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.
Acharyaet al.(ALICE), Phys
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abstract
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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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.
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 component.
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.
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.
citing papers explorer
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Vector-Meson Spin Alignment from Anisotropic Quark or Hadron Coalescence
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.
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Polarization dependence of the $\phi$ meson from finite-temperature QCD sum rules
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.
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Boost-invariant and cylindrically symmetric perfect spin hydrodynamics
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 component.
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Hadron polarization and equation of state at FAIR/RHIC-BES energies
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.
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Boost-invariant perfect Fermi-Dirac spin hydrodynamics
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.