Large-p_T Inclusive pi^0 Cross Sections and Next-to-Leading-Order QCD Predictions

TL;DR

Problem: large-p_T pi0 production tests perturbative QCD across fixed-target and ISR energies. Approach: compute inclusive pi0 cross sections at NLO using established PDFs and FFs, analyze scale dependence with fixed and optimized scales, and contrast fixed-target with higher-energy data. Findings: shapes are reasonably captured but normalizations differ; fixed-target data require normalization factors (~1.5–2.5) depending on scales, while higher-energy data show better stability though energy dependence and fragmentation uncertainties remain; resummation of ln(1−z) in fragmentation and refined FFs are proposed to improve agreement. Significance: improved understanding of hadronic pi0 production informs prompt-photon background estimates and guides future theory developments.

Abstract

We review the phenomenology of pi^0 production at large transverse momentum in proton-induced collisions. Uncertainties in the next-to-leading-order predictions of Quantum Chromodynamics are discussed. The comparison with data reveals that the disagreement between theory and experiment lies essentially in an overall normalization factor. The situation for pi^0 production is contrasted with that of prompt-photon production in hadronic collisions.

Figures (13)

• Figure 1: Dependence on $x_T$ of experimental cross sections for inclusive prompt-photon production normalized to NLO predictions based on the MRST2 4r parton densities. The dotted vertical lines correspond to $p_T = 5$ GeV/c for the E706 and ISR experiments.
• Figure 2: Differential cross section $Ed^3\sigma/d^3p$ for the inclusive production of $\pi^0$ mesons with $p_T=7$ GeV and $|\eta|<0.75$ in the scattering of 530 GeV protons on a fixed Beryllium target, evaluated as a function of the initial-state factorization scale $M$ and the fragmentation scale $M_F$ using the MRST2 4r parton densities. The contours of constant cross section are shown in the $(M,M_F)$ plane. At each point, the renormalization scale $\mu$ is evaluated from Eq. (\ref{['2e']}).
• Figure 3: Compilation of the inclusive $\pi^0$ cross sections discussed in the text as functions of $p_T$.
• Figure 4: Comparison of WA70 11r$\pi^0$ data with NLO predictions for three different sets of parton densities and two different scale choices. The statistical and systematic errors are added in quadrature.
• Figure 5: Comparison of UA6 10r$\pi^0$ data with NLO predictions based on the MRST2 4r parton densities. Very similar results are obtained with the CTEQ4M 3r parton densities.