Charm and beauty structure of the proton

TL;DR

This paper reviews heavy quark production data from HERA, testing quantum chromodynamics and probing the gluon density in the proton through charm and beauty measurements in different scattering regimes.

Contribution

It provides a comprehensive overview of experimental results on charm and beauty production, confirming compatibility with perturbative QCD predictions and including insights from multiple collaborations.

Findings

Results agree with perturbative QCD predictions

Heavy quark production probes gluon density in the proton

Various experimental techniques effectively identify charm and beauty events

Abstract

This paper will review the data collected by the H1 and ZEUS Collaborations concerning the production of heavy quarks (charm and beauty) at the electron-proton collider HERA. Heavy quark production is an important testing ground for quantum chromodynamics (QCD), because QCD calculations are expected to be reliable if a hard scale is present in the process. In heavy quarks production a hard scale is provided by the quark mass. Moreover heavy quarks production can give direct access to the gluon density in the proton due to the fact that it proceeds, in QCD, almost exclusively via photon-gluon fusion, where a photon from the incoming electron interacts with a gluon in the proton giving an heavy quark-anti-quark pair. Results will be shown both for deep-inelastic scattering (DIS), where the virtuality of the exchanged boson Q**2 is large, and photo-production, where the Q**2 is equal to zero. Various experimental techniques are used in order to select charm and beauty events, ranging from the measurement of D* cross section to impact parameter analyses. The results are found to be compatible with the predictions of perturbative QCD. A brief summary of the open charm analyses done by the COMPASS Collaboration will be also given.