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

The STAR collaboration
Phys.Rev.C 98 (2018) 014910, 2018.

Abstract (data abstract)
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. ***Updated polarization values using the new $\alpha_\Lambda=0.732$ published on PDG2020 are also presented in this HEPData entry.***

  • Figure 4

    10.17182/hepdata.99054.v2/t1

    Global polarization of $\Lambda$ and $\bar{\Lambda}$ as a function of the collision energy $\sqrt{s_{_{NN}}}$ for 20-50% centrality Au+Au collisions. Thin...

  • Figure 5

    10.17182/hepdata.99054.v2/t2

    $\Lambda$ ($\bar\Lambda$) polarization as a function of the collision centrality in Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV. Open boxes...

  • Figure 6

    10.17182/hepdata.99054.v2/t3

    Polarization of $\Lambda$ and $\bar\Lambda$ as a function of $p_{T}$ for the $20\%–60\%$ centrality bin in Au+Au collisions at $\sqrt{s_{NN}}...

  • Figure 7

    10.17182/hepdata.99054.v2/t4

    Polarization of $\Lambda$ and $\bar\Lambda$ as a function of $\eta$ for the $20\%–60\%$ centrality bin in Au+Au collisions at $\sqrt{s_{NN}}...

  • Figure 8

    10.17182/hepdata.99054.v2/t5

    Polarization of $\Lambda$ and $\bar\Lambda$ as a function of observed charge asymmetry $A_{ch}$ normalized with its RMS $\sigma_{A_{ch}}$ for the...

  • Figure 4 with New $\alpha$

    10.17182/hepdata.99054.v2/t6

    Global polarization of $\Lambda$ and $\bar{\Lambda}$ using the new $\alpha_\Lambda=0.732$ updated on PDG2020 as a function of the collision energy...

  • Figure 5 with New $\alpha$

    10.17182/hepdata.99054.v2/t7

    $\Lambda$ ($\bar\Lambda$) polarization using the new $\alpha_\Lambda=0.732$ updated on PDG2020 as a function of the collision centrality in Au+Au collisions...

  • Figure 6 with New $\alpha$

    10.17182/hepdata.99054.v2/t8

    Polarization of $\Lambda$ and $\bar\Lambda$ using the new $\alpha_\Lambda=0.732$ updated on PDG2020 as a function of $p_{T}$ for the $20\%–60\%$...

  • Figure 7 with New $\alpha$

    10.17182/hepdata.99054.v2/t9

    Polarization of $\Lambda$ and $\bar\Lambda$ using the new $\alpha_\Lambda=0.732$ updated on PDG2020 as a function of $\eta$ for the $20\%–60\%$...

  • Figure 8 with New $\alpha$

    10.17182/hepdata.99054.v2/t10

    Polarization of $\Lambda$ and $\bar\Lambda$ using the new $\alpha_\Lambda=0.732$ updated on PDG2020 as a function of observed charge asymmetry $A_{ch}$...

Version 2 modifications: In 2020, PDG updated the alpha_lambda value from 0.642 to 0.732. The value, 0.642, was used to calculate the Lambda polarization in the original paper. In this revision the data tables have been updated accordingly using the new value 0.732.

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