Higher twist contributions from the direct pion coupling in e⁺e^- annihilation, photoproduction and π^-p Drell-Yan

We present calculations of normalized higher twist contributions in three processes in which the central sub-processes are related by crossing: the production of hadrons at high transverse momentum relative to the thrust axis in e⁺e^- annihilation, photoproduction of high transverse momentum pions from a proton target, and high transverse momentum lepton pair production in π^-p collisions. The last of these is most interesting, not only because the higher twist contribution is significant, but also the QCD interpretation of the data is uncertain.