of the system has been measured in isobar collisions of Ru+Ru and Zr+Zr at $\sqrt{s_{NN}}$ = 200 GeV with the STAR detector at RHIC. The polarization dependence on collision centrality is explored and found to show an increasing trend in more peripheral collisions. Dependencies on transverse momentum and pseudorapidity are investigated for Lambda and Anti-Lambda hyperons, but no significant dependence has been observed. The polarization measurements for Lambda and Anti-Lambda are consistent with each other, indicating little contribution of the spin-magnetic coupling in the observed polarization. The…
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Global polarization measurement in Au+Au collisionsB. Abelev, M. Aggarwal, Z. Ahammed et al. · 2006 · cité 134 fois · Pas encore résumé
Cette mesure STAR étudie les polarisations globales de Λ et anti-Λ en Au+Au, notamment à 62,4 et 200 GeV, et trouve des résultats compatibles avec zéro.
Résumé scientifique
The system created in non-central relativistic nucleus-nucleus collisions possesses large orbital angular momentum. Due to spin-orbit coupling, particles produced in such a system could become globally polarized along the direction of the system angular momentum. We present the results of Lambda and anti-Lambda hyperon global polarization measurements in Au+Au collisions at sqrt{s_NN}=62.4 GeV and 200 GeV performed with the STAR detector at RHIC. The observed global polarization of Lambda and anti-Lambda hyperons in the STAR acceptance is consistent with zero within the precision of the measurements. The obtained upper limit, |P_{Lambda,anti-Lambda}|<= 0.02, is compared to the theoretical va…
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Is different Λ and Λ¯ polarization caused by different spatio-temporal freeze-out picture?O. Vitiuk, L. Bravina, E. Zabrodin · 2020 · Physics Letters B · cité 40 fois · Pas encore résumé
Ce modèle UrQMD calcule les polarisations de Λ et anti-Λ et attribue leur différence aux distributions spatio-temporelles et aux conditions de gel, contrairement à la mesure expérimentale.
Résumé scientifique
Abstract Thermal vorticity in non-central Au+Au collisions at energies 7.7 ≤ s ≤ 62.4 GeV is calculated within the UrQMD transport model. Tracing the Λ and Λ ¯ hyperons back to their last interaction point we were able to obtain the temperature and the chemical potentials at the time of emission by fitting the extracted bulk characteristics of hot and dense medium to statistical model of ideal hadron gas. Then the polarization of both hyperons was calculated. The polarization of Λ and Λ ¯ increases with decreasing energy of nuclear collisions. The stronger polarization of Λ ¯ is explained by the different space-time distributions of Λ and Λ ¯ and by different freeze-out conditions of both hy…
Les travaux antérieurs sur lesquels il s’appuie
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Globally polarized quark-gluon plasma in noncentral A + A collisions.Zuo-Tang Liang, Xin-Nian Wang · 2004 · Physical Review Letters · cité 403 fois · Pas encore résumé
Ce travail propose que le couplage spin-orbite polarise les quarks dans les collisions non centrales, mécanisme qui motive l’étude de la polarisation globale des hyperons.
Résumé scientifique
Produced partons have a large local relative orbital angular momentum along the direction opposite to the reaction plane in the early stage of noncentral heavy-ion collisions. Parton scattering is shown to polarize quarks along the same direction due to spin-orbital coupling. Such global quark polarization will lead to many observable consequences, such as left-right asymmetry of hadron spectra and global transverse polarization of thermal photons, dileptons, and hadrons. Hadrons from the decay of polarized resonances will have an azimuthal asymmetry similar to the elliptic flow. Global hyperon polarization is studied within different hadronization scenarios and can be easily tested.
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Spin polarization in relativistic heavy-ion collisionsF. Becattini, Matteo Buzzegoli, T. Niida et al. · 2024 · International Journal of Modern Physics E · cité 53 fois · Pas encore résumé
Cette revue présente les mesures de polarisation globale et locale des hyperons ainsi que les cadres théoriques du domaine étudié par l’article.
Résumé scientifique
Polarization has opened a new physics chapter in relativistic heavy-ion collisions. Since the first prediction and experimental observation of global spin polarization, a lot of progress has been made in understanding its features, both at experimental and theoretical levels. In this paper, we give an overview on the recent advances in this field. The covered topics include a review of measurements of global and local spin polarization of hyperons and the global spin alignment of vector meson’s. We account for the basic theoretical framework to describe spin polarization in a relativistic fluid such as the Quark–Gluon Plasma, including statistical quantum field theory and local thermodynamic…
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Thermal vorticity and spin polarization in heavy-ion collisionsDe-Xian Wei, Wei-Tian Deng, Xu-Guang Huang · 2018 · Physical Review C · cité 89 fois · Pas encore résumé
Cette étude AMPT calcule l’évolution de la vorticité thermique et les polarisations de Λ et anti-Λ selon l’énergie, la rapidité et d’autres variables.
Résumé scientifique
The hot and dense matter generated in heavy-ion collisions contains intricate vortical structure in which the local fluid vorticity can be very large. Such vorticity can polarize the spin of the produced particles. We study the event-by-event generation of the so-called thermal vorticity in Au + Au collisions at energy region $\sqrt{s}=7.7-200$ GeV and calculate its time evolution, spatial distribution, etc., in a multiphase transport (AMPT) model. We then compute the spin polarization of the $\Lambda$ and $\bar{\Lambda}$ hyperons as a function of $\sqrt{s}$, transverse momentum $p_T$, rapidity, and azimuthal angle. Furthermore, we study the harmonic flow of the spin, in a manner analogous t…
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Local spin polarization in high energy heavy ion collisionsHong-Zhong Wu, L. Pang, Xu-Guang Huang et al. · 2019 · Physical Review Research · cité 54 fois · Pas encore résumé
Cette simulation CLVisc examine la dépendance azimutale de la polarisation locale des hyperons à 200 GeV, plutôt que la polarisation globale mesurée ici.
Résumé scientifique
We revisit the azimuthal angle dependence of the local spin polarization of hyperons in heavy-ion collisions at 200 GeV in the framework of the (3+1)D viscous hydrodynamic model CLVisc. Two different initial conditions are considered in our simulation: the optical Glauber initial condition without initial orbital angular momentum and the AMPT initial condition with an initial orbital angular momentum. We find that the azimuthal angle dependence of the hyperon polarization strongly depends on the choice of the so-called 'spin chemical potential' $\Omega_{\mu\nu}$. With $\Omega_{\mu\nu}$ chosen to be proportional to the temperature vorticity, our simulation shows qualitatively coincidental res…
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Polarization and Vorticity in the Quark–Gluon PlasmaF. Becattini, M. Lisa · 2020 · Annual Review of Nuclear and Particle Science · cité 244 fois · Pas encore résumé
Cette synthèse relie la vorticité du plasma quarks-gluons à la polarisation hadronique et situe les premières mesures de Λ dans ce contexte.
Résumé scientifique
The quark–gluon plasma (QGP) produced by collisions between ultrarelativistic heavy nuclei is well described in the language of hydrodynamics. Noncentral collisions are characterized by very large angular momentum, which in a fluid system manifests as flow vorticity. This rotational structure can lead to a spin polarization of the hadrons that eventually emerge from the plasma, and thus these collisions provide experimental access to flow substructure at unprecedented detail. Recently, the first observations of Λ hyperon polarization along the direction of collisional angular momentum were reported. These measurements are in broad agreement with hydrodynamic and transport-based calculations …
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