Spin alignment of vector mesons induced by local spin density fluctuations

We propose a novel mechanism that the spin alignment of vector meson ϕ and K * 0 in most central heavy ion collisions is induced by intrinsic quantum chromo dynamics (QCD) without external vortical/magnetic fields. The local spin density fluctuation of quarks due to the axial-vector and tensor interactions between quarks can induce the spin alignments of vector meson. It is found that axial-vector interaction results in ρ 00 < 1 / 3 for the spin alignment of ϕ meson, while tensor interaction results in ρ 00 > 1 / 3 . We argue that the spin alignment of K * 0 due to the spin density fluctuation from flavor-mixing would be a signature or hint of instanton. Published by the American Physical Society 2024