Color-Octet Fragmentation and the psi' Surplus at the Tevatron
Eric Braaten, Sean Fleming
TL;DR
It is suggested that the dominant $\psi'$ production mechanism is the fragmentation of a gluon into a $c \bar c$ pair in a pointlike color-octet S-wave state, which subsequently evolves nonperturbatively into a $\psI'$ plus light hadrons.
Abstract
The production rate of prompt $ψ'$'s at large transverse momentum at the Tevatron is larger than theoretical expectations by about a factor of 30. As a solution to this puzzle, we suggest that the dominant $ψ'$ production mechanism is the fragmentation of a gluon into a $c \bar c$ pair in a pointlike color-octet S-wave state, which subsequently evolves nonperturbatively into a $ψ'$ plus light hadrons. The contribution to the fragmentation function from this process is enhanced by a short-distance factor of $1/α_s^2$ relative to the conventional color-singlet contribution. This may compensate for the suppression by $v^4$, where $v$ is the relative momentum of the charm quark in the $ψ'$. If this is indeed the dominant production mechanism at large $p_T$, then the prompt $ψ'$'s that are observed at the Tevatron should almost always be associated with a jet of light hadrons.