Observation of (Formula presented) Hyperon Local Polarization in (Formula presented)-Pb Collisions at (Formula presented)

The polarization of the (Formula presented) and (Formula presented) hyperons along the beam direction has been measured in proton-lead ((Formula presented)) collisions at a center-of-mass energy per nucleon pair of 8.16 TeV. The data were obtained with the CMS detector at the LHC and correspond to an integrated luminosity of (Formula presented). A significant azimuthal dependence of the hyperon polarization, characterized by the second-order Fourier sine coefficient (Formula presented), is observed. The (Formula presented) values decrease as a function of charged particle multiplicity, but increase with transverse momentum. A hydrodynamic model that describes the observed (Formula presented) values in nucleus-nucleus collisions by introducing vorticity effects does not reproduce either the sign or the magnitude of the (Formula presented) results. These observations pose a challenge to the current theoretical implementation of spin polarization in heavy ion collisions and offer new insights into the origin of spin polarization in hadronic collisions at LHC energies.