Fixed-target charmonium production and pion parton distributions

We investigate how charmonium hadroproduction at fixed-target energies can be used to constrain the gluon distribution in pions. Using nonrelativistic QCD (NRQCD) formulation, the J/psi and psi(2S) cross sections as a function of longitudinal momentum fraction xF from pions and protons colliding with light targets, as well as the psi(2S) to J/psi cross section ratios, are included in the analysis. The color-octet longdistance matrix elements are found to have a pronounced dependence on the pion parton distribution functions (PDFs). This study shows that the xF differential cross sections of pion-induced charmonium production impose strong constraints on the pion's quark and gluon PDFs. In particular, the pion PDFs with larger gluon densities provide a significantly better description of the data. It is also found that the production of the psi(2S) state is associated with a larger quark-antiquark contribution, compared with J/psi.

Automated summary

In this study, we investigate how the production of charmonium quark pairs at fixed-target energies can be used to constrain the gluon distribution in pions. The results show that the differential cross sections of pion-induced charmonium production with different longitudinal momentum fractions xF impose strong constraints on the quark and gluon probability distribution functions of the pion. It is found that pions with higher gluon densities provide a better description of the data. Furthermore, the production of the psi(2S) state is associated with a larger contribution from quark-antiquark pairs compared to J/psi.