Polarization of $\Lambda$ and $\overline{\Lambda}$ hyperons along the beam direction in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV

The collaboration
Phys.Rev.Lett. 128 (2022) 172005, 2022.

Abstract (data abstract)
The polarization of the $\Lambda$ and $\overline\Lambda$ hyperons along the beam ($z$) direction, $P_{\rm z}$, has been measured in Pb--Pb collisions at $\sqrt{s_{\rm NN}} =$ 5.02 TeV recorded with ALICE at the Large Hadron Collider (LHC). The largest contribution to $P_{\rm z}$ comes from elliptic flow induced vorticity and can be characterized by the second Fourier sine coefficient $P_{\rm z,\,{\rm s2}} = \langle{P_{\rm z}\sin(2\varphi - 2 \Psi_{\rm 2})}\rangle$, where $\varphi$ is the hyperon azimuthal emission angle, and $\Psi_{\rm 2}$ is the elliptic flow plane angle. We report the measurement of $P_{\rm z,\,{\rm s2}}$ for different collision centralities, and in the 30--50\% centrality interval as a function of the hyperon transverse momentum ($p_{\rm T}$) and rapidity ($y_{\rm H}$).

• #### P_z_ANTI-LAMBDA vs. invariant mass (5.02TeV, 30-40%)

Figure 1

10.17182/hepdata.128775.v1/t1

Invariant mass dependence of the $P_{z}$ for $\overline\Lambda$ in the 30-40% centrality class in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV.

• #### P_z vs. centrality (5.02 TeV)

Figure 2

10.17182/hepdata.128775.v1/t2

The average $(\Lambda + \overline\Lambda)$ polarization along beam direction as function of centrality in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV.

• #### P_z vs. pT (5.02TeV, 30-50%)

Figure 3

10.17182/hepdata.128775.v1/t3

The average $(\Lambda + \overline\Lambda)$ polarization along beam direction as function of hyperon transverse momentum ($p_{\mathrm{T}}$) for 30-50% centrality in...

• #### P_z vs. rapidity (5.02TeV, 30-50%)

Figure 4

10.17182/hepdata.128775.v1/t4

The average $(\Lambda + \overline\Lambda)$ polarization along beam direction as function of hyperon rapidity for 30-50% centrality in Pb-Pb collisions...