Measurement of J/ψ and ψ(2S) production in p + p and p + d interactions at 120 GeV

We report the p + p and p + d differential cross sections measured in the SeaQuest experiment for J/ψ and ψ (2S ) production at 120 GeV beam energy covering the forward x-Feynman (x F ) range of 0.5 < x F < 0.9.The measured cross sections are in good agreement with theoretical calculations based on the nonrelativistic QCD (NRQCD) using the long-distance matrix elements deduced from a recent global analysis of proton-and pion-induced charmonium production data.The σ ψ(2S ) /σ J/ψ cross section ratios are found to increase as x F increases, indicating that the q q annihilation process has larger contributions in the ψ (2S ) production than the J/ψ production.The σ pd /2σ pp cross section ratios are observed to be significantly different for the Drell-Yan process and J/ψ production, reflecting their different production mechanisms.We find that the σ pd /2σ pp ratios for J/ψ production at the forward x F region are sensitive to the d/ū flavor asymmetry of the proton sea, analogous to the Drell-Yan process.The transverse momentum (p T ) distributions for J/ψ and ψ (2S ) production are also presented and compared with data collected at higher center-of-mass energies.