## Global polarization of $Λ$ hyperons in Au + Au collisions at $\sqrt{s_{_{NN}}}$ =200 GeV

Adam, J. ; Adamczyk, L. ; Adams, J. R. ; Adkins, J. K. ; Agakishiev, G. ; Aggarwal, M. M. ; Ahammed, Z. ; Ajitanand, N. N. ; Alekseev, I. ; Anderson, D. M. ; Aoyama, R. ; Aparin, A. ; Arkhipkin, D. ; Aschenauer, E. C. ; Ashraf, M. U. ; Atetalla, F. ; Attri, A. ; Averichev, G. S. ; Bai, X. ; Bairathi, V. ; Barish, K. ; Bassill, A. J. ; Behera, A. ; Bellwied, R. ; Bhasin, A.

Global polarization of $Λ$ hyperons has been measured to be of the order of a few tenths of a percent in Au+Au collisions at $\sqrt{s_{_{NN}}}$ = 200 GeV, with no significant difference between $Λ$ and $\bar{\Lambda}$. These new results reveal the collision energy dependence of the global polarization together with the results previously observed at $\sqrt{s_{_{NN}}}$ = 7.7 -- 62.4 GeV and indicate noticeable vorticity of the medium created in non-central heavy-ion collisions at the highest RHIC collision energy. The signal is in rough quantitative agreement with the theoretical predictions from a hydrodynamic model and from the AMPT (A Multi-Phase Transport) model. The polarization is larger in more peripheral collisions, and depends weakly on the hyperon's transverse momentum and pseudorapidity $\eta^H$ within $|\eta^H|<1$. An indication of the polarization dependence on the event-by-event charge asymmetry is observed at the 2σ level, suggesting a possible contribution to the polarization from the axial current induced by the initial magnetic field.

Publication Date:
Jul 23 2018
Date Submitted:
Jul 01 2019
ISSN:
2469-9985
Citation:
Physical Review C
98
1
External Resources: