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

TL;DR

This paper reports the first observation of elliptic flow for charm and strange hadrons in high-multiplicity pPb collisions at 8.16 TeV, indicating possible collective behavior of heavy quarks in small systems.

Contribution

It provides the first measurement of elliptic flow for open heavy flavor hadrons in small collision systems, revealing differences in collective behavior between charm and lighter quarks.

Findings

Significant positive $v_2$ observed for all particle species in high-multiplicity pPb collisions.

Charm quarks exhibit smaller $v_2$ than lighter quarks, indicating weaker collectivity.

No similar effect observed in PbPb collisions at 5.02 TeV.

Abstract

The elliptic azimuthal anisotropy coefficient ($v_2$) is measured for charm (D$^0$) and strange (K$_\mathrm{S}^0$, $\Lambda$, $\Xi^-$, and $\Omega^-$) hadrons, using a data sample of pPb collisions collected by the CMS experiment, at a nucleon-nucleon center-of-mass energy $\sqrt{s_{_\mathrm{NN}}} =$ 8.16 TeV. A significant positive $v_2$ signal from long-range azimuthal correlations is observed for all particle species in high-multiplicity pPb 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 TeV, also presented.