Inclusive $\psi$(2S) production at forward rapidity in pp, p-Pb and Pb-Pb collisions with ALICE at the LHC

TL;DR

This paper reports on the measurement of inclusive $ ext{ψ}(2S)$ production across different collision systems at the LHC, revealing discrepancies with existing models and highlighting the need for new theoretical mechanisms.

Contribution

First measurement of $ ext{ψ}(2S)$ production in pp, p-Pb, and Pb-Pb collisions with detailed comparisons to models, showing the necessity for new explanations.

Findings

$ ext{ψ}(2S)$ production cross-section in pp collisions.

$ ext{ψ}(2S)$ to J/$ ext{ψ}$ cross-section ratio analysis.

$ ext{ψ}(2S)$ nuclear modification factor in p-Pb collisions.

Abstract

The ALICE Collaboration has studied inclusive $\psi$(2S) production in pp, p-Pb and Pb-Pb collisions with the ALICE Muon Spectrometer which covers the rapidity range 2.5 $<$ $y_{\rm lab}$ $<$ 4. The $\psi$(2S) measurement was performed in the dimuon decay channel. The $\psi$(2S) production cross-section and $\psi$(2S) to J/$\psi$ cross-section ratio in pp collisions will be presented, both integrated and differential in rapidity and in transverse momentum. In p-Pb collisions, $\psi$(2S) results will be compared to the J/$\psi$ ones by means of the production cross-section ratio and the double ratio [$\psi$(2S)/J/$\psi$]$_{{\mathrm {pPb}}}$/[$\psi$(2S)/J/$\psi$]$_{{\mathrm {pp}}}$ studied as a function of the resonance transverse momentum and event activity of the collision. The $\psi$(2S) nuclear modification factor, $R_{{\mathrm {pPb}}}$, will also be presented. Theoretical models based on nuclear shadowing, coherent energy loss or both cannot describe our results. Therefore other mechanisms must be invoked in order to describe the $\psi$(2S) production. Finally, results on $\psi$(2S) production in Pb-Pb collisions will be shown in two transverse momentum ranges as a function of centrality.