Measurement of prompt ψ(2S) to J/ψ yield ratios in PbPb and pp collisions at √sNN = 2.76 TeV

Khachatryan, V. and Sirunyan, A. M. and Tumasyan, A. and Adam, W. and Bergauer, T. and Dragicevic, M. and Erö, J. and Fabjan, C. and Friedl, M. and Frühwirth, R. and Ghete, V. M. and Hartl, C. and Hörmann, N. and Hrubec, J. and Jeitler, M. and Kiesenhofer, W. and Knünz, V. and Krammer, M. and Krätschmer, I. and Liko, D. and Mikulec, I. and Rabady, D. and Rahbaran, B. and Rohringer, H. and Schöfbeck, R. and Strauss, J. and Taurok, A. and Treberer-Treberspurg, W. and Waltenberger, W. and Wulz, C. -E. and Filipovic, Nicolas and Bencze, György and Hajdu, Csaba and Hidas, Pál and Horváth, Dezső and Siklér, Ferenc and Veszprémi, Viktor and Vesztergombi, György and Zsigmond, Anna Júlia and Béni, Noémi Tekla and Karancsi, János and Molnár, József and Pálinkás, József and Szillási, Zoltán and Raics, Péter and Trócsányi, Zoltán and Ujvári, Balázs and Veres, Gábor (2014) Measurement of prompt ψ(2S) to J/ψ yield ratios in PbPb and pp collisions at √sNN = 2.76 TeV. PHYSICAL REVIEW LETTERS, 113 (26). ISSN 0031-9007

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Abstract

The ratio between the prompt ψ(2S) and J/ψ yields, reconstructed via their decays into μ+μ−, is measured in PbPb and pp collisions at √sNN = 2.76 TeV. The analysis is based on PbPb and pp data samples collected by CMS at the Large Hadron Col- lider, corresponding to integrated luminosities of 150 μb−1 and 5.4 pb−1, respectively. The double ratio of measured yields, (Nψ(2S)/NJ/ψ)PbPb/(Nψ(2S)/NJ/ψ)pp, is computed in three PbPb collision centrality bins and two kinematic ranges: one at midrapid- ity, |y| < 1.6, covering the transverse momentum range 6.5 < pT < 30 GeV/c, and the other at forward rapidity, 1.6 < |y| < 2.4, extending to lower pT val- ues, 3 < pT < 30 GeV/c. The centrality-integrated double ratio changes from 0.45 ± 0.13 (stat) ± 0.07 (syst) in the first range to 1.67 ± 0.34 (stat) ± 0.27 (syst) in the second. This difference is most pronounced in the most central collisions.

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