Indications of Suppression of Excited Upsilon States in Pb-Pb Collisions at root(s)NN=2.76 TeV

Abstract

A comparison of the relative yields of Υ resonances in the μ+μ− decay channel in Pb-Pb and pp collisions at a center-of-mass energy per nucleon pair of 2.76 TeV is performed with data collected with the CMS detector at the LHC. Using muons of transverse momentum above 4 GeV/c and pseudorapidity below 2.4, the double ratio of the Υ(2S) and Υ(3S) excited states to the Υ(1S) ground state in Pb-Pb and pp collisions, [Υ(2S+3S)/Υ(1S)]Pb−Pb/[Υ(2S+3S)/Υ(1S)]pp, is found to be 0.31+0.19−0.15(stat)±0.03(syst). The probability to obtain the measured value, or lower, if the true double ratio is unity, is calculated to be less than 1%.