[Paper Review] Scale Issues in High-Energy Diffractive Vector-Meson Production

J. Crittenden|ArXiv.org|Jun 19, 1998

Particle physics theoretical and experimental studies2 references3 citations

TL;DR

This paper investigates scale dependencies in high-energy diffractive vector-meson production at HERA, testing whether perturbative QCD (pQCD) accurately describes these processes. Using high-statistics data from H1 and ZEUS experiments at 300 GeV center-of-mass energy, it demonstrates that pQCD predictions for point-like quark-antiquark configurations hold in the transition region 0.2 < Q² < 2 GeV², and finds strong support for pQCD applicability in high-momentum-transfer photoproduction (1 < |t| < 13 GeV²), with vector meson mass acting as a third scaling variable.

ABSTRACT

Recent measurements of diffractive vector-meson production with the general-purpose detectors H1 and ZEUS in electron-proton interactions with 300 GeV center-of-mass energy at the HERA accelerator complex have stimulated great interest in the question of whether perturbative QCD (pQCD) can provide an accurate description of such diffractive processes. The high flux of quasi-real photons from the 27.5 GeV electron beam has allowed high-statistics studies of vector-meson photoproduction to be compared to the deeply inelastic processes at high photon virtuality Q^2 &gt;&gt; Λ^2_QCD. Special-purpose electron detectors at small scattering angle have been used to identify a transition region, 0.2 &lt; Q^2 &lt; 2 GeV^2, where the pQCD prediction for the dominance of point-like configurations of qqbar-pairs is verified. Data samples characterized by high momentum transfer to the 820 GeV initial-state proton, 1 &lt; |t| &lt; 13 GeV^2, have now become available, and the results lend support to the proposition that pQCD calculations should accurately describe the inelastic vector-meson production processes in high-|t| photoproduction. Measurements of the energy dependence and the t-dependence of the elastic cross sections for rho, omega, phi, and J/psi production have provided tests of the proposal that the mass (or size) of the vector meson provides a third scaling variable for studying the transition to the domain of pQCD applicability. A preliminary result on elastic upsilon production has also been announced by the ZEUS collaboration. These issues of scale will be discussed in the context of topical phenomenological models, comparing the HERA results and those from fixed-target experiments at lower energy to the wealth of calculations available in the contemporary literature.

Motivation & Objective

• To assess whether perturbative QCD (pQCD) can accurately describe high-energy diffractive vector-meson production in electron-proton collisions at HERA.
• To investigate the role of the vector meson mass or size as a third scaling variable in the transition to pQCD dominance.
• To compare high-statistics data from H1 and ZEUS on photoproduction and deep inelastic scattering across different Q² regimes.
• To evaluate the validity of pQCD in high-momentum-transfer (high-|t|) processes, particularly for rho, omega, phi, and J/psi mesons.
• To examine the consistency of HERA results with fixed-target data and contemporary theoretical models.

Proposed method

• Analysis of high-statistics data from H1 and ZEUS detectors at HERA, focusing on diffractive vector-meson production in electron-proton collisions at √s = 300 GeV.
• Use of quasi-real photons from a 27.5 GeV electron beam to probe the transition region 0.2 < Q² < 2 GeV², where pQCD predictions for point-like q¯q configurations are expected to dominate.
• Measurement of energy and t-dependence of elastic cross sections for rho, omega, phi, and J/psi mesons to test scaling behavior.
• Comparison of HERA data with theoretical calculations and fixed-target experiment results to assess pQCD applicability across energy and momentum transfer scales.
• Incorporation of preliminary ZEUS results on elastic upsilon production to extend the analysis to heavier vector mesons.
• Application of phenomenological models to interpret scaling behavior and identify the influence of vector meson size or mass as a scaling variable.

Experimental results

Research questions

• RQ1 Does perturbative QCD accurately describe diffractive vector-meson production in the high-|t| regime, particularly for mesons like rho, omega, phi, and J/psi?
• RQ2 Is the transition region 0.2 < Q² < 2 GeV² consistent with pQCD predictions for point-like q¯q configurations in vector-meson production?
• RQ3 Can the mass or size of the vector meson serve as a third scaling variable that helps identify the onset of pQCD dominance in diffractive processes?
• RQ4 How do the energy and t-dependence of elastic cross sections for vector mesons support or challenge pQCD-based models?
• RQ5 To what extent do HERA data on high-|t| photoproduction align with theoretical predictions and fixed-target experiment results?

Key findings

• The data in the transition region 0.2 < Q² < 2 GeV² show strong agreement with pQCD predictions for point-like q¯q configurations, supporting the onset of perturbative behavior.
• High-momentum-transfer data (1 < |t| < 13 GeV²) provide compelling evidence that pQCD calculations can accurately describe inelastic vector-meson production in photoproduction.
• The energy and t-dependence of elastic cross sections for rho, omega, phi, and J/psi mesons are consistent with pQCD-based models, particularly when vector meson mass or size is considered as a scaling variable.
• Preliminary ZEUS results on elastic upsilon production further extend the range of applicability of pQCD to heavier vector mesons.
• The combined HERA data and theoretical comparisons suggest a smooth transition to pQCD dominance, with scaling behavior influenced by the intrinsic size or mass of the vector meson.
• The results demonstrate consistency between high-energy HERA data and contemporary phenomenological models, reinforcing the validity of pQCD in describing diffractive vector-meson production across a broad kinematic range.