We study the possibility of intrinsic (non-perturbative) charm in parton distribution functions (PDF) of the proton, within the context of the CT10 next-to-next-to-leading order (NNLO) global analysis. Three models for the intrinsic charm (IC) quark content are compared: (i) $hat{c}(x) = 0$ (zero-IC model); (ii) $hat{c}(x)$ is parametrized by a valence-like parton distribution (BHPS model); (iii) $hat{c}(x)$ is parametrized by a sea-like parton distribution (SEA model). In these models, the intrinsic charm content, $hat{c}(x)$, is included in the charm PDF at the matching scale $Q_c=m_c=1.3$ GeV. The best fits to data are constructed and compared. Correlations between the value of $m_c$ and the amount of IC are also considered.
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