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TEVATRON-HERA Colour-Octet Charmonium Anomaly Versus Higher-Order QCD Effects

Bernd A. Kniehl, Gustav Kramer

TL;DR

Addresses the Tevatron–HERA discrepancy in J/psi production within NRQCD by incorporating dominant higher-order QCD effects from multiple-gluon radiation and performing a two-step fit to Tevatron data to extract color-octet matrix elements. Shows that the combination M_r^{J/psi} is substantially reduced, which lowers the predicted inelastic J/psi photoproduction cross-section excess at high z and weakens the tension with HERA. Provides LO predictions for chi_{cJ} photoproduction with feed-down to J/psi and discusses missing NLO corrections as a caveat. Overall, the work suggests NRQCD remains viable when HO effects are accounted, though a full NLO treatment is still needed.

Abstract

Approximately taking into account the higher-order effects due to multiple-gluon initial-state radiation, we extract from the latest Tevatron data of prompt J/psi hadroproduction the leading colour-octet matrix elements within the nonrelativistic-QCD (NRQCD) factorization formalism proposed by Bodwin, Braaten, and Lepage. We find that the matrix elements which describe the formation of J/psi mesons from colour-octet cc-bar pairs in the angular-momentum states ^{2S+1}L_J = ^1S_0 and ^3P_J, with J = 0,1,2, which are responsible for the excess of the predicted cross section of inelastic J/psi photoproduction over the existing HERA data at high values of the inelasticity variable z, are significantly reduced. We conclude that it is premature to proclaim a discrepancy between the Tevatron and HERA measurements of inclusive J/psi production in the NRQCD framework. We also consider J/psi mesons originating from the radiative feed down of promptly produced chi_{cJ} mesons.

TEVATRON-HERA Colour-Octet Charmonium Anomaly Versus Higher-Order QCD Effects

TL;DR

Addresses the Tevatron–HERA discrepancy in J/psi production within NRQCD by incorporating dominant higher-order QCD effects from multiple-gluon radiation and performing a two-step fit to Tevatron data to extract color-octet matrix elements. Shows that the combination M_r^{J/psi} is substantially reduced, which lowers the predicted inelastic J/psi photoproduction cross-section excess at high z and weakens the tension with HERA. Provides LO predictions for chi_{cJ} photoproduction with feed-down to J/psi and discusses missing NLO corrections as a caveat. Overall, the work suggests NRQCD remains viable when HO effects are accounted, though a full NLO treatment is still needed.

Abstract

Approximately taking into account the higher-order effects due to multiple-gluon initial-state radiation, we extract from the latest Tevatron data of prompt J/psi hadroproduction the leading colour-octet matrix elements within the nonrelativistic-QCD (NRQCD) factorization formalism proposed by Bodwin, Braaten, and Lepage. We find that the matrix elements which describe the formation of J/psi mesons from colour-octet cc-bar pairs in the angular-momentum states ^{2S+1}L_J = ^1S_0 and ^3P_J, with J = 0,1,2, which are responsible for the excess of the predicted cross section of inelastic J/psi photoproduction over the existing HERA data at high values of the inelasticity variable z, are significantly reduced. We conclude that it is premature to proclaim a discrepancy between the Tevatron and HERA measurements of inclusive J/psi production in the NRQCD framework. We also consider J/psi mesons originating from the radiative feed down of promptly produced chi_{cJ} mesons.

Paper Structure

This paper contains 5 sections, 6 equations, 2 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Theoretical input
  3. Fit to the data of charmonium hadroproduction
  4. Predictions for charmonium photoproduction
  5. Conclusions

Figures (2)

  • Figure 1: (a) LO and (b) HO-improved fits to the CDF data on the inclusive hadroproduction of prompt $J/\psi$ mesons cdf, which come in the form of $d\sigma/dp_T$ integrated over $|\eta|<0.6$ as a function of $p_T$. The fragmentation results are only shown for $p_T\ge10.91$ GeV, while the fusion results are displayed over the full $p_T$ range.
  • Figure :