A systematic study of J/psi suppression in cold nuclear matter

TL;DR

The paper determines the J/ψ–nucleon inelastic cross section by fitting a Glauber-model-based absorption factor to a broad set of J/ψ production data on nuclear targets, spanning hadroproduction and leptoproduction, and examines the influence of nuclear parton densities. It finds σ_{J/ψN}≈3.4–3.5 mb, with small changes when including nDS nuclear PDFs, but larger cross sections if stronger gluon shadowing is assumed, indicating substantial uncertainties from nPDFs. The analysis highlights tensions among datasets and emphasizes proper treatment of correlated systematics in χ^2 fits. These results provide a baseline for cold nuclear matter effects in heavy-ion J/ψ suppression and compare favorably with phenomenological expectations like vector dominance models while being somewhat smaller than earlier global estimates.

Abstract

Based on a Glauber model, a statistical analysis of all mid-rapidity J/psi hadroproduction and leptoproduction data on nuclear targets is carried out. This allows us to determine the J/psi-nucleon inelastic cross section, whose knowledge is crucial to interpret the J/psi suppression observed in heavy-ion collisions, at SPS and at RHIC. The values of sigma are extracted from each experiment. A clear tension between the different data sets is reported. The global fit of all data gives sigma=3.4+/-0.2 mb, which is significantly smaller than previous estimates. A similar value, sigma=3.5+/-0.2 mb, is obtained when the nDS nuclear parton densities are included in the analysis, although we emphasize that the present uncertainties on gluon (anti)shadowing do not allow for a precise determination of sigma. Finally, no significant energy dependence of the J/psi-N interaction is observed, unless strong nuclear modifications of the parton densities are assumed.

Figures (5)

• Figure 1: The ratio of the gluon distribution in a gold nucleus over that in a proton, $R_g^{\rm Au}(x, m_{_{J/\psi}}^2$), plotted as a function of Bjorken-$x$ using the nDS, nDSg, EKS and HKM parametrizations.
• Figure 2: Values of the $J/\psi$--N inelastic cross section extracted from each data set. The solid (dashed) horizontal bars indicate the (rescaled) $1\sigma$ error, $\delta \sigma_{_{J/\psi {\rm N}}}$ ($\delta \bar{\sigma}_{_{J/\psi {\rm N}}}$), and the dashed band represents the value obtained from the global fit of all data.
• Figure 3: The relative uncertainty of the $J/\psi$--N inelastic cross section, $\delta \sigma_{_{J/\psi {\rm N}}} / \sigma_{_{J/\psi {\rm N}}}$, plotted versus the values of $\chi^2/{\rm ndf}$ obtained from each data sample.
• Figure 4: The $J/\psi$--N cross section extracted from each data set and in the global fit, using the nDS ($\sigma^{{\small {\rm nDS}}}_{_{J/\psi {\rm N}}}$) versus EKS ($\sigma^{{\small {\rm EKS}}}_{_{J/\psi {\rm N}}}$) nuclear parton densities.
• Figure 5: The $J/\psi$--N cross section extracted from each data set as a function of $x_{_2}$. The solid (dashed) vertical bars indicate the (rescaled) 1$\sigma$ error, $\delta \sigma_{_{J/\psi {\rm N}}}$ ($\delta \bar{\sigma}_{_{J/\psi {\rm N}}}$), and the dashed band represents the value obtained from the global fit of all data.