Probing the octupole deformation of $^{238}$U in high-energy nuclear collisions

Abstract: Some atomic nuclei exhibit ``pear" shapes arising from octupole deformation ($\beta_3$), though direct experimental evidences for such exotic shapes remains scarce. Low-energy model studies suggest $^{238}$U may have a modest octupole deformation arising from collective vibrational degrees of freedom, in addition to a large prolate shape. We investigated the impact of this modest octupole shape on observables involving triangular flow ($v_3$) in high-energy nuclear collisions. Using a hydrodynamic framework, we show $v_3$ and its correlation with mean transverse momentum, $\langle v_3^2 \delta p_{\rm{T}} \rangle$, exhibit strong sensitivity to $\beta_3$. We found that $\langle v_3^2\rangle$ follows a linear increase with $\beta_3^2$, while the characteristic anticorrelation in $\langle v_3^2 \delta p_{\rm{T}} \rangle$ shows a pronounced $\beta_3$-dependent suppression. Our findings demonstrate that the collective-flow-assisted nuclear imaging method in high-energy nuclear collisions, when compared with experimental data, can provide unique quantitative constraints on higher-order deformations.