Measurement of $\mathrm{\ensuremath{\Upsilon}}(1S)$ Elliptic Flow at Forward Rapidity in Pb-Pb Collisions at $\sqrt{{s}_{NN}}=5.02\text{ }\text{ }\mathrm{TeV}$

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Measurement of $ϒ (1 S)$ Elliptic Flow at Forward Rapidity in Pb-Pb Collisions at $\sqrt{s_{N N}} = 5.02 TeV$

S. Acharya et al. (A Large Ion Collider Experiment Collaboration)

Phys. Rev. Lett. 123, 192301 – Published 6 November 2019

Abstract

The first measurement of the $ϒ (1 S)$ elliptic flow coefficient ( $v_{2}$ ) is performed at forward rapidity ( $2.5 < y < 4$ ) in Pb–Pb collisions at $\sqrt{s_{NN}} = 5.02 TeV$ with the ALICE detector at the LHC. The results are obtained with the scalar product method and are reported as a function of transverse momentum ( $p_{T}$ ) up to $15 GeV / c$ in the 5%–60% centrality interval. The measured $ϒ (1 S) v_{2}$ is consistent with 0 and with the small positive values predicted by transport models within uncertainties. The $v_{2}$ coefficient in $2 < p_{T} < 15 GeV / c$ is lower than that of inclusive $J / ψ$ mesons in the same $p_{T}$ interval by 2.6 standard deviations. These results, combined with earlier suppression measurements, are in agreement with a scenario in which the $ϒ (1 S)$ production in Pb–Pb collisions at LHC energies is dominated by dissociation limited to the early stage of the collision, whereas in the $J / ψ$ case there is substantial experimental evidence of an additional regeneration component.

Received 15 July 2019
Revised 9 September 2019

DOI:https://doi.org/10.1103/PhysRevLett.123.192301

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.