Measurement of charmonium production in $p + p$ and $p + d$ interaction in the Fermilab SeaQuest experiment

SeaQuest has measured dimuon events from the interaction of 120 GeV proton beam on liquid hydrogen and deuterium targets with dimuon mass between 2 and 8 GeV. These dimuon events contain both the Drell-Yan process and the charmonium ($J/\psi$ and $\psi^\prime$) production. Unlike the Drell-Yan process which probes the antiquark distributions in the nucleons, the charmonium production is sensitive to both quark and gluon distributions. SeaQuest has extracted the $(p+d)/(p+p)$ cross section ratios as well as the differential cross sections for charmonium production in the kinematic region of $0.4 < x_F < 0.9$. The $(p+d)/(p+p)$ cross section ratios for charmonium production are found to be significantly different from that of the Drell-Yan process. The measured differential cross sections for charmonium production are compared with theoretical model calculations. The beam energy dependence of the charmonium production cross sections will also be presented.