Imaging nuclear shape through anisotropic and radial flow in high-energy heavy-ion collisions

Most atomic nuclei exhibit ellipsoidal shapes characterized by quadrupole deformation β₂ and triaxiality γ, and sometimes even a pear-like octupole deformation β₃. The STAR experiment introduced a new ``imaging-by-smashing'' technique~{STAR:2024eky,Jia:2025wey} to image the nuclear global shape by colliding nuclei at ultra-relativistic speeds and analyzing outgoing debris. Features of nuclear shape manifest in collective observables like anisotropic flow vₙ and radial flow via mean transverse momentum [pT]. We present new measurements of the variances of vₙ ($n=2$, 3, and 4) and [pT], and the covariance of vₙ² with [pT], in collisions of highly deformed ²³⁸U and nearly spherical ¹⁹⁷Au. Ratios of these observables between the two systems effectively suppress common final-state effects, isolating the strong impact of uranium's deformation. By comparing results with state-of-the-art hydrodynamic model calculations, we extract β2U and γU values consistent with those deduced from low-energy nuclear structure measurements. Measurements of v₃ and its correlation with [pT] also provide the first experimental suggestion of a possible octupole deformation for ²³⁸U. These findings provide significant support for using high-energy collisions to explore nuclear shapes on femtosecond timescales, with implications for both nuclear structure and quark-gluon plasma studies.