A Possible Fixed Target Programme for the Polarized HERA Proton Ring

The physics programme for a possible fixed target polarized nucleon-nucleon collision experiment aiming at studying the nucleon spin structure at HERA is described. The experiment named HERA-N could be realized using an internal polarized gas target in the HERA polarized/unpolarized proton beam. Single spin asymmetry measurements could provide unique information on higher twist contributions. Once the HERA proton beam is polarized measurements of the polarized gluon distribution using double longitudinal spin asymmetries in both photon and J/psi production appear possible. A study of the Drell-Yan process for different relative orientation of beam and target polarization can provide information on a variety of still not or badly measured polarized structure functions. The experiment would constitute a fixed target complement to the RHIC spin physics program with competitive statistical accuracy.