arXiv · 2207.05160
Measurement of global polarization of {\Lambda} hyperons in few-GeV heavy-ion collisions
Abstract
The global polarization of {\Lambda} 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 \sqrt{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 transverse momentum (p_T) and rapidity (y_{CM}) 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 (%) = 6.8 \pm 1.3 (stat.) \pm 2.1 (syst.) for Au+Au and (%) = 6.2 \pm 0.4 (stat.) \pm 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.
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R. Abou Yassine, J. Adamczewski-Musch, C. Asal, M. Becker, A. Belounnas, A. Blanco, C. Blume, L. Chlad, P. Chudoba, I. Ciepal, M. Cordts, J. Dreyer, W. A. Esmail, L. Fabbietti, H. Floersheimer, P. Fonte, J. Friese, I. Fröhlich, J. Förtsch, T. Galatyuk, T Gniazdowski, R. Greifenhagen, M. Grunwald, M. Gumberidze, S. Harabasz, T. Heinz, C. Höhne, F. Hojeij, R. Holzmann, H. Huck, M. Idzik, B. Kämpfer, K-H. Kampert, B. Kardan, V. Kedych, I. Koenig, W. Koenig, M. Kohls, J. Kolas, G. Kornakov, R. Kotte, I. Kres, W. Krueger, A. Kugler, R. Lalik, S. Lebedev, S. Linev, F. Linz, L. Lopes, M. Lorenz, A. Malige, J. Markert, T. Matulewicz, S. Maurus, V. Metag, J. Michel, A. Molenda, C. Müntz, M. Nabroth, L. Naumann, K. Nowakowski, J. Orliński, J. -H. Otto, M. Parschau, C. Pauly, V. Pechenov, O. Pechenova, D. Pfeifer, K. Piasecki, J. Pietraszko, T. Povar, A. Prozorov, W. Przygoda, K. Pysz, B. Ramstein, N. Rathod, J. Ritman, P. Rodriguez-Ramos, A. Rost, A. Rustamov, P. Salabura, J. Saraiva, N. Schild, E. Schwab, F. Scozzi, F. Seck, I. Selyuzhenkov, U. Singh, L. Skorpil, J. Smyrski, S. Spies, M. S. Stefaniak, H. Ströbele, J. Stroth, K. Sumara, O. Svoboda, M. Szala, P. Tlusty, M. Traxler, V. Wagner. 2022-07-11. Measurement of global polarization of {\Lambda} hyperons in few-GeV heavy-ion collisions. https://doi.org/10.1016/j.physletb.2022.137506
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