Measurement of the (anti-) He elliptic flow in Pb–Pb collisions at

The elliptic flow (${v}_{2}$) of (anti-)$^{3}$He is measured in Pb–Pb collisions at $\sqrt{{s}_{\mathrm{NN}}}=5.02\phantom{\rule{0.25em}{0ex}}\text{TeV}$ in the transverse-momentum (${p}_{T}$) range of 2–6 GeV/c for the centrality classes 0–20%, 20–40%, and 40–60% using the event-plane method. This measurement is compared to that of pions, kaons, and protons at the same center-of-mass energy. A clear mass ordering is observed at low ${p}_{T}$, as expected from relativistic hydrodynamics. The violation of the scaling of ${v}_{2}$ with the number of constituent quarks at low ${p}_{T}$, already observed for identified hadrons and deuterons at LHC energies, is confirmed also for (anti-)$^{3}$He. The elliptic flow of (anti-)$^{3}$He is underestimated by the Blast-Wave model and overestimated by a simple coalescence approach based on nucleon scaling. The elliptic flow of (anti-)$^{3}$He measured in the centrality classes 0–20% and 20–40% is well described by a more sophisticated coalescence model where the phase-space distributions of protons and neutrons are generated using the iEBE-VISHNU hybrid model with AMPT initial conditions.