Measurement of the Transverse Single‐Spin Asymmetry in $J/\psi$

We report an update on our ongoing extraction of the transverse single‐spin asymmetry (A_{N}) in the (J/psi omu^{+}mu^{-}) channel from the Fermilab E1039 SpinQuest experiment. Preliminary data were collected with a 120,GeV unpolarized proton beam incident on a transversely polarized solid NH(_3)/ND(_3) target. In the Collins–Soper frame, raw left–right asymmetries are being extracted via the cross‐ratio method. We present early asymmetry measurements in different mass regions and future SpinQuest data will report on improved $A_N$ as functions of Feynman-(x) and transverse momentum (q_{T}). We discuss work in progress to evaluate systematic uncertainties and to introduce relative luminosity, polarization, dilution‐factor, and packing‐fraction corrections in the future. These studies along with Monte Carlo cross checks will eventually guide the final physics extraction and global analyses of the Sivers function.