An extended study of the prompt photon photoproduction at HERA with $k_T$-factorization

TL;DR

This paper analyzes prompt photon production at HERA using the $k_T$-factorization approach, incorporating higher-order subprocesses and box contributions, and finds good agreement with experimental data.

Contribution

It introduces a comprehensive $k_T$-factorization calculation including ${ m O}(\alpha^2\alpha_s^2)$ box diagrams and unintegrated parton densities, improving previous models.

Findings

Predictions agree well with H1 and ZEUS data.

Box contributions are significant, up to 15% of total cross section.

The approach effectively describes inclusive and jet-associated prompt photon production.

Abstract

We reconsider the prompt photon photoproduction at HERA in the framework of the $k_T$-factorization QCD approach. The proposed method is based on the ${\cal O}(\alpha^2\alpha_s)$ amplitudes for $\gamma q\to\gamma gq$ and $\gamma g^*\to\gamma q\bar q$ partonic subprocesses. Additionally, we take into account the ${\cal O}(\alpha^2\alpha_s^2)$ box contributions $\gamma g\to\gamma g$ to the production cross sections. The unintegrated (or transverse momentum dependent) parton densities in the proton are determined using Kimber-Martin-Ryskin (KMR) prescription. Our consideration covers both inclusive and jet associated prompt photon photoproduction rates. We find that our numerical predictions agree well with the recent data taken by H1 and ZEUS collaborations at HERA. We demonstrate that the box contributions are sizeable and amount up to $\sim15%$ of the calculated total cross section.