Improved quark coalescence model for spin alignment and polarization of hadrons

TL;DR

This paper introduces an improved quark coalescence model that explains the spin alignment and polarization of hadrons, linking these phenomena to vector meson fields and vorticity tensor fields in heavy ion collisions.

Contribution

It presents a novel quark coalescence model incorporating phase space dependence and spin density matrices, providing new insights into hadron spin alignment mechanisms.

Findings

Large positive deviation of ρ₀₀ for φ mesons from 1/3 explained by vector φ field.

Negative deviation of ρ₀₀ for K*⁰ mesons linked to vorticity tensor fields.

Amplification of effects due to mass ratio and wave function momentum ratios.

Abstract

We propose an improved quark coalescence model for spin alignment of vector mesons and polarization of baryons by spin density matrix with phase space dependence. The spin density matrix is defined through Wigner functions. Within the model we propose an understanding of spin alignments of vector mesons $\phi$ and $K^{*0}$ (including $\bar{K}^{*0}$) in the static limit: a large positive deviation of $\rho_{00}$ for $\phi$ mesons from 1/3 may come from the electric part of the vector $\phi$ field, while a negative deviation of $\rho_{00}$ for $K^{*0}$ may come from the electric part of vorticity tensor fields. Such a negative contribution to $\rho_{00}$ for $K^{*0}$ mesons, in comparison with the same contribution to $\rho_{00}$ for $\phi$ mesons which is less important, is amplified by a factor of the mass ratio of strange to light quark times the ratio of $\left\langle \mathbf{p}_{b}^{2}\right\rangle $ on the wave function of $K^{*0}$ to $\phi$ ($\mathbf{p}_{b}$ is the relative momentum of two constituent quarks of $K^{*0}$ and $\phi$). These results should be tested by a detailed and comprehensive simulation of vorticity tensor fields and vector meson fields in heavy ion collisions.