We report the observation of the suppression of the individual Υ(nS) states in PbPb collisions. The dimuon invariant mass spectra from the 150 μb^{−1} PbPb and 230 nb^{−1} pp datasets, both produced at a centerofmass energy per nucleon pair of 2.76 TeV and collected in 2011 by the CMS experiment at the LHC, are explored, for muons of transverse momentum above 4 GeV/c and pseudorapidity between 2.4 and 2.4. The yield double ratios of excited states Υ(2S) and Υ(3S) to Υ(1S) state, for PbPb relative to pp collisions, [Υ(nS)/Υ(1S)]_{PbPb}/[Υ(nS)/Υ(1S)]_{pp}, are measured to be 0.21 ± 0.07 (stat.) ± 0.02 (syst.) for n = 2 and less than 0.1 at 95% confidence level for n = 3. Measurements of the Υ(nS) individual states are performed: their suppression is ordered as Υ(3S) > Υ(2S) > Υ(1S), and increases with the centrality of the PbPb collision.
Double ratio of the combined excited states, Y(2S)+Y(3S), relative to the ground state Y(1S), for the centralityintegrated data:
[Υ(2S+3S)/Υ(1S)]_{PbPb}/[Υ(2S+3S)/Υ(1S)]_{pp} = 0.15 ± 0.05 (stat.) ± 0.02 (syst.)
Raw signal yields:
PbPb Y(1S): 1317 ± 73 (stat.)
PbPb Y(2S): 156 ± 38 (stat.)
pp Y(1S): 88 ± 11 (stat.)
pp Y(2S): 49 ± 10 (stat.)
( click on plot to get .pdf)
Figure  Abbreviated Caption 

Dimuon invariantmass distributions from the PbPb data at sqrt(s_{NN}) = 2.76 TeV. The same reconstruction algorithm and analysis criteria are applied to PbPb and pp datasets, including a transverse momentum requirement on single muons of p_{T} > 4 GeV/c. The solid (signal + background) and dashed (backgroundonly) lines show the results of the simultaneous fit performed to the pp and PbPb datasets.  
Dimuon invariantmass distributions from the pp data at sqrt(s_{NN}) = 2.76 TeV. The same reconstruction algorithm and analysis criteria are applied to PbPb and pp datasets, including a transverse momentum requirement on single muons of p_{T} > 4 GeV/c. The solid (signal + background) and dashed (backgroundonly) lines show the results of the simultaneous fit performed to the pp and PbPb datasets.  
Centrality dependence of the double ratio [Υ(2S)/Υ(1S)]_{PbPb}/[Υ(2S)/Υ(1S)]_{pp}. The centrality bins are 05%, 510%, 1020%, 2030%, 3040%, 4050%, and 50100%. For each bin, the centrality percentile is specified; the point abscissae used correspond to the mean of the distribution of the expected number of participants N_{part} in the respective bin. The global uncertainty represented by a box at unity corresponds to the quadrature sum of statistical and systematic uncertainties from the fit to the pp data, and do not affect the pointtopoint trend.  
Centrality dependence of the nuclear modification factors, R_{AA}, for the individual Υ(1S) and Υ(2S) states. The centrality bins are 05%, 510%, 1020%, 2030%, 3040%, 4050%, and 50100%. The uncertainties of 14% for Υ(1S) and 21% for Υ(2S), from N_{part}independent quantities (luminosity, pp yields and efficiency), are represented by the boxes at unity, and are not included in the data points as these do not affect the pointtopoint trend.  
Variant of the previous plot, but also including the centralityintegrated values (minimum bias). 
( click on plot to get .pdf)
Figure  Abbreviated Caption 

Comparison of R_{AA} results for Y(nS) and 2011run J/Ψ (preliminary results). The results are shown as a function of centrality and for the centralityintegrated case, displaying the quarkonium sequential suppression observed.  
Comparison of the Υ(1S) and Υ(2S) nuclear modification factor R_{AA} centrality dependence results to the 2011run J/Ψ R_{AA} measurement (preliminary). 

Comparison of the Υ(1S) nuclear modification factor R_{AA} centrality dependence result to the 2010run Y(1S) R_{AA} previous measurement (Published in JHEP 1205 (2012) 063, preprint available at arXiv:1201.5069).  
Comparison of the Υ(1S) nuclear modification factor R_{AA} centrality dependence result to theory prediction M. Strickland (arXiv:1207.5327v2).  
Comparison of the Υ(1S) nuclear modification factor R_{AA} centrality dependence result to the Y(1S) R_{AA }measurent by STAR (arXiv:1312.3675). The STAR Results are binned in classes of centrality 010%, 1030%, 3060%. 

Strongbinding scenario (SBS) prediction, produced using the calculations performed in the paper Eur. Phys. J. A48 (2012) 72, based upon the approach developed in Phys.Rev. C 73 (2006) 064906. The significance of coldnuclearmatter effects has been simulated by employing two nuclear absorption cross sections to estimate an upper and lower bound. For LHC 0.0 mb and 2.0 mb are used to produce the bands seen in the plots. The regeneration component is calculated during plotting as "Total R_{AA}"  "Primordial R_{AA}".  
Comparison of the Υ(1S) and Υ(2S) nuclear modification factor R_{AA} centrality dependence results to the Y(1S) R_{AA }measured in the forward rapidity range (2.5<y<4) by ALICE (arXiv:1405.4493). The grey box at unity displays correlated systematic errors relative to the pp reference. On the right hand side a smaller panel is included, suggesting a comparison between centralityintegrated results. 
( click on plot to get .pdf)
Figure  Abbreviated Caption 

Dimuon invariantmass distribution from the PbPb data at sqrt(sNN) = 2.76 TeV. The red line shows the fit to the PbPb data. The blue dashed line shows the shape obtained from the fit to the pp data. For a better comparison, the background shape, background yield, mass peak width, mass peak tail shape and the Y(1S) yields in the blue line are fixed to the PbPb fit, while the Y(2S)/Y(1S) and Y(3S)/Y(1S) ratios are fixed to the pp fit values.  
Variant of the previous plot. Here, the dashed curve illustrates the corresponding signals in pp data, scaled by the R_{AA} values. The Y(1S) state is apparently suppressed in PbPb with respect to pp, while the Y(2S) and Y(3S) states are suppressed significantly more.  
Dimuon invariantmass distribution from the PbPb data at sqrt(s_{NN}) = 2.76 TeV, in the centrality bin 05%. Resolution and final state radiation fit parameters are fixed to the centralityintegrated (aka minimum bias) sample.  
Dimuon invariantmass distribution from the PbPb data at sqrt(s_{NN}) = 2.76 TeV, in the centrality bin 510%. Resolution and final state radiation fit parameters are fixed to the centralityintegrated (aka minimum bias) sample.  
Dimuon invariantmass distribution from the PbPb data at sqrt(s_{NN}) = 2.76 TeV, in the centrality bin 1020%. Resolution and final state radiation fit parameters are fixed to the centralityintegrated (aka minimum bias) sample. 

Dimuon invariantmass distribution from the PbPb data at sqrt(s_{NN}) = 2.76 TeV, in the centrality bin 2030%. Resolution and final state radiation fit parameters are fixed to the centralityintegrated (aka minimum bias) sample. 

Dimuon invariantmass distribution from the PbPb data at sqrt(s_{NN}) = 2.76 TeV, in the centrality bin 3040%. Resolution and final state radiation fit parameters are fixed to the centralityintegrated (aka minimum bias) sample. 

Dimuon invariantmass distribution from the PbPb data at sqrt(s_{NN}) = 2.76 TeV, in the centrality bin 4050%. Resolution and final state radiation fit parameters are fixed to the centralityintegrated (aka minimum bias) sample.  
Dimuon invariantmass distribution from the PbPb data at sqrt(s_{NN}) = 2.76 TeV, in the centrality bin 50100%. Resolution and final state radiation fit parameters are fixed to the centralityintegrated (aka minimum bias) sample.  

The total signal efficiency, evaluated from PbPb and pp Monte Carlo simulation; shown as a function of the centrality of the PbPb collision (expressed by the number of participant nucleons). The error bars reflect the statistics of the MC sample, and the systematic uncertainties related to the kinematic distributions and to the MC validation through comparison with data.


The Y(1S)/Y(2S) efficiency ratio, evaluated from PbPb and pp Monte Carlo simulation; shown as a function of the centrality of the PbPb collision (expressed by the number of participant nucleons). The error bars reflect the statistics of the MC sample, and the systematic uncertainties related to the kinematic distributions.

Estimations of the background shape used in the evaluation of systematic fit uncertainties, based on: (top) likesign, (middle) trackrotated, and (bottom) oppositesign dimuon spectra. 
I  Attachment  History  Action  Size  Date  Who  Comment 

Raa_AliceY1SY2S_MB_v2.pdf  r1  manage  17.9 K  20130820  19:27  NicolasFilipovic  
png  Raa_AliceY1SY2S_MB_v2.png  r1  manage  139.6 K  20130820  20:27  NicolasFilipovic  
Raa_AliceY1SY2S_MB_vFinal.pdf  r1  manage  17.8 K  20140702  12:24  NicolasFilipovic  
png  UpsilonQM2014.png  r1  manage  18.5 K  20140520  15:47  NicolasFilipovic  
png  UpsilonQMSTAR.png  r1  manage  13.7 K  20140520  15:47  NicolasFilipovic  
png  upsilon_RAA_CMSSTAR.png  r1  manage  104.9 K  20141120  11:25  LamiaBenhabib  
upsilon_RAA_CMSSTAR_2014.pdf  r1  manage  16.7 K  20140702  12:24  NicolasFilipovic 