CMS-PAS-HIN-15-001

CMS-PAS-HIN-15-001
Nuclear modification of $\Upsilon$ states in PbPb
CMS Collaboration
June 2015

Abstract: Yields of $\Upsilon$ (1S), $\Upsilon$ (2S) and $\Upsilon$ (3S) mesons are measured in the CMS experiment via their $\mu^+ \mu^-$ decays, for bottomonium rapidity $\|y\|<$ 2.4, in PbPb and pp collisions at the same energy, $\sqrt{s_{\mathrm{ NN}}} =$ 2.76 TeV. The CMS detector was used to collect integrated luminosity of 166 $\mu$ b $^{-1}$ for PbPb and 5.4 pb $^{-1}$ for pp, corresponding to a similar total number of nucleon-nucleon collisions. Differential cross sections and nuclear modification factors are reported as functions of rapidity and transverse momentum, as well as collision centrality, for the $\Upsilon$ (1S) and the $\Upsilon$ (2S). By comparing to the yield in pp collisions scaled by the number of inelastic nucleon-nucleon collisions, a strong, centrality-dependent suppression is observed in PbPb collisions, by up to a factor of 2 and 10, for the $\Upsilon$ (1S) and the $\Upsilon$ (2S), respectively. No significant dependences are observed as functions of rapidity or transverse momentum. The $\Upsilon$ (3S) was not observed in PbPb collisions, being suppressed by more than 7 at the 95% confidence level.
Links: CDS record (PDF) ; inSPIRE record ; Public twiki page ; CADI line (restricted) ; These preliminary results are superseded in this paper, PLB 770 (2017) 357. The superseded preliminary plots can be found here.

CMS Publications