The unexpected uses of a bowling pin: anisotropic flow in fixed-target ^208Pb+^20Ne collisions as a probe of quark-gluon plasma

The System for Measuring Overlap with Gas (SMOG2) at the LHCb detector enables the study of fixed-target ion-ion collisions at relativistic energies (√(s_ NN)∼100 GeV in the centre-of-mass). With input from ab initio calculations of the structure of ^16O and ^20Ne, 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 ^20Ne, which is deformed in a bowling-pin geometry. Owing to the large ^208Pb 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 ^20Ne 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.