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Quarkonium Photoproduction at Next-to-leading Order

F. Maltoni, M. L. Mangano, A. Petrelli

TL;DR

The paper delivers a complete next-to-leading order computation of heavy-quarkonium photoproduction cross sections for color-octet S- and P-waves within the NRQCD framework, employing covariant projections in $D$ dimensions to regulate divergences. It carefully isolates soft and collinear infrared structures, showing how they factorize and cancel between real and virtual contributions, and how collinear poles are absorbed into PDFs in the MSbar scheme. The results reveal that NLO corrections reduce scale dependence at moderate $\gamma p$ energies but introduce large small-$x$ corrections at higher energies, making predictions sensitive to gluon densities and factorization scale. The work provides a comprehensive set of analytic expressions and a robust methodology for NLO quarkonium photoproduction and its phenomenological implications for high-energy processes.

Abstract

We present the calculation of O(as^2 aem) corrections to heavy-quarkonium total photoproduction cross-sections. Results are given for the colour-octet component of S and P waves. The calculation is performed using covariant projectors in dimensional regularization. A phenomenological study of the results, including a discussion of the high-energy behaviour of the cross sections, is presented. For gamma-p energies up to few hundred GeV the NLO corrections significantly reduce the scale dependence of the production rates relative to the Born-level results. Large small-x corrections arise at higher energies, making the predictions strongly dependent on the shape of the gluon density and on the choice of factorization scale.

Quarkonium Photoproduction at Next-to-leading Order

TL;DR

The paper delivers a complete next-to-leading order computation of heavy-quarkonium photoproduction cross sections for color-octet S- and P-waves within the NRQCD framework, employing covariant projections in dimensions to regulate divergences. It carefully isolates soft and collinear infrared structures, showing how they factorize and cancel between real and virtual contributions, and how collinear poles are absorbed into PDFs in the MSbar scheme. The results reveal that NLO corrections reduce scale dependence at moderate energies but introduce large small- corrections at higher energies, making predictions sensitive to gluon densities and factorization scale. The work provides a comprehensive set of analytic expressions and a robust methodology for NLO quarkonium photoproduction and its phenomenological implications for high-energy processes.

Abstract

We present the calculation of O(as^2 aem) corrections to heavy-quarkonium total photoproduction cross-sections. Results are given for the colour-octet component of S and P waves. The calculation is performed using covariant projectors in dimensional regularization. A phenomenological study of the results, including a discussion of the high-energy behaviour of the cross sections, is presented. For gamma-p energies up to few hundred GeV the NLO corrections significantly reduce the scale dependence of the production rates relative to the Born-level results. Large small-x corrections arise at higher energies, making the predictions strongly dependent on the shape of the gluon density and on the choice of factorization scale.

Paper Structure

This paper contains 7 sections, 47 equations, 3 figures.

Table of Contents

  1. Introduction
  2. Introduction to the formalism
  3. Soft factorization and the calculation of higher-order corrections
  4. Soft factorization in $gg \gamma$ amplitudes
  5. Kinematics and factorization of soft and collinear singularities
  6. Results
  7. $g\gamma \to g\cal{O}$O$^{[8]}$ processes

Figures (3)

  • Figure 1: Diagrams for the $g\gamma$ Born amplitudes.
  • Figure 2: Diagrams for the real corrections to the $g\gamma$ channels. Permutations of outgoing gluons and/or reversal of fermion lines are always implied.
  • Figure :