Elliptic flow of charm and strange hadrons in high-multiplicity pPb collisions at $\sqrt{s_{_{NN}}} = 8.16~\mathrm{TeV}$

First measurements of the elliptic flow of prompt D$^{0}$ mesons in comparison to $\mathrm{K^0_S}$, $\Lambda$, $\Xi^{-}$, and $\Omega^{-}$ hadrons in pPb collisions at $\sqrt{s_{_{NN}}} = 8.16~\mathrm{TeV}$ are reported. The results are based on data collected by the CMS experiment at the LHC and are presented for particles at midrapidity with transverse momentum up to 8 GeV/c after correcting for the contribution of back-to-back jet correlations. The results are compared to PbPb collision data at $\sqrt{s_{_{NN}}} = 5.02~\mathrm{TeV}$ for $30-50\%$ centrality. A significant elliptic flow ($v_2$) signal is observed for all particles, in very high-multiplicity ($\sim 200$ charged particles) pPb events. When divided by the number of constituent quarks and studied as function of the transverse kinetic energy per quark, the D$^{0}$ $v_2$ values are observed to be significantly smaller than those of light flavor particles, an effect not observed in PbPb collisions. These results show a weaker collective flow associated with charm quarks than with light flavor quarks in high-multiplicity pPb collisions, and may indicate a weaker coupling between heavy quarks and the hypothesised hydrodynamic quark-gluon plasma.