[Paper Review] Exclusive production of light vector mesons at next-to-leading order in the dipole picture

Heikki Mäntysaari, Jani Penttala|arXiv (Cornell University)|Mar 31, 2022

High-Energy Particle Collisions ResearchPhysics and Astronomy78 references38 citations

TL;DR

This paper presents next-to-leading order (NLO) calculations for exclusive light vector meson production in deep inelastic scattering within the dipole picture, using light-cone perturbation theory and a mixed coordinate-momentum space formalism. It derives a finite, divergence-free cross section expression that shows excellent agreement with HERA data for φ and ρ mesons at high virtuality, with NLO corrections being numerically significant but largely captured by nonperturbative dipole evolution parameters.

ABSTRACT

Exclusive production of light vector mesons in deep inelastic scattering is calculated at next-to-leading order in the dipole picture in the limit of high photon virtuality. The resulting expression is free of any divergences and suitable for numerical evaluations. The higher-order corrections are found to be numerically important, but they can be mostly captured by the nonperturbative fit parameters describing the initial condition for the small-$x$ evolution of the dipole scattering amplitude. The vector meson production cross section is shown to depend only weakly on the meson distribution amplitude and the factorization scale. We also present phenomenological comparisons of our result to the existing exclusive $\phi$ and $ ho$ production data from HERA and find an excellent agreement at high virtualities.

Motivation & Objective

• To calculate exclusive light vector meson production at next-to-leading order (NLO) in the dipole picture for high photon virtuality.
• To provide a finite, numerically stable expression for the NLO cross section free of divergences.
• To assess the numerical impact of NLO corrections on vector meson production rates.
• To evaluate the dependence of the cross section on meson distribution amplitudes, factorization scales, and regularization schemes.
• To compare the NLO predictions with existing HERA data on φ and ρ meson production.

Proposed method

• Uses light-cone perturbation theory in mixed transverse coordinate and longitudinal momentum fraction space.
• Calculates NLO corrections to the light vector meson wave function at leading twist.
• Applies a rapidity divergence subtraction scheme from Refs. [46, 51, 54, 55] to ensure physical results.
• Combines the NLO meson wave function with the NLO virtual photon wave function and dipole-target scattering amplitude.
• Employs the Balitsky-Kovchegov (BK) equation with NLO corrections for small-x evolution of the dipole amplitude.
• Performs phenomenological comparisons using existing dipole amplitude fits to HERA data.

Experimental results

Research questions

• RQ1 How do NLO corrections affect the exclusive production cross section of light vector mesons in deep inelastic scattering?
• RQ2 To what extent do the NLO corrections depend on the meson distribution amplitude and factorization scale?
• RQ3 How sensitive is the NLO cross section to the choice of regularization scheme (CDR vs. FDH)?
• RQ4 Can the NLO dipole model description reproduce existing HERA data for φ and ρ meson production at high Q²?
• RQ5 What is the role of the infrared cutoff in the ERBL evolution of the distribution amplitude, and how does it affect the cross section?

Key findings

• The NLO cross section is finite and free of divergences, making it suitable for numerical evaluation.
• NLO corrections are numerically important but largely absorbed into the nonperturbative fit parameters of the dipole amplitude's initial condition.
• The cross section depends only weakly on the meson distribution amplitude and factorization scale, with variations of at most ∼2%.
• The ratio of cross sections in CDR and FDH regularization schemes is within 0.2% for all tested kinematics.
• The model shows excellent agreement with HERA data for exclusive φ and ρ production at high virtuality.
• The infrared cutoff dependence is up to ∼5% but vanishes in the limit Q² → ∞, confirming the theoretical consistency of the approach.