Exploiting Ne²⁰ Isotopes for Precision Characterizations of Collectivity in Small Systems

Whether or not femto-scale droplets of quark-gluon plasma (QGP) are formed in so-called small systems at high-energy colliders is a pressing question in the phenomenology of the strong interaction. For proton-proton or proton-nucleus collisions the answer is inconclusive due to the large theoretical uncertainties plaguing the description of these processes. While upcoming data on collisions of O¹⁶ nuclei may mitigate these uncertainties in the near future, here we demonstrate the unique possibilities offered by complementing O¹⁶ + O¹⁶ data with collisions of Ne²⁰ ions. We couple both nuclear lattice effective field theory (NLEFT) and projected generator coordinate method (PGCM) ab initio descriptions of the structure of Ne²⁰ and O¹⁶ to hydrodynamic simulations of O¹⁶ + O¹⁶ and Ne²⁰ + Ne²⁰ collisions at high energy. We isolate the imprints of the bowling-pin shape of Ne²⁰ on the collective flow of hadrons, which can be used to perform quantitative tests of the hydrodynamic QGP paradigm. In particular, we predict that the elliptic flow of Ne²⁰ + Ne²⁰ collisions is enhanced by as much as 1.174(8)_stat(31)_syst for NLEFT and 1.139(6)_stat(39)_syst for PGCM relative to O¹⁶ + O¹⁶ collisions for the 1% most central events. At the same time, theoretical uncertainties largely cancel when studying relative variations of observables between two systems. This demonstrates a method based on experiments with two light-ion species for precision characterizations of the collective dynamics and its emergence in a small system.