Anisotropic flow in fixed-target $^{208}$Pb+$^{20}$Ne collisions as a probe of quark-gluon plasma

TL;DR

This paper predicts anisotropic flow in fixed-target Pb+Ne collisions at the LHCb detector using hydrodynamic models, aiming to probe quark-gluon plasma formation and nuclear shape effects in upcoming experimental data.

Contribution

It provides the first hydrodynamic predictions for anisotropic flow in fixed-target heavy-ion collisions with detailed nuclear shape considerations, guiding future experimental tests.

Findings

Elliptic flow ($v_2$) is significantly enhanced in Pb+Ne due to Ne's deformation.

Large Pb radius broadens the centrality range where flow effects are observed.

Flow measurements can reveal nuclear shape and QGP formation in fixed-target experiments.

Abstract

The System for Measuring Overlap with Gas (SMOG2) at the LHCb detector enables the study of fixed-target ion-ion collisions at relativistic energies ($\sqrt{s_{\rm NN}}\sim100$ GeV in the centre-of-mass). With input from \textit{ab initio} calculations of the structure of $^{16}$O and $^{20}$Ne, we compute 3+1D hydrodynamic predictions for the anisotropic flow of Pb+Ne and Pb+O collisions, to be tested with upcoming LHCb data. This will allow the detailed study of quark-gluon plasma (QGP) formation as well as experimental tests of the predicted nuclear shapes. Elliptic flow ($v_2$) in Pb+Ne collisions is greatly enhanced compared to the Pb+O baseline due to the shape of $^{20}$Ne, which is deformed in a bowling-pin geometry. Owing to the large $^{208}$Pb radius, this effect is seen in a broad centrality range, a unique feature of this collision configuration. Larger elliptic flow further enhances the quadrangular flow ($v_4$) of Pb+Ne collisions via non-linear coupling, and impacts the sign of the kurtosis of the elliptic flow vector distribution ($c_2\{4\}$). Exploiting the shape of $^{20}$Ne proves thus an ideal method to investigate the formation of QGP in fixed-target experiments at LHCb, and demonstrates the power of SMOG2 as a tool to image nuclear ground states.