PHYSICS WITH POLARIZED PROTON AND ELECTRON COLLISIONS AT HERA

We describe here some possible measurements at the HERA collider in th e scenario where both the electron and the proton beam are polarized. The proposed experiments have been studied during the recent workshop on Future Physics at HERA in the dedicated working group ''polarized p rotons and electrons''. The measurement of the polarized gluon distrib ution function Delta G(x,Q(2)) from photon-gluon fusion processes in e lectron-proton deep inelastic scattering producing two jets has been i nvestigated. The size of the expected spin asymmetry and corresponding statistical uncertainties have been estimated. The results show that the asymmetry can reach a few percent, and is not washed out by hadron ization and higher order processes. Estimates of possible data on spin dependent asymmetries in inclusive deep inelastic (e) over right arro w (p) over right arrow scattering are presented. By accessing a new ki nematic domain in x and Q(2) these data would shed light on the behavi our of the polarized structure function of the proton g(1)(p) at low x and high Q(2). They would reduce substantially the uncertainty on the determination of the polarized gluon distribution Delta G(x,Q(2)) fro m QCD evolution equations. Finally, the spin asymmetries from charged current events allow to measure the spin dependent structure function g(5) which is related to the polarized distribution functions. The cha rged current reactions allow to distinguish quark and antiquark flavou rs. These measurements would provide data on Delta u(v) and Delta d(v) at high x and high Q(2) complementary to the fixed target data, with a very good statistical precision. In addition, semi inclusive D-produ ction events could give a good signal for the determination of Delta s and Delta (s) over bar.