Single-spin asymmetries in semi-inclusive pion production are measured by the HERMES experiment for the first time, with a transversely polarised hydrogen target. Two different sine-dependencies are extracted which can be related to the quark distributions transversity h_1(x) and the Sivers function f_1T^perp(x).
Comment: 4 pages, 2 figures, reference [7] updated, contribution to the proceedings for the XXXIXth Rencontres de Moriond (QCD and High Energy Hadronic Interactions), March 28th to April 4th, 2004, La Thuile, Italy