Scaling of Soft QGP Signatures in Relativistic Lead, Xenon, and Oxygen Collisions in EPOS4

The collective expansion and hydrodynamic evolution in heavy-ion collisions is well-established. However, whether femtometer-scale droplets of QGP are produced in small systems at high energies remains a fundamental open question. Analysis of Pb-Pb collisions at √(s_NN) = 5.02 TeV, Xe-Xe at √(s_NN) = 5.44 TeV and O-O collisions at √(s_NN) = 5.36 TeV using EPOS4 is reported to make predictions and postdictions. The results are compared with ALICE data for Pb-Pb and Xe-Xe collisions. Charged particle multiplicity (dN_ch/dη), transverse-momentum (p_T) spectra for pions (π^±), kaons (K^±), and protons (p(p)) are studied. The inclusion of hadronic afterburner, UrQMD (Ultra-relativistic Quantum Molecular Dynamics) is found to be necessary to correctly describe baryon yields. p_T-fluctuations are also studied via normalized p_T correlator, √(⟨⟨ Δp_T,iΔp_T,j⟩⟩)/⟨⟨ p_T⟩⟩. Lastly, anisotropic flow harmonics (v_2{2}, v_3{2}) are computed as a function of p_T and centrality. Since EPOS4 has not been extensively studied for flow observables, this study thereby provides a non-trivial assessment of its collective dynamics. The results are compared with experiment wherever data is available. Taken together, this study provides a unified description of soft observables from Pb-Pb through Xe-Xe down to O-O and offer quantitative guidance on how such collisions may inform of the properties of the QGP.