Measurements of Upsilon meson suppression in heavy ion collisions with the CMS experiment at the LHC

Measurements of Upsilon suppression in ultra relativistic heavy ion collisions are key to understanding the hot and deconfined phase of matter called Quark-Gluon Plasma (QGP). The cross section of Upsilon states Y(nS) are measured in proton-proton collisions and in lead-lead collisions at the centre-of-mass energy of 2.76 TeV per nucleon pair. Individual states are measured through their dimuon decay channel using the Compact Muon Solenoid (CMS) at CERN. The cross sections measured in pp and PbPb are compared thanks to the nuclear modification factor, $R_{AA}$. This observable is computed for Upsilon(1S) and Upsilon(2S) in several bins of transverse momentum,rapidity and centrality of the collision. An upper limit on the production of Upsilon(3S) in PbPb is estimated. These measurements exhibit a clear and ordered suppression pattern, consistent with the hypothesis of sequential melting of quarkonia in the QGP. The measured Upsilon(1S) and Upsilon(2S) suppressions are observed to be independent of transverse momentum and rapidity. Comparisons with available phenomenological models are presented, however fail to reproduce the full set of observations. This novel measurement thus provides new constraints on the modeling of heavy quark deconfinement.