Relativistic heavy ion collisions provide a unique opportunity to probe the nuclear structure by taking an instantaneous snapshot of the colliding nuclei and converting it into momentum anisotropies of final emitted hadrons. A long-standing puzzle of too large a ratio of the elliptical-to-triangular ($v_{ 2}$-to-$v_{ 3}$) anisotropies in ultracentral $^{ 208}$Pb+$^{ 208}$Pb collisions at the Large Hadron Collider(LHC) cannot be solved simply by hydrodynamic simulations with initial conditions containing the spherical or certain deformed shape of $^{ 208}$Pb. In this Letter, using the iEBE-VISHNU relativistic viscous hydrodynamic hybrid model simulations with the Trento initial condition, we show that a dynamic octupole deformation--a shape-breathing of $^{ 208}$Pb --could potentially solve the $v_{ 2}$-to-$v_{ 3}$ puzzle and simultaneously describe the $v_3\{ 4\}$ data measured in experiment. Our results highlight the unique capability of capturing transient collective properties of nuclei on yoctosecond ($10^{ -24}$~s) timescales, unfeasible with low-energy nuclear reactions.
Categories: nucl-th nucl-ex