Observation of prompt J/$\psi$ meson elliptic flow in high-multiplicity pPb collisions at $\sqrt{s_{\mathrm{N}\mathrm{N}}}=$ 8.16 TeV

A measurement of the elliptic flow ($v_2$) of prompt J/$\psi$ mesons in high-multiplicity pPb collisions is reported using data collected by the CMS experiment at a nucleon-nucleon center-of-mass energy $\sqrt{s_{\mathrm{N}\mathrm{N}}}=$ 8.16 TeV. Prompt J/$\psi$ mesons decaying into two muons are reconstructed in the rapidity region in the nucleon-nucleon center-of-mass frame ($y_{\mathrm{c}\mathrm{m}}$), corresponding to either $-$2.86 $<y_{\mathrm{c}\mathrm{m}}<$ $-$1.86 or 0.94 $<y_{\mathrm{c}\mathrm{m}}<$ 1.94. The average $v_2$ result from the two rapidity ranges is reported over the transverse momentum (p${}_{\mathrm{T}}$) range from 0.2 to 10 GeV. Positive $v_2$ values are observed for the prompt J/$\psi$ meson, as extracted from long-range two-particle correlations with charged hadrons, for 2 $<p_{\mathrm{T}}<$ 8 GeV. The prompt J/$\psi$ results are compared with previous CMS measurements of elliptic flow for open charm mesons (D${}^0$) and strange hadrons. From these measurements, constraints can be obtained on the collective dynamics of charm quarks produced in high-multiplicity events arising from small systems.