Measurement of Υ(1S) elliptic flow at forward rapidity in Pb-Pb collisions at √sNN=5.02 TeV

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 √ 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.