Hayrapetyan, A.Tumasyan, A.Adam, W.Andrejkovic, J. W.Benato, L.Bergauer, T.Chatterjee, S.2026-04-252026-04-2520250031-90071079-7114https://doi.org/10.1103/6ywq-gm61https://hdl.handle.net/11486/8414The polarization of the Lambda and (Lambda) over bar hyperons along the beam direction has been measured in proton-lead (p-Pb) 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 186.0 +/- 6.5 nb(-1). A significant azimuthal dependence of the hyperon polarization, characterized by the second-order Fourier sine coefficient P-z,P-s2, is observed. The P-z,P-s2 values decrease as a function of charged particle multiplicity, but increase with transverse momentum. A hydrodynamic model that describes the observed P-z,P-s2 values in nucleus-nucleus collisions by introducing vorticity effects does not reproduce either the sign or the magnitude of the p-Pb 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.eninfo:eu-repo/semantics/openAccess#BAŞV!Article1351310.1103/6ywq-gm61410767072-s2.0-105018527440Q1WOS:001606770600001Q10000-0002-0662-59040000-0002-2729-62730000-0003-1803-09990009-0008-8227-07550000-0003-1124-84500000-0001-7481-72730000-0001-8893-7401