Comments on Cahn and Sivers effects in SIDIS

Abstract

The role of intrinsic $k_{\perp }$ in semi-inclusive Deep Inelastic Scattering (SIDIS) processes ($\ell p\to \ell hX$) is studied within QCD parton model at leading order. The resulting picture is applied to the description of the weighted single spin asymmetry $A_{UL}^{\sin {\varphi }_h}$ measured by HERMES. It is shown that these data could be described by the Sivers mechanism alone. However, the extracted Sivers functions fail to describe the HERMES data on $A_{UT}^{\sin ({\varphi }_h-{\varphi }_S)}$.

Comments: Latex 2e, 4 pages, 5 figures, talk delivered by A. Prokudin at the ``16th International Spin Physics Symposium'', SPIN2004, October 10-16, 2004, Trieste, Italy