The polarization of the Λ and Λ[over ¯] 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,s2}, is observed. The P_{z,s2} values decrease as a function of charged particle multiplicity, but increase with transverse momentum. A hydrodynamic model that describes the observed P_{z,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.

Hayrapetyan, A., Tumasyan, A., Adam, W., Andrejkovic, J., Benato, L., Bergauer, T., et al. (2025). Observation of Λ Hyperon Local Polarization in p-Pb Collisions at sqrt[s_{NN}]=8.16  TeV. PHYSICAL REVIEW LETTERS, 135(13) [10.1103/6ywq-gm61].

Observation of Λ Hyperon Local Polarization in p-Pb Collisions at sqrt[s_{NN}]=8.16  TeV

Xiao J.;Brivio F.;Cetorelli F.;De Guio F.;Dinardo M. E.;Gerosa R.;Ghezzi A.;Govoni P.;Guzzi L.;Lucchini M. T.;Malberti M.;Moroni L.;Paganoni M.;Palluotto S.;Perego A.;Pinolini B. S.;Pizzati G.;Ragazzi S.;Tabarelli de Fatis T.;
2025

Abstract

The polarization of the Λ and Λ[over ¯] 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,s2}, is observed. The P_{z,s2} values decrease as a function of charged particle multiplicity, but increase with transverse momentum. A hydrodynamic model that describes the observed P_{z,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.
Articolo in rivista - Articolo scientifico
article; polarization
English
23-set-2025
2025
135
13
132301
none
Hayrapetyan, A., Tumasyan, A., Adam, W., Andrejkovic, J., Benato, L., Bergauer, T., et al. (2025). Observation of Λ Hyperon Local Polarization in p-Pb Collisions at sqrt[s_{NN}]=8.16  TeV. PHYSICAL REVIEW LETTERS, 135(13) [10.1103/6ywq-gm61].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/575288
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