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Physical Review Letters 109 (2012) 222301
Observation of sequential Upsilon suppression in PbPb collisions
S. Chatrchyan, M. Besancon1, S. Choudhury1, M. Dejardin1, D. Denegri1, B. Fabbro1, J.L. Faure1, F. Ferri1, S. Ganjour1, A. Givernaud1, P. Gras1, G. Hamel de Monchenault1, P. Jarry1, E. Locci1, J. Malcles1, L. Millischer1, A. Nayak1, J. Rander1, A. Rosowsky1, I. Shreyber1, M. Titov1, S. Baffioni2, F. Beaudette2, L. Benhabib2, L. Bianchini2, M. Bluj2, C. Broutin2, Pierre Busson2, C. Charlot2, N. Daci2, T. Dahms2, L. Dobrzynski2, R. Granier de Cassagnac2, M. Haguenauer2, P. Mine2, C. Mironov2, I.N. Naranjo2, M. Nguyen2, C. Ochando2, P. Paganini2, D. Sabes2, R. Salerno2, Y. Sirois2, C. Veelken2, A. Zabi2, J.-L. Agram3, J. Andrea3, D. Bloch3, D. Bodin3, J.-M. Brom3, M. Cardaci3, E.C. Chabert3, C. Collard3, E. Conte3, F. Drouhin3, C. Ferro3, J.-C. Fontaine3, D. Gele3, U. Goerlach3, P. Juillot3, A.-C. Le Bihan3, P. Van Hove3, F. Fassi4, D. Mercier4, S. Beauceron5, N. Beaupere5, O. Bondu5, G. Boudoul5, J. Chasserat5, R. Chierici5, D. Contardo5, P. Depasse5, H. El Mamouni5, J. Fay5, S. Gascon5, M. Gouzevitch5, B. Ille5, T. Kurca5, M. Lethuillier5, L. Mirabito5, S. Perries5, V. Sordini5, Y. Tschudi5, P. Verdier5, S. Viret5
For the CMS collaboration(s)
(2012)

The suppression of the individual Upsilon(nS) states in PbPb collisions with respect to their yields in pp data has been measured. The PbPb and pp datasets used in the analysis correspond to integrated luminosities of 150 inverse microbarns and 230 inverse nanobarns, 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 Upsilon(nS) yields are measured from the dimuon invariant mass spectra. The suppression of the Upsilon(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 Upsilon(1S), Upsilon(2S), and Upsilon(3S) states, respectively. The results demonstrate the sequential suppression of the Upsilon(nS) states in PbPb collisions at LHC energies.
1:  IRFU - Institut de Recherches sur les lois Fondamentales de l'Univers (ex DAPNIA)
2:  LLR - Laboratoire Leprince-Ringuet
3:  IPHC - Institut Pluridisciplinaire Hubert Curien
4:  CC IN2P3 - Centre de Calcul de l'inst. national de phy. nucléaire et de phy. des particules
5:  IPNL - Institut de Physique Nucléaire de Lyon
Physics/High Energy Physics - Experiment

Physics/Nuclear Experiment
Fulltext link: 
http://fr.arXiv.org/abs/1208.2826