On the Physics Potential of Polarized Nucleon-Nucleon Collisions at HERA

The physics of polarized nucleon–nucleon collisions originating from an internal polarized target in the HERA proton beam is investigated. Based on 240 pb − 1 integrated luminosity at 40 GeV c.m. energy, statistical sensitivities are given over a wide ( x F , p T )–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 p T -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 ≤ x gluon ≤ 0.4 with a good statistical accuracy.