Speaker
Summary
In non-central relativistic heavy ion collisions, the created matter possesses a large initial orbital angular momentum. Particles produced in the collisions could be polarized globally in the direction of the orbital angular momentum due to spin-orbit coupling. The measurement of vector mesons $K^{*}$ and $\phi$ can provide information of the large vorticity of the hot, dense medium created in non-central heavy-ion collisions. Due to short lifetime of $K^{*}$ which is comparable to the time between chemical freeze-out and kinetic freeze-out, the reconstructed $K^{*}$ suffers from the rescattering effect ( A $K^{*}$ can not be reconstructed experimentally via the invariant mass method if the $K^{*}$ decays in the medium and one or more daughters is scattered in the medium). Because of the anisotropy of the medium in coordination space, the rescattering effect on $K^{*}$ could depend on cos $\theta^{*}$ thus result in non-uniform cos $\theta^{*}$ distribution for reconstructed $K^{*}$. It could be a very important background for the study of global polarization via the $K^{*}$ spin alignment measurements in non-central heavy-ion collisions.
In this talk, we will present the study of measurement of $K^{*}$ spin alignment in heavy-ion collisions using the UrQMD model. We use the history file to identify $K^{*}$ decays and select the reconstructable $K^{*}$. The cos $\theta^{*}$ distribution is studied and the spin alignment parameter $\rho_{00}$ is exacted and plot against transverse moment and centrality.
