First Monte Carlo global QCD analysis of pion parton distributions*

In this work, we determined the parton distribution function (PDF) of the pion. Previously, its PDF has been determined only by Drell-Yan (DY) experiments such as E615 and NA10 which only constrain the high momentum fraction region and the valence distribution. In the DY process, two hadrons collide, with one donating a quark and the other donating an antiquark, producing a dimuon pair. For lower momentum fractions, data was included from leading neutron (LN) electroproduction experiments such as H1 and Zeus done at HERA. An electron strikes a target proton, which transforms into a neutron. This process is dominated by the one-pion exchange. These data provide previously unseen constraints on sea quark and gluon PDFs. The PDFs we obtain reveal that at the input scale, the gluon carries a significant fraction of the pion momentum ∼30%, higher than predicted with only the DY data, and the sea carries ∼15% of the momentum fraction of the pion. We can also describe the dbar-ubar asymmetry in the proton using this pion PDF.