Study of psi' and chi_c decays as feed-down sources of J/psi hadro-production

TL;DR

This study determines the J/psi feed-down fractions from heavier charmonia in pp collisions by analyzing mid-rapidity hadro-production data within a Glauber absorption framework. The authors extract a pp reference feed-down $R^0(\psi^\prime) = (8.1 \pm 0.3)\%$ and $R^0(\chi_c) = (25 \pm 5)\%$, highlighting how differences in nuclear absorption between states influence these values. The work emphasizes mid-rapidity data to avoid forward-$x_F$ effects and discusses energy-dependent trends observed at higher collider energies, while noting limitations of the simple absorption model and the need for more precise measurements and better theoretical treatment of pre-resonance states. Overall, the results provide essential baselines for interpreting J/psi suppression as a probe of deconfined QCD matter in nuclear collisions.

Abstract

The interpretation of the J/psi suppression patterns observed in nuclear collisions, at CERN and RHIC, as a signature of the formation of a deconfined phase of QCD matter, requires knowing which fractions of the measured J/psi yields, in pp collisions, are due to decays of heavier charmonium states. From a detailed analysis of the available mid-rapidity charmonium hadro-production cross sections, or their ratios, we determine that the J/psi feed-down contributions from psi' and chi_c decays are, respectively, (8.1 +/- 0.3) % and (25 +/- 5) %. These proton-proton values are derived from global averages of the proton-nucleus measurements, assuming that the charmonium states are exponentially absorbed with the length of matter they traverse in the nuclear targets.

Figures (4)

• Figure 1: The $\rho(\psi^\prime)$ values as a function of the nuclear path length, $L$, from NA50/51 measurements at 400 GeV (a) and 450 GeV (b), and the $\rho(\psi^\prime)_{\mathrm{W}}\,/\,\rho(\psi^\prime)_{\mathrm{Be}}$ ratio measured by E866, in the $-0.1<x_{\mathrm{F}}<0.2$ window (c). The curves are the result of the global fit described in the text, including (dashed lines) or excluding (solid lines) the NA51 points.
• Figure 2: $68\,\%$ (solid lines) and $99\,\%$ (dashed lines) confidence level contours for the bi-dimensional probability distribution of the parameters $R^0(\psi^\prime)$ and $\sigma_{\mathrm{abs}}(\psi^\prime)-\sigma_{\mathrm{abs}}(\mathrm{J}/\psi+\chi_c)$. The thick black contours delimit the region favoured by the global fit, while the thin coloured (or grey) ones reflect the individual data sets.
• Figure 3: The $R(\chi_c)$ measurements used in the present analysis as a function of the nuclear path length $L$. The curve is the result of the fit described in the text (excluding the first point).
• Figure 4: $68\,\%$ and $99\,\%$ confidence level contours for the bi-dimensional probability distribution of the fit parameters $R^0(\chi_c)$ and $\sigma_{\mathrm{abs}}(\chi_c)-\sigma_{\mathrm{abs}}(\mathrm{J}/\psi+\psi^\prime)$.