Hadroproduction of Charmonium at Large $x_F$

We present a higher-twist production mechanism for $η_c$ and $χ_J$ charmonium at large momentum fraction $x_F$ in pion-nucleon collisions. The higher-twist contribution is essentially independent of $x_F$ and therefore becomes dominant at large $x_F$, where the leading-twist contribution falls off as $(1-x_F)^3$. We show that the higher-twist mechanism produces longitudinally polarized $χ_1$ and $χ_2$. For the $χ_2$, this is clearly different from the leading-twist prediction of transverse polarization. For the $χ_1$, the polarization of the leading- and higher-twist contributions is qualitatively similar.

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