Measurement of Prompt ψ(2S) to J/ψ Yield Ratios in Pb-Pb and p-p Collisions at √sNN = 2.76 TeV

CMS Collaboration

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The ratio between the prompt ψ (2S) and J/ψ yields, reconstructed via their decays into μ+μ, is measured in Pb-Pb and p-p collisions at √sNN = 2.76 TeV. The analysis is based on Pb-Pb and p-p data samples collected by CMS at the Large Hadron Collider, corresponding to integrated luminosities of 150 μb−1 and 5.4 pb−1, respectively. The double ratio of measured yields (Nψ(2S)/NJ/ψ)Pb-Pb/(Nψ(2S)/NJ/ψ)p-p is computed in three Pb-Pb collision centrality bins and two kinematic ranges: one at midrapidity, |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 values, 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.
Original languageEnglish
Article number262301
Number of pages15
JournalPhysical Review Letters
Issue number26
Publication statusPublished - 2014
Externally publishedYes


  • Collisions
  • Matter effects
  • Production

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