Azimuthal dependence of semi-inclusive deep-inelastic reactions in the parton model

The parton model predicts that the coefficient of the terms dependent on the azimuthal angle in single-particle semi-inclusive deep-inelastic electroproduction should vanish asymptotically. This appears to be confirmed by experiment. In the light of this, we suggest that it may be possible to observe a significant azimuthal dependence in three similar reactions: two-particle semi-inclusive deep electron-positron annihilation, two-particle semi-inclusive deep-inelastic electroprodution, and single-particle semi-inclusive deep-inelastic electroproduction off a polarized target (without necessarily using a polarized beam).