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Analysis of charmonium production at fixed-target experiments in the NRQCD approach

F. Maltoni, J. Spengler, M. Bargiotti, A. Bertin, M. Bruschi, S. De Castro, L. Fabbri, P. Faccioli, B. Giacobbe, F. Grimaldi, I. Massa, M. Piccinini, N. Semprini-Cesari, R. Spighi, M. Villa, A. Vitale, A. Zoccoli

TL;DR

The study tests NRQCD factorization for charmonium production using next-to-leading order short-distance coefficients against a comprehensive set of fixed-target and low-energy pp data. By fitting color-octet matrix elements relative to Tevatron values, the authors find that fixed-target data require significantly smaller octet contributions, suggesting potential universality tensions or the need for higher-order corrections. The analysis highlights data consistency issues and demonstrates that, within uncertainties, NRQCD can describe trends with octet fractions suppressed compared to Tevatron results. The work provides important constraints on charmonium production mechanisms and guides future theoretical and experimental efforts in heavy-quarkonium phenomenology.

Abstract

We present an analysis of the existing data on charmonium hadro-production based on non-relativistic QCD (NRQCD) calculations at the next-to-leading order (NLO). All the data on J/psi and psi' production in fixed-target experiments and on pp collisions at low energy are included. We find that the amount of color octet contribution needed to describe the data is about 1/10 of that found at the Tevatron.

Analysis of charmonium production at fixed-target experiments in the NRQCD approach

TL;DR

The study tests NRQCD factorization for charmonium production using next-to-leading order short-distance coefficients against a comprehensive set of fixed-target and low-energy pp data. By fitting color-octet matrix elements relative to Tevatron values, the authors find that fixed-target data require significantly smaller octet contributions, suggesting potential universality tensions or the need for higher-order corrections. The analysis highlights data consistency issues and demonstrates that, within uncertainties, NRQCD can describe trends with octet fractions suppressed compared to Tevatron results. The work provides important constraints on charmonium production mechanisms and guides future theoretical and experimental efforts in heavy-quarkonium phenomenology.

Abstract

We present an analysis of the existing data on charmonium hadro-production based on non-relativistic QCD (NRQCD) calculations at the next-to-leading order (NLO). All the data on J/psi and psi' production in fixed-target experiments and on pp collisions at low energy are included. We find that the amount of color octet contribution needed to describe the data is about 1/10 of that found at the Tevatron.

Paper Structure

This paper contains 8 sections, 9 equations, 3 figures, 4 tables.

Table of Contents

  1. Introduction
  2. The NRQCD approach
  3. Present experimental situation
  4. Compilation of $J/\psi$ cross sections
  5. Compilation of $\psi(2S)$ cross sections
  6. Comments on the available data
  7. Fit results
  8. Conclusions

Figures (3)

  • Figure 1: Production cross sections in proton-induced interactions from Tab. \ref{['tab:sumexp']} as a function of the cms-energy. Proton-proton (pp) and proton-nucleus (pA) measurements are indicated by different symbols. Left: differential cross sections $d\sigma_{pN}/dy$ at $y$=0; right: total cross sections for $J/\psi$ and $\psi(2S)$ production.
  • Figure 2: Fit results as a function of the cms-energy for the $J/\psi$ cross section (top), the $\psi(2S)$ cross section (bottom-left) and the $\sigma_{\psi(2S)}/\sigma_{J/\psi}$ ratio (bottom-right). The open circles in the two bottom plots represent the results calculated from the published papers which are not used in the fit.
  • Figure 3: The $J/\psi$ differential cross section $d\sigma_{pN}/dy$ at $y$=0, as a function of the cms-energy. The data shown here are not used in the fit. The theoretical prediction with its uncertainty corresponds to the fit to the total cross sections, as shown in Fig. \ref{['fig:resfit']}.