Suppression of $\Upsilon$(1S) at forward rapidity in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV

TL;DR

This paper reports a significant suppression of $
S$ bottomonium production at forward rapidity in Pb-Pb collisions at 2.76 TeV, indicating strong quark-gluon plasma effects, with results challenging existing models.

Contribution

First measurement of $
S$ suppression at forward rapidity in Pb-Pb collisions at LHC energies, revealing increased suppression compared to mid-rapidity and challenging current theoretical models.

Findings

$
S$ suppression factor of 0.30 in central collisions

Suppression increases with collision centrality

Models underestimate the observed suppression and do not match rapidity dependence

Abstract

We report on the measurement of the inclusive $\Upsilon$(1S) production in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV carried out at forward rapidity ($2.5<y<4$) and down to zero transverse momentum using its $\mu^{+}\mu^{-}$ decay channel with the ALICE detector at the Large Hadron Collider. A strong suppression of the inclusive $\Upsilon$(1S) yield is observed with respect to pp collisions scaled by the number of independent nucleon-nucleon collisions. The nuclear modification factor, for events in the 0-90$\%$ centrality range, amounts to $0.30\pm0.05{\rm (stat)}\pm0.04{\rm (syst)}$. The observed $\Upsilon$(1S) suppression increases with the centrality of the collision and is more pronounced than in corresponding mid-rapidity measurements. Our results are compared with model calculations, which are found to underestimate the measured suppression and fail to reproduce its rapidity dependence.