Pion PDFs confronted by fixed-target charmonium production

The pion, as the Goldstone boson of the strong interaction, is the lightest QCD bound state and responsible for the long-range nucleon-nucleon interaction inside the nucleus. Our knowledge on the pion partonic structure is limited by the existing Drell-Yan data which are primarily sensitive to the pion valence-quark distributions. The recent progress of global analysis of pion’s parton distribution functions (PDFs) utilizing various experimental approaches are introduced. From comparisons between the pion-induced J/ ψ and ψ(2 S) production data with theoretical calculations using the CEM and NRQCD models, we show how these charmonium production data could provide useful constraints on the pion PDFs.