Suppression of Upsilon(1S), Upsilon(2S) and Upsilon(3S) production in PbPb collisions at sqrt(s[NN]) = 2.76 TeV

The CMS collaboration
Phys.Lett.B 770 (2017) 357-379, 2017.

Abstract (data abstract)
CERN-LHC. The production yields of $\Upsilon (1S)$, $\Upsilon (2S)$, and $\Upsilon (3S)$ quarkonium states are measured through their decays into muon pairs in the CMS detector, in PbPb and pp collisions at the centre-of-mass energy per nucleon pair of 2.76 TeV. The data correspond to integrated luminosities of 166 μb−1 and 5.4 pb−1 for PbPb and pp collisions, respectively. Differential production cross sections are reported as functions of $\Upsilon$ rapidity y up to 2.4, and transverse momentum pT up to 20 GeV/c. A strong centrality-dependent suppression is observed in PbPb relative to pp collisions, by factors of up to $\approx 2$ and 8, for the $\Upsilon (1S)$ and $\Upsilon (2S)$ states, respectively. No significant dependence of this suppression is observed as a function of y or pT. The $\Upsilon (3S)$ state is not observed in PbPb collisions, which corresponds to a suppression for the centrality-integrated data by at least a factor of $\approx 7$ at a 95% confidence level. The observed suppression is in agreement with theoretical scenarios modeling the sequential melting of quarkonium states in a quark gluon plasma.

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