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Abou Yassine, R.; Adamczewski-Musch, J.; Asal, C.; Becker, M.; Belounnas, A.; Blanco, A.; Blume, C.; Chlad, L.; Chudoba, P.; Ciepał, I.; Dreyer, J.; Esmail, W.A.; Fabbietti, L.; Floersheimer, H.; Friese, J.; Fröhlich, I.; Förtsch, J.; Galatyuk, T.; Gniazdowski, T.; Greifenhagen, R.; Grunwald, M.; Harabasz, S.; Heinz, T.; Höhne, C.; Hojeij, F.; Holzmann, R.; Huck, H.; Idzik, M.; Kämpfer, B.; Kampert, K-H.; Kardan, B.; Kedych, V.; Koenig, I.; Koenig, W.; Kohls, M.; Kolas, J.; Kornakov, G.; Kotte, R.; Kres, I.; Krueger, W.; Kugler, A.; Lalik, R.; Lebedev, S.; Linev, S.; Linz, F.; Lopes, L.; Lorenz, M.; Malige, A.; Markert, J.; Matulewicz, T.; Maurus, S.; Metag, V.; Michel, J.; Müntz, C.; Nabroth, M.; Naumann, L.; Nowakowski, K.; Orliński, J.; Otto, J.-H.; Parschau, M.; Pechenov, V.; Pechenova, O.; Pfeifer, D.; Piasecki, K.; Pietraszko, J.; Prozorov, A.; Przygoda, W.; Pysz, K.; Ramstein, B.; Rathod, N.; Ritman, J.; Rodriguez-Ramos, P.; Rost, A.; Rustamov, A.; Salabura, P.; Saraiva, J.; Schild, N.; Schwab, E.; Scozzi, F.; Seck, F.; Selyuzhenkov, I.; Singh, U.; Skorpil, L.; Spies, S.; Stefaniak, M.S.; Ströbele, H.; Stroth, J.; Sumara, K.; Svoboda, O.; Szala, M.; Tlusty, P.; Traxler, M.; Wagner, V.; Wasiluk, M.; Weber, A.A.; Wendisch, C.; Wirth, J.; Zherebtsova, E.; Zielinski, M.; Zumbruch, P.
Physics letters. B, 12/2022, Volume: 835Journal Article
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 sNN=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 (pT) and rapidity (yCM) for the range of centrality 0–40%. We observe a strong centrality dependence of the polarization with an increasing signal towards peripheral collisions. For mid-central (20 – 40%) collisions the polarization magnitudes are 〈PΛ〉(%)=6.8±1.3(stat.)±2.1(syst.) for Au+Au and 〈PΛ〉(%)=6.2±0.4(stat.)±0.6(syst.) for Ag+Ag, which are the largest values observed so far. This observation thus provides a continuation of the increasing trend previously observed by STAR and contrasts expectations from recent theoretical calculations predicting a maximum in the region of collision energies about 3 GeV. The observed polarization is of a similar magnitude as predicted by 3D-fluid-dynamics and the UrQMD plus thermal vorticity model and significantly above results from the AMPT model.
