New Insights into Global Spin Alignment of Vector Mesons Using Relativistic Heavy-Ion Collisions from STAR

Abstract

In these proceedings, we present new measurements from STAR of the global spin alignment($\rho_{00}$) of $\phi$ mesons in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}$ = 19.6, 14.6 GeV using BES-II data and of $J/\psi$ mesons in isobar collisions ${ }_{44}^{96} \mathrm{Ru}+{ }_{44}^{96} \mathrm{Ru}$ and ${ }_{40}^{96} \mathrm{Zr}+{ }_{40}^{96} \mathrm{Zr}$ at $\sqrt{s_{\mathrm{NN}}}$ = 200 GeV. The energy-dependent spin alignment for $\phi$ mesons from BES-II data is consistent with that published from BES-I and showcases a significant improvement in precision. We performed a new measurement assessing the rapidity dependence of $\phi$ meson $\rho_{00}$, and our findings are consistent with theoretical predictions. The global spin alignment of $J/\psi$ mesons with respect to first order event plane aligns with a value of $1/3$ within the statistical error. Additionally, we discuss the procedure of measuring the global spin alignment of $\rho^0$ mesons at RHIC and provide the projection for errors.