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Global polarization of $\Lambda$ and $\overline{\Lambda}$ hyperons in Pb-Pb collisions at the LHC

The collaboration
Phys.Rev. C101 (2020) 044611, 2020.

Abstract (data abstract)
The global polarization of the $\Lambda$ and $\overline\Lambda$ hyperons is measured for Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ and $5.02$~TeV recorded with the ALICE at the LHC. The results are reported differentially as a function of collision centrality and hyperon's transverse momentum ($p_{\mathrm{T}}$) for the range of centrality 5-50\%, $0.5 < p_{\mathrm{T}}<5$~GeV/$c$, and rapidity $|y|<0.5$. The hyperon global polarization averaged for Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ and $5.02$~TeV is found to be consistent with zero, $\langle P_{\mathrm{H}}\rangle(\%)\approx 0.01\pm 0.06~(stat.) \pm 0.03~(syst.)$ in the collision centrality range 15-50\%, where the largest signal is expected. The results are compatible with expectations based on an extrapolation from measurements at lower collision energies at RHIC, hydrodynamical model calculations, and empirical estimates based on collision energy dependence of directed flow, all of which predict the global polarization values at LHC energies of the order of $0.01\%$.

• #### R1_SP vs. centrality (LHC10h)

Figure 1

10.17182/hepdata.94265.v1/t1

The correction $R_{\mathrm{SP}}^{(1)}$ for finite resolution of the spectator plane angle $\Psi_{\mathrm{SP}}$ as a function of collision centrality for LHC10h...

• #### R1_SP vs. centrality (LHC11h)

Figure 1

10.17182/hepdata.94265.v1/t2

The correction $R_{\mathrm{SP}}^{(1)}$ for finite resolution of the spectator plane angle $\Psi_{\mathrm{SP}}$ as a function of collision centrality for LHC11h...

• #### R1_SP vs. centrality (LHC15h)

Figure 1

10.17182/hepdata.94265.v1/t3

The correction $R_{\mathrm{SP}}^{(1)}$ for finite resolution of the spectator plane angle $\Psi_{\mathrm{SP}}$ as a function of collision centrality for LHC15h...

• #### P_Lambda vs. centrality (2.76 TeV)

Figure 3

10.17182/hepdata.94265.v1/t4

The $\Lambda$ global polarization as function of centrality for Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$~TeV.

• #### P_AntiLambda vs. centrality (2.76 TeV)

Figure 3

10.17182/hepdata.94265.v1/t5

The $\bar\Lambda$ global polarization as function of centrality for Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$~TeV.

• #### P_Lambda vs. centrality (5.02 TeV)

Figure 3

10.17182/hepdata.94265.v1/t6

The $\Lambda$ global polarization as function of centrality for Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$~TeV.

• #### P_AntiLambda vs. centrality (5.02 TeV)

Figure 3

10.17182/hepdata.94265.v1/t7

The $\bar\Lambda$ global polarization as function of centrality for Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$~TeV.

• #### P_Lambda vs. wide centrality bins (2.76 TeV)

Table 2 and Figure 5

10.17182/hepdata.94265.v1/t8

The $\Lambda$ global polarization as function of centrality for Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$~TeV.

• #### P_AntiLambda vs. wide centrality bins (2.76 TeV)

Table 2 and Figure 5

10.17182/hepdata.94265.v1/t9

The $\bar\Lambda$ global polarization as function of centrality for Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$~TeV.

• #### P_Lambda vs. wide centrality bins (5.02 TeV)

Table 2 and Figure 5

10.17182/hepdata.94265.v1/t10

The $\Lambda$ global polarization as function of centrality for Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$~TeV.

• #### P_AntiLambda vs. wide centrality bins (5.02 TeV)

Table 2 and Figure 5

10.17182/hepdata.94265.v1/t11

The $\bar\Lambda$ global polarization as function of centrality for Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$~TeV.

• #### Average P_H

Table 2

10.17182/hepdata.94265.v1/t12

The average $(\Lambda+\bar\Lambda) \times (2.76+5.02)$ global polarization in Pb-Pb collisions for centrality 15-50%.

• #### P_Lambda vs. pT (2.76TeV, 5-15%)

Figure 4

10.17182/hepdata.94265.v1/t13

The $\Lambda$ global polarization as function of transverse momentum ($p_{\mathrm{T}}$) for 5-15% centrality in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$~TeV.

• #### P_Lambda vs. pT (2.76TeV, 15-50%)

Figure 4

10.17182/hepdata.94265.v1/t14

The $\Lambda$ global polarization as function of transverse momentum ($p_{\mathrm{T}}$) for 15-50% centrality in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$~TeV.

• #### P_AntiLambda vs. pT (2.76TeV, 5-15%)

Figure 4

10.17182/hepdata.94265.v1/t15

The $\bar\Lambda$ global polarization as function of transverse momentum ($p_{\mathrm{T}}$) for 5-15% centrality in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$~TeV.

• #### P_AntiLambda vs. pT (2.76TeV, 15-50%)

Figure 4

10.17182/hepdata.94265.v1/t16

The $\bar\Lambda$ global polarization as function of transverse momentum ($p_{\mathrm{T}}$) for 15-50% centrality in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$~TeV.

• #### P_Lambda vs. pT (5.02TeV, 5-15%)

Figure 4

10.17182/hepdata.94265.v1/t17

The $\Lambda$ global polarization as function of transverse momentum ($p_{\mathrm{T}}$) for 5-15% centrality in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$~TeV.

• #### P_Lambda vs. pT (5.02TeV, 15-50%)

Figure 4

10.17182/hepdata.94265.v1/t18

The $\Lambda$ global polarization as function of transverse momentum ($p_{\mathrm{T}}$) for 15-50% centrality in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$~TeV.

• #### P_AntiLambda vs. pT (5.02TeV, 5-15%)

Figure 4

10.17182/hepdata.94265.v1/t19

The $\bar\Lambda$ global polarization as function of transverse momentum ($p_{\mathrm{T}}$) for 5-15% centrality in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$~TeV.

• #### P_AntiLambda vs. pT (5.02TeV, 15-50%)

Figure 4

10.17182/hepdata.94265.v1/t20

The $\bar\Lambda$ global polarization as function of transverse momentum ($p_{\mathrm{T}}$) for 15-50% centrality in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$~TeV.