Measurement of prompt psi(2S) to J/psi yield ratios in PbPb and pp collisions at sqrt(s[NN]) = 2.76 TeV

TL;DR

This study measures the ratio of prompt psi(2S) to J/psi yields in PbPb and pp collisions at 2.76 TeV, revealing how quarkonium production varies with collision centrality and kinematic range at the LHC.

Contribution

It provides the first detailed measurement of the double ratio of psi(2S) to J/psi yields in PbPb versus pp collisions across different centralities and kinematic ranges.

Findings

Double ratio varies significantly with centrality and rapidity.

In central collisions, the double ratio is notably suppressed at midrapidity.

At forward rapidity, the double ratio approaches unity, indicating different suppression patterns.

Abstract

The ratio between the prompt psi(2S) and J/psi yields, reconstructed via their decays into muon pairs, is measured in PbPb and pp collisions at sqrt(s[NN]) = 2.76 TeV. The analysis is based on PbPb and pp data samples collected by CMS at the LHC, corresponding to integrated luminosities of 150 inverse microbarns and 5.4 inverse picobarns, respectively. The double ratio of measured yields, (N[psi(2S)]/N[J/psi])[PbPb] / (N[psi(2S)]/ N[J/psi])[pp], is computed in three PbPb collision centrality bins and two kinematic ranges: one at midrapidity, abs(y) < 1.6, covering the transverse momentum range 6.5 < pt < 30 GeV/c, and the other at forward rapidity, 1.6 < abs(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.