Origin of the large global spin alignment of phi mesons · revision history

Revision 2

Accepted · cosmetic change · record

Changes against revision 1:

Title
Origin of the large global spin alignment of $\phi$ mesons
Plain · changed
Revision 1: In off-center heavy-ion collisions the produced matter rotates, and spinning particles should line up slightly with the rotation. STAR found that $\phi$ mesons (strange quark plus strange antiquark) line up far more than expected, while K*0 mesons do not.
Revision 2: In off-center heavy-ion collisions the produced matter rotates, and spinning particles should line up slightly with the rotation. STAR found that $\phi$ mesons (strange quark plus strange antiquark) line up far more than expected, while $K*0$ mesons do not.
Precise
STAR measured the spin density-matrix element $\rho_{00}$ of $\phi$ and $K*0$ relative to the reaction plane in $\mathrm{Au}+\mathrm{Au}$ collisions at RHIC (Nature, 2023, doi 10.1038/s41586-022-05557-5): $\rho_{00}(\phi)$ exceeds $1/3$ well beyond the size expected from vorticity and electromagnetic fields, while $\rho_{00}(K*0)$ is consistent with $1/3$. Determine the mechanism. Answer: a model reproducing $\rho_{00}$ for $\phi$ and $K*0$ versus collision energy, centrality and $p_{T}$, with predictions for $J/\psi$ and other vector mesons.
Settled by
Measurements of $\rho_{00}$ for $\phi$, $K*0$ and $J/\psi$ versus energy, rapidity and system size, compared with models that include fluctuating strong-interaction vector fields and hadronization effects.
Kind
phenomenon
Answer type
mechanism
References
(empty)
Literature status
contested
Status note
The 2023 result was attributed by some authors to local fluctuations of strong-force fields, without consensus as of 2026.
Posed since
(empty)

Decisions