The persistent nonperturbative charm enigma

The question of the existence and possible magnitude of nonperturbative (often called intrinsic) charm in the proton has long confounded attempts to cleanly isolate such a contribution in global analyses of high-energy experiments. In this letter, we show that the available (non)perturbative QCD theory and hadronic data have still not developed to a sufficient level to clearly resolve this problem. We highlight a number of challenging aspects that must be confronted in extracting nonperturbative charm in PDF fits, and in so doing, present an updated next-to-next-to-leading order CT analysis of fitted charm, CT18 FC, which we also compare to recent studies. We outline the theory developments and future data needed to make progress on this subject. & COPY; 2023 Elsevier B.V. This is an open access article under the CC BY license (http:// creativecommons .org /licenses /by /4 .0/). Funded by SCOAP3.

Automated summary

The long-standing problem of nonperturbative charm in the proton and its magnitude in high-energy experiments remains unresolved due to the limitations of current nonperturbative QCD theory and hadronic data. In this letter, we present a next-to-next-to-leading order CT analysis, CT18 FC, which highlights the challenges in extracting nonperturbative charm in PDF fits. We also discuss the required theory developments and future data to make progress in this field.