Global Λ-hyperon polarization in Au plus Au collisions at √SNN=3 GeV

作者：Abdallah, M. S.; Aboona, B. E.; Adam, J.; Adamczyk, L.; Adams, J. R.; Adkins, J. K.; Agakishiev, G.; Aggarwal, I; Aggarwal, M. M.; Ahammed, Z.; Alekseev, I; Anderson, D. M.; Aparin, A.; Aschenauer, E. C.; Ashraf, M. U.; Atetalla, F. G.; Attri, A.; Averichev, G. S.; Bairathi, V; Baker, W.; Cap, J. G. Ball; Barish, K.; Behera, A.; Bellwied, R.; Bhagat, P.; Bhasin, A.; Bielcik, J.; Bielcikova, J.; Bordyuzhin, I. G.; Brandenburg, J. D.; Brandin, A., V; Bunzarov, I; Butterworth, J.; Cai, X. Z.

来源：Physical Review C - Nuclear Physics, 2021, 104(6): L061901.

DOI：10.1103/PhysRevC.104.L061901

• VORTICITY

Global hyperon polarization, (P) over barH, in Au + Au collisions over a large range of collision energy, root S-NN, was recently measured and successfully reproduced by hydrodynamic and transport models with intense fluid vorticity of the quark-gluon plasma. While naive extrapolation of data trends suggests a large (P) over barH as the collision energy is reduced, the behavior of (P) over barH at small root S-NN < 7.7 GeV is unknown. Operating the STAR experiment in fixed-target mode, we measured the polarization of Lambda hyperons along the direction of global angular momentum in Au + Au collisions at root S-NN = 3 GeV. The observation of substantial polarization of 4.91 +/- 0.81(stat.) +/- 0.15(syst.)% in these collisions may require a reexamination of the viscosity of any fluid created in the collision, of the thermalization timescale of rotational modes, and of hadronic mechanisms to produce global polarization.