Speaker
Description
Relativistic heavy-ion collisions provide a unique avenue to image nuclear structure by converting initial spatial geometry into the collective expansion of the Quark--Gluon Plasma (QGP). While the quadrupole deformation ($\beta_2$) sits at the center of this paradigm as the primary driver of initial geometry, a complete understanding of nuclear shape requires extending this framework to include triaxiality ($\gamma$), higher-order multipoles such as hexadecapole deformation ($\beta_4$), and the nuclear surface diffuseness ($a$). Connecting these fundamental parameters, however, introduces severe physical challenges: three-dimensional triaxial fluctuations redistribute geometric information unequally across final-state species, higher-order hexadecapole shapes violate conventional multipole scaling rules, and intrinsic shape deformation exhibits a strong degeneracy with the nuclear skin diffuseness. Using event-by-event relativistic hydrodynamic and initial-state simulations, I discuss how the QGP dynamics both compound and resolve these connections. I show that species-dependent differential responses preserve robust maps of quadrupole and triaxial shapes, while higher-order nonlinear mode coupling cleanly isolates intrinsic hexadecapole topologies. Finally, I discuss the shape--diffuseness degeneracy by identifying dynamic correlation strategies that isolate the surface profile independently of deformation and microscopic initial-state uncertainties.
