Abstract
The suppression of the individual Υ(nS) states in PbPb collisions with respect to their yields in pp data has been measured. The PbPb and pp data sets used in the analysis correspond to integrated luminosities of 150 μb(-1) and 230 nb(-1), respectively, collected in 2011 by the CMS experiment at the LHC, at a center-of-mass energy per nucleon pair of 2.76 TeV. The Υ(nS) yields are measured from the dimuon invariant mass spectra. The suppression of the Υ(nS) yields in PbPb relative to the yields in pp, scaled by the number of nucleon-nucleon collisions, R(AA), is measured as a function of the collision centrality. Integrated over centrality, the R(AA) values are 0.56±0.08(stat)±0.07(syst), 0.12±0.04(stat)±0.02(syst), and lower than 0.10 (at 95% confidence level), for the Υ(1S), Υ(2S), and Υ(3S) states, respectively. The results demonstrate the sequential suppression of the Υ(nS) states in PbPb collisions at LHC energies.
Highlights
The suppression of the individual ÇðnSÞ states in PbPb collisions with respect to their yields in pp data has been measured
The PbPb and pp data sets used in the analysis correspond to integrated luminosities of 150 bÀ1 and 230 nbÀ1, respectively, collected in 2011 by the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC), at a center-of-mass energy per nucleon pair of 2.76 TeV
The results demonstrate the sequential suppression of the ÇðnSÞ states in PbPb collisions at LHC energies
Summary
The suppression of the individual ÇðnSÞ states in PbPb collisions with respect to their yields in pp data has been measured. The CMS apparatus has extensive forward calorimetry, including two steel–quartz-fiber Cerenkov hadron forward calorimeters (HF), which cover the range 2:9 < jj < 5:2 These detectors are used for event selection and centrality determination in PbPb collisions. The background parameters are determined from the fit This nominal model accurately describes the mass sidebands in the opposite-sign muon signal sample, shown in Fig. 1 (top), as well as the alternative estimates of the shape of the combinatorial background obtained from like-sign muon pairs or via a ‘‘trackrotation’’ method. In order to investigate the dependence of the suppression on the centrality of the collision, the double ratio is displayed as a function of
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