The measurement of double spin asymmetries
in certain final states seems to be the most valuable tool to measure
polarized gluon and quark distribution
functions in the nucleon. The most accurate way to do so
is the study of those processes which can be calculated
in the framework of perturbative QCD.
Production of direct photon (plus jet),
J/
(plus jet), and Drell-Yan pair final states
are most suited because there are only small uncertainties due to
fragmentation.
In the following we discuss the capabilities of
HERA-
, operated in doubly polarized mode,
to perform such measurements.
Measurement