CMS Collaboration, Adair, A., Akgun, B., et al.. "Measurement of Prompt ψ(2S) to J/ψ Yield Ratios in Pb-Pb and p-p Collisions at √sNN=2.76 TeV." Physical Review Letters, 113, (2014) 262301. http://dx.doi.org/10.1103/PhysRevLett.113.262301.
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.
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