Measurement of global polarization of Λ hyperons in few-GeV heavy-ion collisions

Yassine, R. Abou; Adamczewski-Musch, J.; C., Asal,; Becker, Marten; Belounnas, A.; Blanco, A.; Blume, C.; Chlad, L.; Chudoba, P.; Ciepał, I.; Cordts, Malte; Dreyer, J.; Esmail, W.; Fabbietti, L.; Floersheimer, Henrik; Fonte, P.; Friese, J.; Fröhlich, I.; Förtsch, J.; Galatyuk, T.; Gniazdowski, Tomasz; Greifenhagen, R.; Grunwald, M.; Gumberidze, M.; Harabasz, S.; Heinz, T.; Höhne, C.; Hojeij, Fatima; Holzmann, R.; Huck, Holger; Idzik, M.; Kämpfer, B.; Kampert, K.H.; Kardan, B.; Kedych, V.; Köenig, I.; Koenig, W.; Kohls, M.; Jędrzej, Kołaś,; Kornakov, G.; Kornas, F.; Kötte, R.; Kres, I.; Krueger, Wilhelm; Куглер, А.; Lalik, R.; Lebedev, S.; Linev, S.; Lopes, L.; Lorenz, M.; Malige, A.; Markert, J.; Matulewicz, T.; Maurus, S.; Metag, V.; Michel, J.; Molenda, Aleksandra; Müntz, C.; Nabroth, M.; Naumann, L.; Nowakowski, K.; Orliński, Jan; Otto, Jan-Hendrik; Parschau, M.; Pauly, Christian; Pechenov, V.; Pechenova, O.; Pfeifer, D.; Piasecki, Krzysztof; Pietraszko, J.; Povar, Tetiana; Prozorov, A.; Przygoda, W.; Pysz, K.; Ramstein, B.; Rathod, N.; Ritman, J.; Rodríguez-Ramos, P.; Rost, A.; Rustamov, A.; Salabura, P.; Saraiva, J. de Carvalho; Schild, Niklas; Schwab, E.; Scozzi, F.; Seck, F.; Selyuzhenkov, I.; Singh, U.N.; Skorpil, L.; Smyrski, J.; Spies, S.; Stefaniak, M.; Ströbele, H.; Stroth, J.; Sumara, K.; Svoboda, O.; Szala, M.; Tlustý, P.; Traxler, M.; Wagner, V.; Wasiluk, M.; Weber, A.A.; Wendisch, C.; Wirth, J.; Zbroszczyk, H.; Zherebtsova, E. S.; Zieliński, Marcin; Zumbruch, P.

doi:10.1016/j.physletb.2022.137506

Cited by 21 publications

(9 citation statements)

References 38 publications

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“…Remarkably, a splitting between Λ and Λ polarization signals was successfully described within the UrQMD transport model [22] where it was attributed to the different space-time distributions of Λ and Λ and by different freeze-out conditions of both hyperons. These calculations can also quantitatively describe the centrality dependence of Λ polarization measured by HADES [23].…”

Section: Introductionmentioning

confidence: 93%

“…This mechanism implemented in hydrodynamic [11][12][13][14][15][16] and transport models [17][18][19][20][21][22] allows to reproduce the measured Λ polarization. However, it is still difficult to explain the large Λ polarization observed by the HADES collaboration [23] at low colliding energies √ s NN ∼ 2.5 GeV, see Figure 3 in [23]. Furthermore, most of the above works could not explain the larger polarization of Λs compared to Λs if a special mechanism distinguishing particles from anti-particles is not included, see, e.g., [16,24].…”

Section: Introductionmentioning

confidence: 99%

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Λ and Λ¯ Freeze-Out Distributions and Global Polarizations in Au+Au Collisions

2023

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The gold–gold collisions at sNN=7.7 and 11.5 GeV are simulated within the PHSD transport model. In each collision event, the spectator nucleons are separated and the fluidization procedure for the participants is performed. The local velocities are determined in the Landau frame and the kinematic and thermal vorticity fields are evaluated. We analyze the thermodynamic properties of the cells where Λs and Λ¯s were born or had their last interaction. Such cells contribute to the formation of the observed global polarization of hyperons induced by the thermal vorticity of the medium. The Λ¯ polarization signal is found to be mainly determined by hot, dense, and highly vortical cells at the earlier stage of the collision, whereas the Λ polarization signal is accumulated over the longer time and includes cells with lower vorticity. The calculated global polarizations for both Λs and Λ¯s agree well with the experimental finding by the STAR collaboration at energy sNN=11.5 GeV. For collisions at sNN=7.7 GeV, we can reproduce the STAR data for Λ hyperons, but significantly underpredict the observed global polarization of Λ¯. Furthermore, we consider the centrality dependence of the hyperon polarization in collisions at 7.7 GeV. It increases with an increase of centrality, reaches a maximum at 65–75% and then starts decreasing rapidly for peripheral collisions.

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Section: Introductionmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 99%

Λ and Λ¯ Freeze-Out Distributions and Global Polarizations in Au+Au Collisions

2023

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“…Nowadays, the study of hyperon global polarization is an integral part of the QGP characterization program, linked to QGP properties such as viscosity, vorticity and flow. Recent results on global hyperon polarization, reported by STAR and HADES, for mid-central heavy-ion collisions, show that the global polarization increases with the decrease of collision energy, and that this effect is larger for Λs than for Λs [2][3][4].…”

Section: Introductionmentioning

confidence: 99%

Core-corona approach to describe hyperon global polarization in semi-central relativistic heavy-ion collisions

Ayala,

Domínguez,

Maldonado Cervantes

et al. 2023

Supl. Rev. Mex. Fis.

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We report on the core-corona model developed to describe the main features of hyperon global polarization in semicentral relativistic heavy-ion collisions as a function of the collision energy. We first neglect the contribution to polarization from hyperons produced in the corona. In this scenario, the global polarization turns out to be described by a delicate balance between the vorticity-to-spin transferring reactions in the core and the predominance of corona over core matter at low energies. We show how this last feature provides a key ingredient missing in our original model that helps to better describe the excitation function for Λ and Λ global polarization. To improve the description, we then introduce the contribution to the global polarization coming from the transverse polarization of Λs produced in the corona, which is hereby assumed to be similar to the well-known polarization produced in p + p reactions. The results show a small positive contribution to the global polarization, however they are not yet conclusive due to the small size of the MC sample used in the analysis.

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“…These extreme physical conditions may lead, similarly to the non-relativistic magneto-mechanical effects of Einstein-de Haas [6] and Barnett [7], to spin polarization and magnetization of the matter and, consequently, of the emitted particles [8][9][10]. The existence of spin polarization phenomenon was recently confirmed experimentally [11][12][13][14][15][16][17] triggering vast theoretical developments aiming at finding a unified interpretation of the measured observables [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]. In particular, based on fundamental conservation laws, an extension of relativistic hydrodynamics for spin-polarized fluids was proposed [37] giving rise to the rapid development of a new field known as relativistic spin hydrodynamics [38][39][40][41][42][43][44][45][46][47][48][49][50]…”

Section: Introductionmentioning

confidence: 99%

Relativistic Spin Magnetohydrodynamics

et al. 2022

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In this work, we present a novel framework of relativistic non-resistive dissipative magnetohydrodynamics for spin-polarized particles. Utilizing a classical relativistic kinetic equation for the distribution function in an extended phase-space of position, momentum, and spin, we derive equations of motion for dissipative currents at first-order in spacetime gradients. Our findings reveal a coupling between fluid vorticity and magnetization via an electromagnetic field, leading to relativistic analogs of the Einstein-de Haas and Barnett effects. Our study provides a tool for a better understanding of the polarization phenomena observed in relativistic heavy-ion collisions.

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Measurement of global polarization of Λ hyperons in few-GeV heavy-ion collisions

Cited by 21 publications

References 38 publications

Λ and Λ¯ Freeze-Out Distributions and Global Polarizations in Au+Au Collisions

Λ and Λ¯ Freeze-Out Distributions and Global Polarizations in Au+Au Collisions

Core-corona approach to describe hyperon global polarization in semi-central relativistic heavy-ion collisions

Relativistic Spin Magnetohydrodynamics

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