Speaker
Isaac Upsal
(Ohio State University)
Description
Non-central heavy-ion collisions have large ($\sim 10^{3} \hbar$ in the BES) angular momentum which may be transferred, in part, to the quark-gluon plasma through shear forces that generate a vortical substructure in the hydrodynamic flow field. The vortical nature of the system is expected to polarize emitted hadrons along the direction of system angular momentum. $\Lambda$ and $\overline{\Lambda}$ hyperons, which reveal their polarization through their decay topology, should be polarized similarly.
These same collisions are also characterized by dynamic magnetic fields with magnitudes as large as $10^{14}$ Tesla. A splitting between $\Lambda$ and $\overline{\Lambda}$ polarization may signal a magnetic coupling and provide a quantitative estimate of the field strength at freeze out.
This presentation will discuss the first observation of a global hyperon polarization in non-central Au+Au collisions at the RHIC suite of energies as well as the dependence of this signal on $\Lambda$ kinematic variables ($\phi$, $y$, and $p_T$). The $\phi$ dependence of the signal is of particular interest as one naively expects of larger vorticity in-plane vs. out-of-plane, but the opposite can be found in model calculations. Either way, an in-plane vs. out of plane asymmetry must be related to the details of the fluid properties, including the shear viscosity.
Author
Isaac Upsal
(Ohio State University)
