Speaker
Description
In non-central heavy-ion collisions (HIC), the large initial angular momentum can induce a non-vanishing polarization for hadrons with non-zero spin. The global spin alignment of vector mesons, quantified by the $00^{th}$ element of spin density matrix ($\rho_{00}$), can offer information on the spin-orbital interactions of the QCD medium. Surprisingly large signal of vector meson $\rho_{00}$ compared to hyperon spin polarization poses challenges to the conventional theoretical understanding of polarization in HIC. Preliminary observations from Beam Energy Scan (BES-I) of large deviations of $\rho_{00}$ from 1/3 for $\phi$ mesons can only be explained by introducing the vector meson strong force fields.
In this talk, we will present transverse momentum and collision centrality dependence of $\phi$, $K^{*0}$, $\overline{K^{*0}}$, $K^{*+}$, and $K^{*-}$ vector mesons using recent high statistics Beam Energy Scan (BES-II) data of Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 7.7 - 27 GeV, and isobar collisions (Zr+Zr and Ru+Ru) at $\sqrt{s_{\rm NN}}$ = 200 GeV. The BES-II data will provide unprecedented precision in $\rho_{00}$ at these energies. Comparison of $\rho_{00}$ between Au+Au and isobar species can provide information on the system size dependence of $\rho_{00}$. Moreover, since the magnetic moment of charged and neutral $K^{*}$ differ by a factor of seven, the comparison of their $\rho_{00}$ may serve as a new probe for the initial strong magnetic field in HIC.
