Higher Twist Effects in Parton Fragmentation Functions
  We study twist expansions for parton fragmentation functions based on the definition of the twist as an invariant matrix element of a light-cone, bilocal operator. The results are then applied to a method which might be used to extract higher twist effects in the fragmentation sector using both $e^+ e^-$, and $e^- p$ collisions. We discuss how to apply the later measurements to experiments at the Jefferson National Acceleration Facility. 
Guanghua Xu, Ed V. Hungerford, and Larry Pinsky