Tim Hobbs - ANL - TITLE: The once and future challenge of the proton's charm content


As the lightest of the heavy flavors, the charm quark occupies a liminal space in QCD, transgressing the boundary separating perturbative and nonperturbative dynamics. For this reason, charm plays a central role in efforts to refine QCD and our corresponding understanding of proton structure for experiments at the LHC. In this talk I provide an overview of these issues, illustrating subtleties in the treatment of heavy flavors in perturbative QCD analyses. Within this context, I outline a stubborn problem in the theory of nucleon structure: the open question of whether the proton contains a significant nonperturbative (often called "intrinsic") charm component. I discuss some of the theoretical ambiguities that have kept this challenge alive while summarizing the findings of a recent analysis implying the need for more data --- for instance, from the Electron-Ion Collider --- to resolve this question.


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