J/ψ elliptic and triangular flow in Pb-Pb collisions at $$ \sqrt{s_{\mathrm{NN}}} $$ = 5.02 TeV

Abstract

The inclusive J/ψ elliptic (v2) and triangular (v3) flow coefficients measured at forward rapidity (2.5 < y < 4) and the v2 measured at midrapidity (|y| < 0.9) in Pb-Pb collisions at $$ \sqrt{s_{\mathrm{NN}}} $$ s NN = 5.02 TeV using the ALICE detector at the LHC are reported. The entire Pb-Pb data sample collected during Run 2 is employed, amounting to an integrated luminosity of 750 μb−1 at forward rapidity and 93 μb−1 at midrapidity. The results are obtained using the scalar product method and are reported as a function of transverse momentum pT and collision centrality. At midrapidity, the J/ψ v2 is in agreement with the forward rapidity measurement. The centrality averaged results indicate a positive J/ψ v3 with a significance of more than 5σ at forward rapidity in the pT range 2 < pT< 5 GeV/c. The forward rapidity v2, v3, and v3/v2 results at low and intermediate pT (pT ≲ 8 GeV/c) exhibit a mass hierarchy when compared to pions and D mesons, while converging into a species-independent curve at higher pT. At low and intermediate pT, the results could be interpreted in terms of a later thermalization of charm quarks compared to light quarks, while at high pT, path-length dependent effects seem to dominate. The J/ψ v2 measurements are further compared to a microscopic transport model calculation. Using a simplified extension of the quark scaling approach involving both light and charm quark flow components, it is shown that the D-meson vn measurements can be described based on those for charged pions and J/ψ flow.

Heavy Ions, Experimental Overview

“…The differential studies vs p T show an increase of the R AA with decreasing p T , which is well described by theoretical transport models and the statistical hadronisation model that include the regeneration mechanism that dominates at low p T . The observed strong sign of collective effects of J/ψ mesons [40], including also the observed positive v 2 coefficient with a significance of 2.5σ at midrapidity, confirms the regeneration scenario. On the other hand, the suppression mechanism dominates for the bottomonium family as observed by an increasing suppression of Υ(1S), Υ(2S), and Υ(3S) in measurements by the ALICE, ATLAS, CMS and STAR collaborations [41][42][43][44], see e.g.…”

Highlights from the ALICE collaboration

“…In all cases, 2 has been shown to exhibit mass ordering at low momenta, which is expected from hydrodynamic models [5]. Moreover, the 2 of hadrons containing heavyflavour quarks has also been measured and has been observed to be non-zero for D mesons, J/ and even beauty decay electrons [6,7]. Heavier states such as the Υ(1S), however, exhibit 2 consistent with zero within uncertainties in the measured momentum range [8], which indicates that either they do not participate in the collective motion or they do so only outside of the measured range due to their very large masses.…”

Open heavy-flavour production from small to large collision systems with ALICE at the LHC

“…Open heavy-flavour production with ALICE Luuk Vermunt Fig. 3 for several particle species [12][13][14][15]. The elliptic flow is sensitive to the degree of thermalisation of the heavy quarks at low p T , where at high p T it provides additional information on the path-length dependence of the in-medium parton energy loss.…”