Elliptic Flow of Heavy Quarkonia in pA Collisions

Abstract

Using the dilute-dense factorization in the Color Glass Condensate framework, we investigate the azimuthal angular correlation between a heavy quarkonium and a charged light hadron in protonnucleus collisions. We extract the second harmonic v2, commonly known as the elliptic flow, with the light hadron as the reference. This particular azimuthal angular correlation between a heavy meson and a light hadron has first been measured at the LHC recently. The experimental results indicate that the elliptic flows for heavy-flavor mesons (J/ψ and D 0 ) are almost as large as those for light hadrons. Our calculation demonstrates that this result can be naturally interpreted as an initial state effect due to the interaction between the incoming partons from the proton and the dense gluons inside the target nucleus. Since the heavy quarkonium v2 exhibits a weak mass dependence according to our calculation, we predict that the heavy quarkonium Υ should have a similar elliptic flow as compared to that of the J/ψ, which can be tested in future measurements.

Particle correlations from the initial state

“…Therefore, in this case both colliding objects can be treated in the CGC 10 Here we refer to gluon production which is the dominant mechanism at small x or high energies. Quarks, obeying Fermi-Dirac statistics and belonging to a non-real colour representation, can give rise to odd harmonics as investigated in [60,77,78]. 11 Besides, the role of the centrality or multiplicity event selection for the breaking of the accidental symmetry and the appearance of odd azimuthal harmonics has been analysed in [79].…”

Unified description of hadron yield ratios from dynamical core-corona initialization

“…One of those data shows sizable azimuthal anisotropy in final hadron distributions [8][9][10][11][12][13][14], which can be interpreted as a result of the hydrodynamic response of the QGP medium to the initial collision geometry [15][16][17][18][19][20][21][22]. Although this has been discussed actively from relativistic hydrodynamics, another interpretation is brought about also by the color glass condensate picture, which gives long-range correlation in rapidity in small colliding systems without invoking the QGP formation [23][24][25][26][27][28][29][30][31][32][33][34][35][36]. Thus the origin of collectivity observed in small colliding system still remains to be understood.…”

Quarkonium: Experimental Overview

“…Transport model calculations that successfully describe the low 2 in Pb+Pb collisions have been applied to +Pb collisions, and do not give a 2 amplitude that is sufficient to match the data, implying that mechanisms beyond final state collectivity may be at play [13]. A different calculation based on the CGC framework gives a significant 2 due to correlations between gluons inside the target nucleus [14], although we note that similar CGC calculations have had mixed results describing light flavor 2 in small systems.…”