Measurement of Prompt ψ(2S) to J/ψ Yield Ratios in Pb-Pb and p-p Collisions at sqrt[s_{NN}]=2.76 TeV

Abstract

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 sqrt[s_{NN}]=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 (N_{ψ(2S)}/N_{J/ψ})_{Pb-Pb}/(N_{ψ(2S)}/N_{J/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<p_{T}<30 GeV/c, and the other at forward rapidity, 1.6<|y|<2.4, extending to lower p_{T} values, 3<p_{T}<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.