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

CMS Collaboration

doi:10.1103/6ywq-gm61

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

CMS Collaboration

Yerevan Physics Institute
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Vienna University of Technology
University of Antwerp
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Institute for Nuclear Research and Nuclear Energy Bulgarian Academy of Sciences
University of Sofia
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Institute of High Energy Physics, Chinese Academy of Sciences
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China Center of Advanced Science and Technology World Laboratory
China Spallation Neutron Source
State Key Laboratory of Nuclear Physics and Technology
South China Normal University
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Nanjing Normal University
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Universidad de Los Andes, Colombia
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Ruđer Bošković Institute
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University of Cyprus
Charles University
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Universidad San Francisco de Quito
Egyptian Network of High Energy Physics
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British University in Egypt
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National Institute of Chemical Physics and Biophysics, Tallinn
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University of Ioannina
Wigner Research Centre for Physics
Institute of Nuclear Research ATOMKI
Universitatea Babes-Bolyai — Facultatea de Fizica
Eötvös Loránd University
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University College Dublin
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Politecnico di Bari
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ENEA Climate Modeling and Impacts
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Abstract

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.

Original language	English
Article number	132301
Journal	Physical Review Letters
Volume	135
Issue number	13
DOIs	https://doi.org/10.1103/6ywq-gm61
Publication status	Published - 26 Sept 2025

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10.1103/6ywq-gm61

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@article{1a81761288274c6c8d83488246eeaefa,

title = "Observation of (Formula presented) Hyperon Local Polarization in (Formula presented)-Pb Collisions at (Formula presented)",

abstract = "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.",

author = "\{CMS Collaboration\} and A. Hayrapetyan and A. Tumasyan and W. Adam and Andrejkovic, \{J. W.\} and L. Benato and T. Bergauer and S. Chatterjee and K. Damanakis and M. Dragicevic and Hussain, \{P. S.\} and M. Jeitler and N. Krammer and A. Li and D. Liko and I. Mikulec and J. Schieck and R. Sch{\"o}fbeck and D. Schwarz and M. Sonawane and W. Waltenberger and Wulz, \{C. E.\} and T. Janssen and \{Van Laer\}, T. and \{Van Mechelen\}, P. and N. Breugelmans and J. D{\textquoteright}Hondt and S. Dansana and \{De Moor\}, A. and M. Delcourt and F. Heyen and S. Lowette and I. Makarenko and D. M{\"u}ller and S. Tavernier and M. Tytgat and \{Van Onsem\}, \{G. P.\} and \{Van Putte\}, S. and D. Vannerom and B. Bilin and B. Clerbaux and F. Beaudette and A. Cappati and O. Davignon and \{De Wit\}, A. and \{Granier de Cassagnac\}, R. and M. Nguyen and C. Ochando and R. Salerno and A. Zabi and A. Zghiche",

note = "Publisher Copyright: {\textcopyright} 2025 CERN, for the CMS Collaboration.",

year = "2025",

month = sep,

day = "26",

doi = "10.1103/6ywq-gm61",

language = "English",

volume = "135",

journal = "Physical Review Letters",

issn = "0031-9007",

number = "13",

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TY - JOUR

T1 - Observation of (Formula presented) Hyperon Local Polarization in (Formula presented)-Pb Collisions at (Formula presented)

AU - CMS Collaboration

AU - Hayrapetyan, A.

AU - Tumasyan, A.

AU - Adam, W.

AU - Andrejkovic, J. W.

AU - Benato, L.

AU - Bergauer, T.

AU - Chatterjee, S.

AU - Damanakis, K.

AU - Dragicevic, M.

AU - Hussain, P. S.

AU - Jeitler, M.

AU - Krammer, N.

AU - Li, A.

AU - Liko, D.

AU - Mikulec, I.

AU - Schieck, J.

AU - Schöfbeck, R.

AU - Schwarz, D.

AU - Sonawane, M.

AU - Waltenberger, W.

AU - Wulz, C. E.

AU - Janssen, T.

AU - Van Laer, T.

AU - Van Mechelen, P.

AU - Breugelmans, N.

AU - D’Hondt, J.

AU - Dansana, S.

AU - De Moor, A.

AU - Delcourt, M.

AU - Heyen, F.

AU - Lowette, S.

AU - Makarenko, I.

AU - Müller, D.

AU - Tavernier, S.

AU - Tytgat, M.

AU - Van Onsem, G. P.

AU - Van Putte, S.

AU - Vannerom, D.

AU - Bilin, B.

AU - Clerbaux, B.

AU - Beaudette, F.

AU - Cappati, A.

AU - Davignon, O.

AU - De Wit, A.

AU - Granier de Cassagnac, R.

AU - Nguyen, M.

AU - Ochando, C.

AU - Salerno, R.

AU - Zabi, A.

AU - Zghiche, A.

PY - 2025/9/26

Y1 - 2025/9/26

N2 - 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.

AB - 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.

UR - https://www.scopus.com/pages/publications/105018527440

U2 - 10.1103/6ywq-gm61

DO - 10.1103/6ywq-gm61

M3 - Article

C2 - 41076707

AN - SCOPUS:105018527440

SN - 0031-9007

VL - 135

JO - Physical Review Letters

JF - Physical Review Letters

IS - 13

M1 - 132301

ER -

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

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