TRANSVERSE SPIN EFFECTS IN SINGLE AND DOUBLE HADRON ELECTROPRODUCTION AT HERMES

In the first phase of the HERA II running period the HERMES collaboration is taking data with a transversely polarized Hydrogen target. It was installed during the HERA shutdown in the fall of 2000. The transverse target extends the spin physics program of HERMES to the topic of transversity. It allows to investigate the distribution of transversely polarized quarks in a transversely polarized nucleon. In the data evidence is found not only for a non-zero signal on transversity but also on the Sivers mechanism that can be related to non-zero orbital angular momenta of the quarks in a transversely polarized nucleon.