Evidence of partonic collectivity in OO collisions through the measurement of $ϕ$, K$^0_{\rm S}$, and $Λ$ elliptic flow

Abstract

The first measurement of the elliptic-flow coefficient ($v_{2}$) of $ϕ$, K$^0_{\rm S}$, and $Λ(\overlineΛ)$ hadrons performed in OO collisions at $\sqrt{s_{\mathrm{NN}}}=5.36$ TeV with the ALICE detector is presented as a function of transverse momentum ($p_{\rm T}$) in central and semi-central collisions. For the $ϕ$ meson, in particular, this is the first measurement of the elliptic flow in a small collision system. At low $p_{\rm T}$, a characteristic mass ordering of $v_{2}$ is observed, consistent with collective expansion of the system, in which heavier hadrons are shifted to higher $p_{\rm T}$ by a common velocity field. At intermediate $p_{\rm T}$, above 3 GeV/$c$, a baryon$-$meson splitting with a $10σ$ significance emerges, with the $Λ(\overlineΛ)$ baryon exhibiting larger $v_{2}$ values than mesons, while, despite its mass being close to the mass of the $Λ$, the $ϕ$ follows the K$^{0}_{\rm S}$. The $ϕ$ meson behavior disfavors a purely mass-driven interpretation of the observed patterns and supports the role of hadronization via quark recombination from a collectively flowing partonic medium. These results provide complementary evidence that key signatures of partonic collectivity observed in Pb$-$Pb collisions persist in light nucleus$-$nucleus systems.