Predictions for single spin asymmetries in lepton + p(transv. polarized) -> pion + X and gamma^* + p(transv. polarized) -> pion + X

Abstract

Predictions for the single transverse spin asymmetry A_N in semi-inclusive DIS processes are given; non negligible values of A_N may arise from spin effects in the fragmentation of a polarized quark into a final hadron with a transverse momentum k_T with respect to the jet axis, the so-called Collins effect. The elementary single spin asymmetry of the fragmenting quark has been fixed in a previous paper, by fitting data on p(transv. polarized) + P -> pion + X, and the predictions given here are uniquely based on the assumption that the Collins effect is the only cause of the observed single spin asymmetries in p(transv. polarized) + p -> pion + X. Eventual spin and k_T dependences in quark distribution functions, the so-called Sivers effect, are also discussed.