# Measurement of $\Upsilon(1{\rm S})$ elliptic flow at forward rapidity in Pb-Pb collisions at $\sqrt{s_{\rm{NN}}}=5.02$ TeV

## TL;DR

This paper reports the first measurement of the elliptic flow coefficient ($v_2$) of $Upsilon(1S)$ mesons at forward rapidity in Pb-Pb collisions at 5.02 TeV, showing results consistent with zero and providing insights into quarkonium production mechanisms.

## Contribution

It provides the first measurement of $Upsilon(1S)$ elliptic flow at forward rapidity in heavy-ion collisions, comparing it with J/$psi$ results to understand production dynamics.

## Key findings

- $Upsilon(1S)$ $v_2$ is consistent with zero within uncertainties.
- $v_2$ of $Upsilon(1S)$ is lower than that of J/$psi$ by 2.6 standard deviations.
- Results support a dissociation-dominated production scenario for $Upsilon(1S)$.

## Abstract

The first measurement of the $\Upsilon(1{\rm S})$ elliptic flow coefficient ($v_2$) is performed at forward rapidity (2.5 $<$ $y$ $<$ 4) in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ 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 ($p_{\rm{T}}$) up to 15 GeV/$c$ in the 5-60% centrality interval. The measured $\Upsilon(1{\rm S})$ $v_2$ is consistent with zero and with the small positive values predicted by transport models within uncertainties. The $v_2$ coefficient in 2 $<$ $p_{\rm T}$ $<$ 15 GeV/$c$ is lower than that of inclusive J/$\psi$ mesons in the same $p_{\rm{T}}$ interval by 2.6 standard deviations. These results, combined with earlier suppression measurements, are in agreement with a scenario in which the $\Upsilon$(1S) production in Pb-Pb collisions at LHC energies is dominated by dissociation limited to the early stage of the collision whereas in the J/$\psi$ case there is substantial experimental evidence of an additional regeneration component.