Abstract
A measurement of J/psi and psi (2mathrm {S}) production is presented. It is based on a data sample from Pb+Pb collisions at sqrt{s_{mathrm {NN}}} = 5.02~mathrm {TeV} and pp collisions at sqrt{s} = 5.02~mathrm {TeV} recorded by the ATLAS detector at the LHC in 2015, corresponding to an integrated luminosity of 0.42~mathrm {nb}^{-1} and 25~mathrm {pb}^{-1} in Pb+Pb and pp, respectively. The measurements of per-event yields, nuclear modification factors, and non-prompt fractions are performed in the dimuon decay channel for 9< p_{T}^{mu mu } < 40 GeV in dimuon transverse momentum, and -2< y_{mu mu } < 2 in rapidity. Strong suppression is found in Pb+Pb collisions for both prompt and non-prompt J/psi , increasing with event centrality. The suppression of prompt psi (2mathrm {S}) is observed to be stronger than that of J/psi , while the suppression of non-prompt psi (2mathrm {S}) is equal to that of the non-prompt J/psi within uncertainties, consistent with the expectation that both arise from b-quarks propagating through the medium. Despite prompt and non-prompt J/psi arising from different mechanisms, the dependence of their nuclear modification factors on centrality is found to be quite similar.
Highlights
There have been numerous experimental and theoretical investigations since that have demonstrated that other effects are present in addition to colour screening in a deconfined plasma [4–6]
It has been shown that over a wide range of interaction energies there is already a modification in the production of J/ψ mesons in systems where a large volume of quark–gluon plasma does not appear to form, such as in proton–nucleus collisions [7–9]. It has been shown by the ALICE Collaboration that a suppression of quarkonium is observed in ion–ion collisions as reported by several collaborations [10–14], and an enhancement may play a role leading to an increase in the observed yields of J/ψ at low transverse momentum, pT, relative to higher transverse momenta [15,16]
This paper reports measurements of prompt and nonprompt per-event yields, non-prompt fraction and nuclear modification factors, RAA, of the J/ψ√and ψ(2S)
Summary
There have been numerous experimental and theoretical investigations since that have demonstrated that other effects are present in addition to colour screening in a deconfined plasma [4–6]. It has been shown that over a wide range of interaction energies there is already a modification in the production of J/ψ mesons in systems where a large volume of quark–gluon plasma does not appear to form, such as in proton–nucleus collisions [7–9]. It has been shown by the ALICE Collaboration that a suppression of quarkonium is observed in ion–ion collisions as reported by several collaborations [10–14], and an enhancement may play a role leading to an increase in the observed yields of J/ψ at low transverse momentum, pT, relative to higher transverse momenta [15,16].
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