A1 Journal article (refereed)
Evidence of Spin-Orbital Angular Momentum Interactions in Relativistic Heavy-Ion Collisions (2020)

ALICE Collaboration (2020). Evidence of Spin-Orbital Angular Momentum Interactions in Relativistic Heavy-Ion Collisions. Physical Review Letters, 125 (1), 012301. DOI: 10.1103/PhysRevLett.125.012301

JYU authors or editors

Publication details

All authors or editors: ALICE Collaboration

Journal or series: Physical Review Letters

ISSN: 0031-9007

eISSN: 1079-7114

Publication year: 2020

Volume: 125

Issue number: 1

Article number: 012301

Publisher: American Physical Society

Publication country: United States

Publication language: English

DOI: https://doi.org/10.1103/PhysRevLett.125.012301

Open Access: Open access publication published in a hybrid channel

Publication is parallel published (JYX): https://jyx.jyu.fi/handle/123456789/71211


The first evidence of spin alignment of vector mesons (K*0 and ϕ) in heavy-ion collisions at the Large Hadron Collider (LHC) is reported. The spin density matrix element ρ00 is measured at midrapidity (|y|<0.5) in Pb-Pb collisions at a center-of-mass energy (√sNN) of 2.76 TeV with the ALICE detector. ρ00 values are found to be less than 1/3 (1/3 implies no spin alignment) at low transverse momentum (pT<2  GeV/c) for K*0 and ϕ at a level of 3σ and 2σ, respectively. No significant spin alignment is observed for the K0S meson (spin=0) in Pb-Pb collisions and for the vector mesons in pp collisions. The measured spin alignment is unexpectedly large but qualitatively consistent with the expectation from models which attribute it to a polarization of quarks in the presence of angular momentum in heavy-ion collisions and a subsequent hadronization by the process of recombination.

Keywords: particle physics; spin (quantum mechanics)

Contributing organizations

Ministry reporting: Yes

Preliminary JUFO rating: 3

Last updated on 2021-22-02 at 12:59