Eur. Phys. J. A (2009) 39: 1-4
https://doi.org/10.1140/epja/i2008-10700-9

Letter

Negative elliptic flow of J/ψ’s: A qualitative signature for charm collectivity at RHIC

Institut für Theoretische Physik, Johann Wolfgang Goethe-Universität, Max-von-Laue-Str. 1, 60438, Frankfurt am Main, Germany

^* e-mail: krieg@th.physik.uni-frankfurt.de

Received: 21 August 2008
Revised: 9 December 2008
Published online: 22 December 2008

Abstract

We discuss one of the most prominent features of the very recent preliminary elliptic flow data of J/ψ-mesons from the PHENIX Collaboration (PHENIX Collaboration (C. Silvestre), arXiv:0806.0475 [nucl-ex]). Even within the rather large error bars of the measured data a negative elliptic flow parameter (v₂) for J/ψ in the range of p _T = 0.5-2.5 GeV/c is visible. We argue that this negative elliptic flow at intermediate p_T is a clear and qualitative signature for the collectivity of charm quarks produced in nucleus-nucleus reactions at RHIC. Within a parton recombination approach we show that a negative elliptic flow puts a lower limit on the collective transverse velocity of heavy quarks. The numerical value of the transverse flow velocity for charm quarks that is necessary to reproduce the data is (charm) ∼ 0.55-0.6c and therefore compatible with the flow of light quarks.