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Re-visiting Direct $J/ψ$ Production at the Fermilab Tevatron

K. Hagiwara, W. Qi, C. F. Qiao, J. X. Wang

TL;DR

This work re-examines direct J/ψ production at the Tevatron in light of BaBar/Belle observations that charm fragmentation and higher-order effects are sizable. It employs a fragmentation-dominated, factorized framework that includes charm-sea induced processes and empirical K-factors to represent corrections beyond leading order. The results indicate that color-singlet mechanisms, especially via charm-sea channels, can account for a substantial portion (and potentially all, with large K) of the observed high-pT yield, while predicting unpolarized J/ψ at high pT as a key discriminant. The findings challenge the necessity of large color-octet contributions and propose polarization measurements, along with LHC data, as decisive tests of the underlying production dynamics.

Abstract

We re-analyze the direct $\jp$ production processes at the Fermilab Tevatron in view of the recent observation at the B-factories, where both $\jp$ inclusive and exclusive production rates are found to be about an order of magnitude larger than the leading order estimates of non-relativistic QCD. The charm quark fragmentation to $\jp$, which is the dominant color-singlet process at high $p_T$, is normalized by the B-factory measurements. The process receives further enhancement due to the charm sea contribution which has so far been ignored in most analyses. After summing up all sub-process contributions, we find that the color-singlet mechanism alone can account for 20% to 90% of the observed direct $\jp$ high $p_T$ production. The polarization rate of the directly produced $\jp$ is sensitive to the fraction of the color-octet contribution, which is employed to fill the gap between the color-singlet prediction and experimental data. With a bigger $K$-factor for the charm quark fragmentation probability, we envisage a smaller matrix element for the color-octet $^3S_1^{(8)}$ state, and this can be examined at the LHC in near future.

Re-visiting Direct $J/ψ$ Production at the Fermilab Tevatron

TL;DR

This work re-examines direct J/ψ production at the Tevatron in light of BaBar/Belle observations that charm fragmentation and higher-order effects are sizable. It employs a fragmentation-dominated, factorized framework that includes charm-sea induced processes and empirical K-factors to represent corrections beyond leading order. The results indicate that color-singlet mechanisms, especially via charm-sea channels, can account for a substantial portion (and potentially all, with large K) of the observed high-pT yield, while predicting unpolarized J/ψ at high pT as a key discriminant. The findings challenge the necessity of large color-octet contributions and propose polarization measurements, along with LHC data, as decisive tests of the underlying production dynamics.

Abstract

We re-analyze the direct production processes at the Fermilab Tevatron in view of the recent observation at the B-factories, where both inclusive and exclusive production rates are found to be about an order of magnitude larger than the leading order estimates of non-relativistic QCD. The charm quark fragmentation to , which is the dominant color-singlet process at high , is normalized by the B-factory measurements. The process receives further enhancement due to the charm sea contribution which has so far been ignored in most analyses. After summing up all sub-process contributions, we find that the color-singlet mechanism alone can account for 20% to 90% of the observed direct high production. The polarization rate of the directly produced is sensitive to the fraction of the color-octet contribution, which is employed to fill the gap between the color-singlet prediction and experimental data. With a bigger -factor for the charm quark fragmentation probability, we envisage a smaller matrix element for the color-octet state, and this can be examined at the LHC in near future.

Paper Structure

This paper contains 3 sections, 2 equations, 2 figures.

Table of Contents

  1. INTRODUCTION
  2. CALCULATION AND RESULTS OF THE $J/\psi$ HIGH $p_T$ PRODUCTION
  3. CONCLUSIONS

Figures (2)

  • Figure 1: Direct $J/\psi$ production differential cross-sections for various color-singlet processes versus the Run-I experimental data from the Fermilab Tevatron.
  • Figure 2: NRQCD prediction for the direct $J/\psi$ production at the Tevatron Run I energy, where the color-octet matrix element is adjusted in order to fill the gap between CS prediction and experimental data. (a) The normalization factor for the charm fragmentation process is $4\times2$, 4 for $K$-factor and 2 for hard-scattering cross-section; (b) the normalization factor is taken to be $8\times2$. (c) The $J/\psi$ polarization variable $\alpha$ versus transverse momentum.