We present measurements of the polarization of the $ J/psi $ produced in 800-GeV proton interactions with a copper target. Polarization of the $ J/psi $ is sensitive to the $ c bar{c} $ production and hadronization processes. A longitudinal polarization is observed at large $ x_{F} $, while at small $ x_{F} $ the state is produced essentially unpolarized or slightly transversely polarized. No significant variation of the polarization is observed versus $ p_{T} $.
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