Improved quark coalescence model for spin alignment and polarization of hadrons

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 $ϕ$ and $K^{*0}$ (including $\bar{K}^{*0}$) in the static limit: a large positive deviation of $ρ_{00}$ for $ϕ$ mesons from 1/3 may come from the electric part of the vector $ϕ$ field, while a negative deviation of $ρ_{00}$ for $K^{*0}$ may come from the electric part of vorticity tensor fields. Such a negative contribution to $ρ_{00}$ for $K^{*0}$ mesons, in comparison with the same contribution to $ρ_{00}$ for $ϕ$ 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 $ϕ$ ($\mathbf{p}_{b}$ is the relative momentum of two constituent quarks of $K^{*0}$ and $ϕ$). These results should be tested by a detailed and comprehensive simulation of vorticity tensor fields and vector meson fields in heavy ion collisions.