Speaker
Description
In non-central heavy-ion collisions, large angular momentum is generated, leading to significant vorticity and subsequent spin polarization of particles with finite spin. The global polarization of $\Lambda$ and $\overline{\Lambda}$ hyperons ($P_\Lambda$ and $P_{\overline{\Lambda}}$), measured along the direction of global angular momentum, serves as an effective probe of both vorticity and spin degrees of freedom. $P_\Lambda$ has been measured over a wide range of collision energies. The data from Beam Energy Scan II (BES-II) program at RHIC, including the collider and recent Fixed-Target (FXT), have provided a unique opportunity to study spin degrees of freedom in a wide region of baryon density. In this energy range, $P_\Lambda$ is observed to be sensitive to the equation of state of the nuclear medium.
In this talk, we will present measurements of global $\Lambda$ polarization in Au+Au collisions at $\sqrt{s_{NN}} = 3.0, 3.2, 3.5, 3.9, 4.5, 5.2$, and $6.2$ GeV, along with global $\Lambda$ and $\bar{\Lambda}$ polarization and their differences in Au+Au collisions at $\sqrt{s_{NN}} = 7.7, 9.2, 11.5, 14.6, 17.3$, and $19.6$ GeV from BES-II. The dependence of the measured global polarization on collision energy, centrality, rapidity, and transverse momentum will be discussed.
