Recent investigations of QCD at HERA

TL;DR

This paper reviews recent high-precision QCD measurements at HERA, comparing experimental data with theoretical models, exploring new processes, and investigating regions where perturbative QCD may not fully describe the data.

Contribution

It presents new measurements and analyses of QCD processes at HERA, including high-precision determinations of the strong coupling and heavy-quark masses, and explores factorisation in diffraction.

Findings

High-precision extraction of the strong coupling constant up to NNLO.

Combined heavy-quark cross sections used to determine charm and beauty quark masses.

First measurements of prompt photon production in diffractive photoproduction.

Abstract

The latest results from the H1 and ZEUS collaborations which challenge the QCD description of high energy $ep$ collisions are presented. Data from HERA continue to provide precision measurements and are compared to the latest theoretical predictions. Measurements of new processes are also presented as well as investigation of regions where perturbative QCD fails to describe the data. Four themes are presented here. Measurements of hard QCD processes, prompt photon and jet production, are used to compare to the latest theoretical predictions and, in the case of jet production, used to make high-precision extractions of the strong coupling constant up to next-next-to-leading order in QCD. All H1 and ZEUS charm and beauty cross sections in deep inelastic scattering have been combined and used to extract heavy-quark masses, including the running of the charm-quark mass with the scale of the process. Factorisation in diffraction has been investigated in charm production in deep inelastic scattering and prompt photon production in diffractive photoproduction has been measured for the first time. Finally, the inclusive data on deep inelastic scattering is presented in various forms in order to allow investigation of the underlying mechanism at very low photon virtuality $Q^2$ and low Bjorken $x$.