Elliptic flow fluctuations in central collisions of spherical and deformed nuclei

Abstract

Elliptic flow (v2) fluctuations in central heavy-ion collisions are direct probes of the fluctuating geometry of the quark-gluon plasma, and, as such, are strongly sensitive to any deviation from spherical symmetry in the shape of the colliding nuclei. I investigate the consequences of nuclear deformation for v2 fluctuations, and I assess whether current models of medium geometry are able to predict and capture such effects. Assuming linear hydrodynamic response between v2 and the eccentricity of the medium, ε2, I perform accurate comparisons between model calculations of ε2 fluctuations and STAR data on cumulants of elliptic flow, in central Au+Au and U+U collisions. From these comparisons, I evince that the most distinct signatures of nuclear deformation appear in the non-Gaussianities of v2 fluctuation, and I show, in particular, that the non-Gaussian v2 fluctuations currently observed in central Au+Au collisions are incompatible with model calculations that implement a quadrupole coefficient of order 12% in the 197 Au nuclei. Finally, I make robust predictions for the behavior of higher-order cumulants of v2 in collisions of non-spherical nuclei.

The impact of nuclear deformation on relativistic heavy-ion collisions: assessing consistency in nuclear physics across energy scales

“…From the participant nucleons in AMPT we have a ′ U ≃ 0.0055, while a ′ U ≃ 0.011 in Ref. [13]. However, both calculations return similar ⟨v 2 2 ⟩ U , meaning that the model-dependent estimate of a ′ U is compensated by the hydrodynamic response.…”

“…, with the value of β taken (up to small corrections [12]) from low-energy experiments. Colliding randomly oriented deformed nuclei impacts the initial state of the QGP, enhancing in particular the fluctuations of its ellipticity [13], ε 2 , determined by the transverse positions (r, φ) of the participant nucleons ε 2 = ∑ r 2 e i2φ ∑ r 2 [14]. In hydrodynamics, ε 2 ≠ 0 yields an elliptical imbalance in the pressuregradient forces [15] that drive the expansion of the QGP.…”

Probing triaxial deformation of atomic nuclei in high-energy heavy ion collisions

“…b ′ β 2 3 or b ′ β 2 4 as predicted by Eq. (11). The coefficients b ′ are shown in the right panels.…”

“…Information about nuclear deformation is primarily extracted from spectroscopic measurements and models of reduced transition probability B(En) between low-lying rotational states, which involves nuclear experiments with energy per nucleon less than few 10 MeVs. Recently, the prospects of probing the nuclear deformation at much higher beam energy, energy per nucleon exceeding hundreds of GeVs, by taking advantage of the hydrodynamic flow behavior of large number of produced final-state particles, have been discussed [6][7][8][9][10][11][12][13][14][15][16], several experimental evidences have been observed [17][18][19][20][21].…”

Evidence of quadrupole and octupole deformations in $^{96}$Zr+$^{96}$Zr and $^{96}$Ru+$^{96}$Ru collisions at ultra-relativistic energies

“…Experimental evidences for nuclear deformation are primarily extracted from spectroscopic measurements and models of reduced transition probability between low-lying rotational states, which involves nuclear experiments with energy per nucleon less than few 10 MeVs. Recently, the prospects of probing the nuclear deformation at much higher beam energy, energy per nucleon exceeding hundreds of GeVs, by taking advantage of the responses of hydrodynamic collective flow of the final state particles to the shape and sizes of the initial state, have been discussed [3][4][5][6][7][8][9][10][11][12][13], and several experimental evidences have been observed [14][15][16][17][18].…”