Study of ϒ(𝑛𝑆), 𝐽/𝜓 and 𝜓(2𝑆) production in PbPb collisions at LHCb

Abstract

The production of ϒ(𝑛𝑆) (𝑛 = 1, 2, 3), 𝐽/𝜓, and 𝜓(2𝑆) mesons has been studied in lead-lead collisions at the LHCb. In the search for Quark-Gluon Plasma, which suppresses more considerably excited states, the yield ratio between 𝑞¯𝑞(2𝑆) and 𝑞¯𝑞(1𝑆) (𝑞 = 𝑏, 𝑐) has been computed. The dimuon decay channel is considered to reconstruct the invariant mass of the quarkonia states, and unbinned maximum-likelihood fits are used to extract the yields. For ϒ(𝑛𝑆), we find insufficient evidence for the production of ϒ(2𝑆), leading to an upper bound on the excited-to-ground state ratio of 0.09, significantly lower than the corresponding proton-proton collision value of 0.25 ± 0.01, suggesting suppression. For charmonium, we distinguish between prompt and non-prompt production using the pseudo decay time and report a 𝜓(2𝑆)-to-𝐽/𝜓 yield ratio of 0.022 ± 0.004, which remains inconclusive but compatible with previous results from 𝑝𝑝 collisions.