Prompt and non-prompt J / ψ and ψ ( 2 S ) suppression at high transverse momentum in 5.02 TeV Pb+Pb collisions with the ATLAS experiment

Abstract

A measurement of $J/\psi$ and $\psi \left(2S\right)$ 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 $\psi \left(2S\right)$ is observed to be stronger than that of $J/\psi$ , while the suppression of non-prompt $\psi \left(2S\right)$ 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.

Fig. 1

(Left) Inverse total weight binned in the dimuon transverse momentum and rapidity for integrated centrality as estimated in MC simulation and corrected for differences between efficiencies in MC and experimental data. Decreases in efficiency at very central rapidity correspond to the $|\eta |<0.1$ region not covered by the muon detectors. The weight is dominated by the acceptance correction. (Right) Muon reconstruction efficiency as a function of the summed transverse energy in the forward calorimeters, $\sum E_{\text{T}}^{\mathrm{FCal}}$

Fig. 2

Dimuon invariant mass for events with $2.6<m_{\mu \mu }<4.2\text{GeV}$ (left) and dimuon pseudo-proper lifetime (right). The data, corrected for acceptance times efficiency, are shown for the range $9<p_{\text{T}}<40\text{GeV}$, $|y|<2.0$, and centrality 20–50% in Pb+Pb collisions. Superimposed on the data are the projections of the fit results

Fig. 3

Pb+Pb per-event yields of prompt $J/\psi$ (left) and non-prompt $J/\psi$ (right) as a function of $p_{\text{T}}$ for three different centrality slices in the rapidity range $|y|<2$. The centroids of the $p_{\text{T}}$ bins are the mean value of the transverse momentum distributions of dimuons in the $J/\psi$ mass region, corrected for acceptance $\times$ efficiency. The vertical error bars are the combined systematic and statistical uncertainties, where the dominant source is the systematic uncertainty with the exception of the latest bin. Overlaid is a band representing the variation of the result in various spin-alignment scenarios

Fig. 4

(Left) Non-prompt fraction of $J/\psi$ production in 5.02 TeV Pb+Pb collision data as a function of $p_{\text{T}}$ for three different centrality slices in the rapidity range $|y|<2$. (Right) Comparison with the ATLAS 5.02 TeV $\mathit{pp}$ collision data [25]. The vertical error bars are the combined systematic and statistical uncertainties, dominated by the statistical uncertainty

Fig. 5

The nuclear modification factor as a function of $p_{\text{T}}$ for the prompt $J/\psi$ (left) and non-prompt $J/\psi$ (right) for $|y|<2$, in 0–80% centrality bin (top) and in 0–10%, 20–40%, and 40–80% centrality bins (bottom). The statistical uncertainty of each point is indicated by a narrow error bar. The error box plotted with each point represents the uncorrelated systematic uncertainty, while the shaded error box at $R_{\mathrm{AA}}$=1 represents correlated scale uncertainties

Fig. 6

(Left) Comparison of prompt and non-prompt $J/\psi$ $R_{\text{AA}}$ with the $R_{\text{AA}}$ of charged particles [49] and D-mesons [51]. (Right) Comparison of the $R_{\text{AA}}$ for prompt $J/\psi$ production with different theoretical models. The statistical uncertainty of each point is indicated by a narrow error bar. The error box plotted with each point represents the uncorrelated systematic uncertainty, while the shaded error box at $R_{\mathrm{AA}}$=1 represents correlated scale uncertainties

Fig. 7

The nuclear modification factor as a function of rapidity for the prompt $J/\psi$ (left) and non-prompt $J/\psi$ (right) for $9<p_{\text{T}}<40\text{GeV}$, in 0–80% centrality bin (top) and in 0–10%, 20–40%, and 40–80% centrality bins (bottom). The statistical uncertainty of each point is indicated by a narrow error bar. The error box plotted with each point represents the uncorrelated systematic uncertainty, while the shaded error box at $R_{\mathrm{AA}}$=1 represents correlated scale uncertainties

Fig. 8

The nuclear modification factor as a function of the number of participants, $N_{\mathrm{part}}$, for the prompt $J/\psi$ (left) and non-prompt $J/\psi$ (right) for $9<p_{\text{T}}<40\text{GeV}$ and for rapidity $|y|<2$. The statistical uncertainty of each point is indicated by a narrow error bar. The error box plotted with each point represents the uncorrelated systematic uncertainty, while the shaded error box at $R_{\mathrm{AA}}$=1 represents correlated scale uncertainties

Fig. 9

$\psi (2\mathrm{S})$ to $J/\psi$ double ratio, as a function of the number of participants, $N_{\mathrm{part}}$, for prompt meson production compared with different theoretical models (left) and non-prompt meson production (right). The narrow error bar represents the statistical uncertainties while the error box represents the total systematic uncertainty