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

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

STAR

Collaboration

May 11, 2018

11 pages

Published in:

Phys.Rev.C 98 (2018) 014910

Published: Jul 23, 2018

e-Print:

1805.04400 [nucl-ex]

DOI:

10.1103/PhysRevC.98.014910

Experiments:

BNL-RHIC-STAR

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Abstract: (arXiv)

Global polarization of

\Lambda

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

\Lambda

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

2\sigma

level, suggesting a possible contribution to the polarization from the axial current induced by the initial magnetic field.

Note:

11 pages, 8 figures, Accepted for publication in Phys. Rev. C

25.75.-q
25.75.Ld
Lambda: polarization
polarization: dependence
model: hydrodynamics
charge: asymmetry
current: induced
current: axial
heavy ion: scattering
hyperon

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