Speaker
Description
While elliptic flow ($v_2$) is a well-established signature of the quark-gluon plasma (QGP) in heavy-ion collisions, its observation in small collision systems remains a topic of active investigation. The LHC experiments first demonstrated the existence of $v_2$ in most central high-multiplicity collisions of p+p/Pb, which was soon complemented by the observation of collective effects in d+Au collisions at RHIC. Measurements of $v_2$ values in p+Au collisions provide further insight into the origin of observed azimuthal anisotropy in small collision systems and allow to determine whether it originates from collective flow or non-flow correlations. Due to superior signal-background ratio neutral pions ($\pi^{0}$) can extend the study of $v_2$ into lower multiplicity and higher transverse momentum ($p_T$) ranges.
This talk will present recent measurements of π⁰ $v_2$ as a function of $p_T$ in various centrality classes in p+Au collisions at 200 GeV. Obtained $\pi^{0}$ $v_2$ values in 0-5% centrality class are consistent with previous $\pi^{\pm}$, $h^{\pm}$ $v_2$ results at RHIC up to $p_T$ ≈ 2.5 GeV/c. This agreement also persists across the 20–40% centrality, where the $\pi^{0}$ $v_2$ measurements align with $h^{\pm}$ data. The consistency of $\pi^{0}$ $v_2$ with $h^{\pm}$ $v_2$ in the 40–60% centrality up to $p_T$ ≈ 4 GeV/c probably indicates a contribution from non-flow effects at higher $p_T$.
The $\pi^{0}$ $v_2$ values measured in 0-5% centrality class, characterized by the highest particle multiplicity, have been scaled with the number of constituent quarks ($n_q$). It was found that normalization of the measured $\pi^{0}$ $v_2$ values leads to agreement between the $\pi^{0}$ $v_2$/$n_q$ values and those for $\pi^{\pm}$ and $p^{\pm}$ within the uncertainties.
The results of the work can be expanded for use in the MPD experiment of the NICA project. The authors acknowledge support from the Ministry of Science and Higher Education of the Russian Federation, state assignment for fundamental research (code FSEG-2025-0009).
