Sprecher
Beschreibung
Oxygen-oxygen collisions offer a clean testing ground for the onset of collectivity in intermediate-size systems lying between pp and heavy-ion collisions. We study radial flow fluctuations in O+O collisions at $\sqrt{s_{\rm NN}} = 5.36$ TeV using the transverse-momentum-differential observable $v_{0}(p_{\rm T})$, recently measured in Pb+Pb collisions at the LHC. Events are generated with AMPT in its string-melting mode using a Woods-Saxon nuclear profile, and $v_{0}(p_{\rm T})$ is extracted from a two-subevent method within the ALICE central-barrel acceptance ($|\eta| \leq 0.8$). Across centrality classes from 0–5% to 70–80%, $v_{0}(p_{\rm T})$ displays the characteristic radial-flow pattern: negative at low-$p_{\rm T}$, positive and rising at intermediate-$p_{\rm T}$ with an ordered centrality evolution. The $v_{0}(p_{\rm T})$ signal shows no appreciable difference between the forward FT0 and mid-rapidity charged-particle centrality estimators, and persists across subevent pseudorapidity gaps ($\eta_{\rm gap}$) from 0.0 to 0.4, indicating that it is dominated by genuine long-range collective correlations rather than short-range non-flow contributions. For identified hadrons ($\pi^{\pm}, K^{\pm}, p+\overline p$) in most central collisions, $v_{0}(p_{\rm T})$ exhibits a clear mass-ordering at low-$p_{\rm T}$ and a baryon–meson crossing at intermediate-$p_{\rm T}$. Together, these features are consistent with the development of collective radial flow in O+O collisions and establish $v_{0}(p_{\rm T})$ as a robust, non-flow-suppressed probe of the onset of collectivity in small systems.