Upsilon suppression in PbPb collisions at the LHC

TL;DR

This paper reports on the measurement of bottomonium suppression in lead-lead collisions at the LHC, providing evidence for sequential melting indicative of quark-gluon plasma formation.

Contribution

First measurement of Y(1S), Y(2S), and Y(3S) suppression in PbPb collisions at 2.76 TeV, demonstrating sequential melting as a signature of quark-gluon plasma.

Findings

Stronger suppression of Y(2S) and Y(3S) compared to Y(1S)

Suppression varies with collision centrality, p_T, and rapidity

Evidence supports quark-gluon plasma formation through sequential melting

Abstract

The Compact Muon Solenoid (CMS) has measured the suppression of the bottomonium states Y(1S), Y(2S), and Y(3S) in PbPb collisions at sqrt(s_NN) = 2.76 TeV relative to pp collisions, scaled by the number of inelastic nucleon-nucleon collisions. CMS observed a stronger suppression for the weaker bound Y(2S) and Y(3S) states than for the ground state Y(1S). Such "sequential melting" has been predicted to be a clear signature for the creation of a quark-gluon plasma. The suppression of the Y(1S) and Y(2S) has been measured as a function of collision centrality for Y in the rapidity interval |y| < 2.4 and with transverse momentum (p_T) down to 0. Furthermore, the p_T and rapidity dependence of the Y(1S) suppression are presented.