Color-Octet $J/ψ$ Production at Low $p_\perp$

Abstract

We study contributions from color-octet quarkonium formation mechanisms to $J/ψ$ hadroproduction at low $p_\perp$. We include transitions of color-octet $c\bar{c}$ states into ``direct'' $J/ψ$ and into $χ_{1,2}$ which decay radiatively into a $J/ψ$. Together with earlier work, this calculation constitutes a complete analysis of $p_\perp$-integrated $J/ψ$ production at leading twist. We find that the leading-twist contribution is not sufficient to reproduce the observed production rates and polarization of the $J/ψ$ and $χ_{1,2}$. Hence there must exist other important quarkonium production mechanisms at low $p_\perp$.