Hayrapetyan, A.Tumasyan, A.Adam, W.Andrejkovic, J. W.Benato, L.Bergauer, T.Druzhkin, D.2026-01-102026-01-1020250031-90071079-7114https://doi.org/10.1103/6ywq-gm61https://hdl.handle.net/123456789/12877Petković, Ano/0009-0005-9565-6399; Knight, Charlotte Rose/0009-0008-1167-4816; Robertshaw, Liam/0009-0006-5304-2492; Pfeffer, Emanuel/0009-0009-1748-974X; Menezes De Oliveira, Thales/0009-0009-4729-8354; Castilla-Valdez, Heriberto/0009-0005-9590-9958; Qin, Xuelong/0009-0007-5089-3694The 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/openAccessArticle10.1103/6ywq-gm612-s2.0-105018527440