  We study the process of electron-positron annihilation into back-to-back
jets, where in each jet a pair of hadrons is detected. The orientation of these
two pairs with respect to each other can be used to extract the interference
fragmentation functions in a clean way, for instance from BELLE or BABAR
experiment data. This is of relevance for studies of the transversity
distribution function.
  In particular, we focus on two azimuthal asymmetries. The first one has
already been studied by Artru and Collins, but is now expressed in terms of
interference fragmentation functions. The second asymmetry is new and involves
a function that is related to longitudinal jet handedness. This asymmetry
offers a different way of studying handedness correlations.
