Abstract
The elliptic azimuthal anisotropy coefficient (v_{2}) is measured for charm (D^{0}) and strange (K_{S}^{0}, Λ, Ξ^{-}, and Ω^{-}) hadrons, using a data sample of p+Pb collisions collected by the CMS experiment, at a nucleon-nucleon center-of-mass energy of sqrt[s_{NN}]=8.16 TeV. A significant positive v_{2} signal from long-range azimuthal correlations is observed for all particle species in high-multiplicity p+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_{NN}]=5.02 TeV, also presented.
Highlights
AednaetragysamofppleffisoffiffiNffifffiNffipffi 1⁄4þ8P.1b6coTleliVsi.onAs collected by the CMS experiment, at significant positive v2 signal from a nucleonlong-range azimuthal correlations is observed for all particle species in high-multiplicity p þ Pb collisions
The observation of strong collective flow, as inferred from the correlations in azimuthal angle (φ) of particles emitted over a wide pseudorapidity (η) range in relativistic nucleus-nucleus (AA) collisions, has been one of the key signatures suggesting the formation of a strongly interacting quark-gluon plasma (QGP) between the initial impact of the colliding nuclei and final production of particles
The observation of similar correlations in events with high final-state particle multiplicity resulting from proton-proton [15,16,17] and proton-lead (p þ Pb) [18,19,20,21] collisions at the Large Hadron Collider (LHC) has raised the question whether a fluidlike QGP is created in these smaller collision systems [22]
Summary
There has been long-standing interest in the space-time evolution of the multiparticle production process in high energy collisions of hadrons [1]. The elliptic flow results for D mesons in AA collisions measured at RHIC [40] and the LHC [41,42,43] suggest that charm quarks develop strong collective behavior, similar to the bulk production of light flavor particles from the QGP. Observation of D meson v2 in the p þ Pb system, and especially the comparison to the light-flavor and strange particle v2, can impose further constraints on different interpretations related to the origin of the observed long-range collectivity Such measurements can provide key insights into properties of heavy quark interaction and thermalization within a hot QGP medium possibly formed at a significantly reduced system size. Subset of centrality were used and reprocessed using the same reconstruction algorithm as the p þ Pb data
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