Single Transverse Spin Asymmetry in $p^\uparrow p \to \pi X$ and   $ep^\uparrow \to \pi X$
  Single transverse spin asymmetry for the pion production in pp and ep collisions is studied in the framework of collinear factorization. The soft-gluon pole contributions with twist-3 distribution and fragmentation functions are identified and its characteristic features are discussed. 
Yuji Koike (Niigata Univ.)