Color-octetψ′production at lowp⊥

We study contributions from color-octet quarkonium formation mechanisms to ${\mathit{p}}_{\mathrm{\perp }}$-integrated ${\mathrm{\psi }}^{\prime }$ production cross sections in pion-nucleon reactions. The observed polarization of the ${\mathrm{\psi }}^{\prime }$ is not reproduced by calculations where leading-order, leading-twist QQ¯ production mechanisms are combined with the color-singlet and color-octet mechanisms of bound state formation. This shows that there are other important quarkonium production mechanisms at low ${\mathit{p}}_{\mathrm{\perp }}$. © 1996 The American Physical Society.