Global and local polarization of $\Lambda$ ($\bar{\Lambda }$) hyperons in Pb--Pb collisions in ALICE at the LHC

Abstract

The global polarization of the $\Lambda$ and $\bar{\Lambda }$ hyperons ($P_{\mathrm{H}}$) has been measured in Pb--Pb collisions at $\sNN=$ 2.76 TeV and 5.02 TeV in ALICE at the Large Hadron Collider (LHC). The hyperon global polarization is found to be consistent with zero at both collision energies. The local polarization of the $\Lambda$ and $\bar{\Lambda }$ hyperons along the beam ($z$) direction, $P_{\mathrm{z}}$, has also been measured in Pb--Pb collisions at $\sNN=5.02$ TeV. The $P_{\mathrm{z}}$, measured as a function of the hyperon emission angle relative to the second harmonic symmetry plane, exhibits a second harmonic sine modulation, as expected due to elliptic flow. The measurements of global and local hyperon polarization are reported for different collision centralities and as a function of transverse momentum in semicentral collisions. These results show the first experimental evidence of a non-zero hyperon $P_{\mathrm{z}}$ in Pb--Pb collisions at the LHC.

arXiv commentPresented at SQM 2021 - https://indico.cern.ch/event/985652/contributions/4305110/

References in corpus (12)

• Methods for analyzing anisotropic flow in relativistic nuclear collisions
• Global $\Lambda$ hyperon polarization in nuclear collisions: evidence for the most vortical fluid
• Properties of hot and dense matter from relativistic heavy ion collisions
• Polarization probes of vorticity in heavy ion collisions
• A study of vorticity formation in high energy nuclear collisions
• Collective longitudinal polarization in relativistic heavy-ion collisions at very high energy
• Polarization and Entanglement in Baryon-Antibaryon Pair Production in Electron-Positron Annihilation
• Probing vorticity structure in heavy-ion collisions by local $\Lambda$ polarization
• Vorticity and particle polarization in heavy ion collisions (experimental perspective)
• Exact equilibrium distributions in statistical quantum field theory with rotation and acceleration: scalar field
• The Generation of Vorticity in Cosmological N-body Simulations
• Neutrino-deuteron scattering: Uncertainty quantification and new $L_{1,A}$ constraints