Hadroproduction of charmonium at large xF.

Abstract

We present a higher-twist production mechanism for $\eta_c$ and $\chi_J$ 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 $\chi_1$ and $\chi_2$. For the $\chi_2$, this is clearly different from the leading-twist prediction of transverse polarization. For the $\chi_1$, the polarization of the leading- and higher-twist contributions is qualitatively similar.