The elliptic azimuthal anisotropy coefficient ($v_2$) is measured for charm ($D^0$) and strange ($K_S^0$, $\mathrm{\Lambda }$, ${\mathrm{\Xi }}^{-}$, and ${\mathrm{\Omega }}^{-}$) hadrons, using a data sample of $p+\mathrm{Pb}$ collisions collected by the CMS experiment, at a nucleon-nucleon center-of-mass energy of $\sqrt{s_{\mathrm{NN}}}=8.16\mathrm{TeV}$. A significant positive $v_2$ signal from long-range azimuthal correlations is observed for all particle species in high-multiplicity $p+\mathrm{Pb}$ collisions. The measurement represents the first observation of possible long-range collectivity for open heavy flavor hadrons in small systems. The results suggest that charm quarks have a smaller $v_2$ than the lighter quarks, probably reflecting a weaker collective behavior. This effect is not seen in the larger PbPb collision system at $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$, also presented.

• Received 25 April 2018
• Revised 22 July 2018

DOI:https://doi.org/10.1103/PhysRevLett.121.082301

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© 2018 CERN, for the CMS Collaboration