Global polarization of ΛLambdaΛ hyperons has been measured to be of the order of a few tenths of a percent in Au+Au collisions at sNNsqrt{s_{_{NN}}}sNN = 200 GeV, with no significant difference between ΛLambdaΛ and Λˉar{Lambda}Λˉ. These new results reveal the collision energy dependence of the global polarization together with the results previously observed at sNNsqrt{s_{_{NN}}}sNN = 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 ηHeta^HηH within ∣ηH∣<1|eta^H|<1∣ηH∣<1. An indication of the polarization dependence on the event-by-event charge asymmetry is observed at the 2σ2sigma2σ level, suggesting a possible contribution to the polarization from the axial current induced by the initial magnetic field.
Global polarization of Lambda hyperons in Au plus Au collisions at root s(NN)=200 GeV
Fazio, S.;
2018-01-01
Abstract
Global polarization of ΛLambdaΛ hyperons has been measured to be of the order of a few tenths of a percent in Au+Au collisions at sNNsqrt{s_{_{NN}}}sNN = 200 GeV, with no significant difference between ΛLambdaΛ and Λˉar{Lambda}Λˉ. These new results reveal the collision energy dependence of the global polarization together with the results previously observed at sNNsqrt{s_{_{NN}}}sNN = 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 ηHeta^HηH within ∣ηH∣<1|eta^H|<1∣ηH∣<1. An indication of the polarization dependence on the event-by-event charge asymmetry is observed at the 2σ2sigma2σ level, suggesting a possible contribution to the polarization from the axial current induced by the initial magnetic field.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.