Color-Octet ${\psi }^{\mathrm{\prime }}$ Production at Low $p_{\perp }$

We study contributions from color-octet quarkonium formation mechanisms to $p_{\perp }$-integrated ${\psi }^{\mathrm{\prime }}$ production cross sections in pion-nucleon reactions. The observed polarization of the ${\psi }^{\mathrm{\prime }}$ is not reproduced by the lowest-order leading-twist color-singlet and color-octet mechanisms. This suggests that there are important quarkonium production mechanisms beyond leading twist.