Predictions for single spin asymmetries in $\ell p^{\uparrow} \to \pi X$ and $\gamma^* p^{\uparrow} \to \pi X$

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 $\vec k_\perp$ 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 $p^\uparrow p \to \pi X$ , and by assuming that the QCD factorization theorem holds also when transverse momenta are taken into account. The predictions given here are based on the assumption that the Collins effect is the only cause of the observed single spin asymmetries in $p^\uparrow p \to \pi X$ . Eventual spin and $\vec k_\perp$ dependences in the quark distribution functions, the so-called Sivers effect, are also discussed.