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

C. H. Leung, K. Nagai, K. Nakano, D. Nawarathne, J. Dove, S. Prasad, N. Wuerfel, C. A. Aidala, J. Arrington, C. Ayuso, C. L. Barker, C. N. Brown, W. C. Chang, A. Chen, D. C. Christian, B. P. Dannowitz, M. Daugherity, L. El Fassi, D. F. Geesaman, R. Gilman, Y. Goto, R. Guo, T. J. Hague, R. J. Holt, M. F. Hossain, D. Isenhower, E. Kinney, A. Klein, D. W. Kleinjan, Y. Kudo, P. -J. Lin, K. Liu, M. X. Liu, W. Lorenzon, R. E. McClellan, P. L. McGaughey, M. M. Medeiros, Y. Miyachi, S. Miyasaka, D. H. Morton, K. Nakahara, S. Nara, S. F. Pate, J. C. Peng, A. Pun, B. J. Ramson, P. E. Reimer, J. G. Rubin, F. Sanftl, S. Sawada, T. Sawada, M. B. C. Scott, T. -A. Shibata, A. S. Tadepalli, M. Teo, R. S. Towell, S. Uemura, S. G. Wang, A. B. Wickes, J. Wu, Z. H. Ye

Published 2024-06-17Version 1

We report the $p+p$ and $p+d$ differential cross sections measured in the SeaQuest experiment for $J/\psi$ and $\psi\left(2S\right)$ 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 $\sigma_{\psi\left(2S\right)} / \sigma_{J/\psi}$ cross section ratios are found to increase as $x_F$ increases, indicating that the $q \bar{q}$ annihilation process has larger contributions in the $\psi\left(2S\right)$ production than the $J/\psi$ production. The $\sigma_{pd}/2\sigma_{pp}$ cross section ratios are observed to be significantly different for the Drell-Yan process and $J/\psi$ production, reflecting their different production mechanisms. We find that the $\sigma_{pd}/2\sigma_{pp}$ ratios for $J/\psi$ production at the forward $x_F$ region are sensitive to the $\bar{d}/ \bar{u}$ flavor asymmetry of the proton sea, analogous to the Drell-Yan process. The transverse momentum ($p_T$) distributions for $J/\psi$ and $\psi\left(2S\right)$ production are also presented and compared with data collected at higher center-of-mass energies.