  A new debate has recently arisen on the subject of orbital angular momentum
in QCD, in particular on its observability and on its partonic interpretation.
Orbital momentum can be defined in QCD using two different decomposition
schemes that yield a kinetic and a canonical definition, respectively. We argue
that kinetic orbital angular momentum is intrinsically associated with twist
three generalized parton distributions, and it is therefore more readily
observable, while, due to parity constraints, canonical angular momentum, if
defined as suggested in the literature in terms of generalized transverse
momentum distributions, cannot be observed in scattering processes involving a
single hadronic reaction plane.
