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The question of the 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. We introduce physics concepts and terminology to rigorously discuss determination of nonperturbative charm by fitting parton distribution functions (PDFs) in the framework of perturbative QCD. We then review connections of the thus fitted charm parametrization to the meson-baryon and other nonperturbative models of the intrinsic charm. Following this discussion, we compare a newly published next-to-next-to-leading order CTEQ-TEA determination of fitted charm PDF, CT18 FC, to the recent NNPDF analysis and other studies. We demonstrate that there is not enough evidence yet in the CT or NNPDF analysis to establish existence of the intrinsic charm, even though fitted charm may marginally improve the description of observations. Future experiments at the LHC and EIC, combined with lattice QCD calculations, have the potential to elucidate the issue. Based on arXiv:2211.01387, 1707.00657, and 2205.10444.
Webinar at https://us02web.zoom.us/j/81572103194?pwd=eE1QVWZFc1hWbWszZ2N0RW1iWHFBZz09