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

TL;DR

This study measures $J/ar{psi}$ and $ar{psi}(2S)$ production cross sections in proton-proton and proton-deuteron interactions at 120 GeV, comparing results with theoretical models and exploring production mechanisms and flavor asymmetries.

Contribution

First measurement of charmonium production cross sections at 120 GeV in $p+p$ and $p+d$ interactions, with analysis of production ratios and flavor asymmetry effects.

Findings

Cross sections agree with NRQCD predictions.

The $ar{psi}(2S)/J/ar{psi}$ ratio increases with $x_F$.

Deuteron-proton ratios reveal flavor asymmetry sensitivity.

Abstract

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.