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

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 √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.