Elliptic flow fluctuations in central collisions of spherical and deformed nuclei
Résumé
Elliptic flow ($v_2$) 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 $v_2$ fluctuations, and I assess whether current models of medium geometry are able to predict and capture such effects. Assuming linear hydrodynamic response between $v_2$ and the eccentricity of the medium, ɛ$_2$, I perform accurate comparisons between model calculations of ɛ$_2$ 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 $v_2$ fluctuation, and I show, in particular, that the non-Gaussian $v_2$ 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 $v_2$ in collisions of nonspherical nuclei.
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