39 3 v 1 2 1 A ug 1 99 6 August 1996 DESY 96 – 128 INFNCA – TH 9616 hep – ph 9608 xxx On the Physics Potential of Polarized Nucleon – Nucleon Collisions at HERA 1

The physics of polarized nucleon–nucleon collisions originating from an internal polarized target in the HERA proton beam is investigated. Based on 240 pb integrated luminosity at 40 GeV c.m. energy, statistical sensitivities are given over a wide (xF , pT )–range for a variety of inclusive and exclusive final states. By measuring single spin asymmetries unique information can be obtained on higher twist contributions and their pT -dependence. From double spin asymmetries in both photon and J/ψ production it appears possible to measure the polarized gluon distribution in the range 0.1 ≤ xgluon ≤ 0.4 with a good statistical accuracy. Contribution to the Proceedings of the Workshop on ‘Future Physics at HERA’, DESY–Hamburg, Oct. 1995 May 1996 e-mail: [email protected]