Speaker
Description
Recent measurements of $^{16}\rm O$--$^{16}\rm O$ and $^{20}\rm Ne$--$^{20}\rm Ne$ collisions at the CERN Large Hadron Collider provide a new opportunity to investigate the emergence of collective behaviour in hot QCD matter produced in relativistic collisions. The collective expansion of the quark–gluon plasma (QGP) is known to be sensitive to the initial geometry and deformations of the colliding nuclei and can therefore retain their imprints in final-state flow observables, offering a novel probe of intrinsic nuclear structure. Among the proposed structural features of light nuclei with mass number $A=4n$ is $\alpha$-clustering, where nucleons arrange themselves into groups resembling $^{4}\rm He$ nuclei ($\alpha$-clusters). Despite several theoretical and experimental studies exploring the impact of $\alpha$-clusters on collective flow, the degree of cluster compactness remains poorly constrained, particularly in light of the latest experimental data.
Using the hybrid hydrodynamic framework of IP-Glasma+MUSIC+iSS+UrQMD, this work investigates the effect of $\alpha$-cluster compactness on collective flow in OO and Ne--Ne collisions. Rather than treating $\alpha$-clustered and Woods–Saxon nuclear configurations as discrete alternatives, we systematically vary the compactness of $\alpha$-clustered configurations and find that elliptic flow ($v_{2}$) is sensitive to this variation. By comparing our model predictions of $v_{2}$, $v_{2}^{\rm max}$, the corresponding $b^{\rm max}$, and the $v_{2}$(Ne--Ne/OO) and $v_{3}$(Ne--Ne/OO) ratios with the latest Run 3 flow measurements from the ALICE, CMS, and ATLAS Collaborations, we identify the $\alpha$-cluster parametrization that best reproduces the experimental data. A loosely clustered nuclear density profile, approaching the Woods–Saxon limit, is found to have better agreement with the data than a strongly localized $\alpha$-cluster configuration. By placing quantitative constraints on $\alpha$-cluster compactness, this work establishes a connection between high-energy heavy-ion physics, relativistic hydrodynamics, and low-energy nuclear structure, demonstrating that TeV-scale collider observables can provide complementary constraints on intrinsic nuclear geometry.