Color-octet contributions toxFdistributions inJ/ψhadroproduction at fixed target energies

We study $J/\psi$ production at fixed-target energies, including the color-octet production mechanisms predicted by NRQCD. In an earlier paper, we found that the octet components were crucial in understanding $p_T$-integrated forward ${(x}_F>0)$ cross sections. Here we make a detailed comparison of the theoretical predictions with measured $x_F$ distributions from fixed-target experiments. We find that the model predictions agree well with data. Taking into account higher orders in NRQCD, we argue that $\sigma \left({\chi }_1\right)/\sigma \left({\chi }_2\right)=0.6\mathrm{}$, in excellent agreement with data. Similiar arguments also predict that $\sigma \left(\chi \right)/\sigma (J/\psi )$ is roughly equal in photo- and hadroproduction.