Possible octupole deformation of ${}^{208}$Pb and the ultracentral $v_2$ to $v_3$ puzzle

Abstract

Recent measurements have established the sensitivity of ultracentral heavy-ion collisions to the deformation parameters of non-spherical nuclei. In the case of ${}^{129}$Xe collisions, a quadrupole deformation of the nuclear profile led to an enhancement of elliptic flow in the most central collisions. In ${}^{208}$Pb collisions a discrepancy exists in similar centralities, where either elliptic flow is over-predicted or triangular flow is under-predicted by hydrodynamic models; this is known as the $v_2$-to-$v_3$ puzzle in ultracentral collisions. Motivated by low-energy nuclear structure calculations, we consider the possibility that ${}^{208}$Pb nuclei could have a pear shape deformation (octupole), which has the effect of increasing triangular flow in central PbPb collisions. Using the recent data from ALICE and ATLAS, we revisit the $v_2$-to-$v_3$ puzzle in ultracentral collisions, including new constraints from recent measurements of the triangular cumulant ratio $v_3\left\{4\right\}/v_3\left\{2\right\}$ and comparing two different hydrodynamic models. We find that, while an octupole deformation would slightly improve the ratio between $v_2$ and $v_3$, it is at the expense of a significantly worse triangular flow cumulant ratio. In fact, the latter observable prefers no octupole deformation, with ${\beta }_3\lesssim 0.0375$ for ${}^{208}$Pb, and is therefore consistent with the expectation for a doubly-magic nucleus even at top collider energies. The $v_2$-to-$v_3$ puzzle remains a challenge for hydrodynamic models.

11 pages, 11 figures, v2 cosmetic changes to figures

References in corpus (16)

• Elliptic and triangular flow in event-by-event (3+1)D viscous hydrodynamics
• 200 A GeV Au+Au collisions serve a nearly perfect quark-gluon liquid
• Alternative ansatz to wounded nucleon and binary collision scaling in high-energy nuclear collisions
• Transport Coefficients of Bulk Viscous Pressure in the 14-moment approximation
• Particle spectra in Pb-Pb collisions at 2.76 TeV
• Energy density of the Glasma
• Bulk viscosity-driven suppression of shear viscosity effects on the flow harmonics at RHIC
• Measurement of flow harmonics with multi-particle cumulants in Pb+Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV with the ATLAS detector
• Neutron skins and neutron stars
• Multi-particle and charge-dependent azimuthal correlations in heavy-ion collisions at the Relativistic Heavy-Ion Collider
• Constraining the quadrupole deformation of atomic nuclei with relativistic nuclear collisions
• Shape and flow fluctuations in ultra-central Pb+Pb collisions at the LHC
• Extracting the bulk viscosity of the quark-gluon plasma
• Hydrodynamic Predictions for Mixed Harmonic Correlations in 200 GeV Au+Au Collisions
• Glauber Monte Carlo predictions for ultra-relativistic collisions with ${}^{16}\mathrm{O}$
• Ultracentral Collisions of Small and Deformed Systems at RHIC: $UU$, $dAu$, ${}^{9}BeAu$, ${}^{9}Be{}^{9}Be$, ${}^{3}He{}^{3}He$, and ${}^{3}HeAu$ Collisions

Cited by in corpus (16)

• Shape of atomic nuclei in heavy ion collisions
• ${}^{16}{\mathrm{O}}^{16}\mathrm{O}$ at RHIC and the LHC comparing $\alpha$ clustering vs substructure
• Accessing the shape of atomic nuclei with relativistic collisions of isobars
• Scaling approach to nuclear structure in high-energy heavy-ion collisions
• Measures of azimuthal anisotropy in high-energy collisions
• Non-Gaussian transverse momentum fluctuations from impact parameter fluctuations
• Examination of nucleon distribution with Bayesian imaging for isobar collisions
• Hydrodynamic fluctuations and ultra-central flow puzzle in heavy-ion collisions
• Assessing the ultracentral flow puzzle in hydrodynamic modeling of heavy-ion collisions
• Pre-Equilibrium Evolution of Conserved Charges with ICCING Initial Conditions
• Gluonic Hot Spot Initial Conditions in Heavy-Ion Collisions
• Multi-particle correlations, cumulants, and moments sensitive to fluctuations in rare-probe azimuthal anisotropy in heavy ion collisions
• Impact of Multiplicity Fluctuations on Entropy Scaling Across System Size
• Impact parameter dependence of anisotropic flow: Bayesian reconstruction in ultracentral nucleus-nucleus collisions
• Scaling approach to rigid and soft nuclear deformation through flow fluctuations in high-energy nuclear collisions
• Study of octupole deformations in Pb-Pb collisions at 5.02 TeV