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Evidence of spin-orbital angular momentum interactions in relativistic heavy-ion collisions

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arxiv 1910.14408 v2 pith:Q3USREDK submitted 2019-10-31 nucl-ex hep-ex

Evidence of spin-orbital angular momentum interactions in relativistic heavy-ion collisions

classification nucl-ex hep-ex
keywords collisionsspinalignmentheavy-ionmomentumangularevidencelarge
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved
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The first evidence of spin alignment of vector mesons ($K^{*0}$ and $\phi$) in heavy-ion collisions at the Large Hadron Collider (LHC) is reported. The spin density matrix element $\rho_{00}$ is measured at midrapidity ($|y| <$ 0.5) in Pb-Pb collisions at a center-of-mass energy ($\sqrt{s_{\rm NN}}$) of 2.76 TeV with the ALICE detector. $\rho_{00}$ values are found to be less than 1/3 (1/3 implies no spin alignment) at low transverse momentum ($p_{\rm T} <$ 2 GeV/$c$) for $K^{*0}$ and $\phi$ at a level of 3$\sigma$ and 2$\sigma$, respectively. No significant spin alignment is observed for the $K^0_S$ 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.

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Forward citations

Cited by 5 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. Vector-Meson Spin Alignment from Anisotropic Quark or Hadron Coalescence

    hep-ph 2026-07 conditional novelty 6.0

    Anisotropic quark or hadron coalescence in heavy-ion collisions generates vector-meson spin alignment whose sign distinguishes bare-vector from spin-orbit-coupled production vertices.

  2. Polarization dependence of the $\phi$ meson from finite-temperature QCD sum rules

    hep-ph 2026-05 unverdicted novelty 5.0

    Finite-temperature QCD sum rules predict momentum-dependent mass increases and growing transverse-longitudinal splitting for the phi meson, driven primarily by dimension-four spin-dependent thermal condensates.

  3. Boost-invariant and cylindrically symmetric perfect spin hydrodynamics

    hep-ph 2026-05 unverdicted novelty 5.0

    In boost-invariant cylindrical spin hydrodynamics, azimuthal-longitudinal coupling in the spin tensor produces nonzero total polarization only via the longitudinal magnetic component coupled to the azimuthal electric ...

  4. Hadron polarization and equation of state at FAIR/RHIC-BES energies

    nucl-th 2026-06 unverdicted novelty 4.0

    Lambda polarization in low-energy heavy-ion collisions depends on the equation of state in UrQMD simulations and arises from shear in the baryon current due to stopping.

  5. Boost-invariant perfect Fermi-Dirac spin hydrodynamics

    hep-ph 2026-04 unverdicted novelty 4.0

    Fermi-Dirac statistics in boost-invariant perfect spin hydrodynamics produce evolution differences about one order of magnitude smaller than spin-feedback corrections, with special functions conveniently parametrized.