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Measurement of Delta G / G at RHIC

RHIC will be primarily a collider for heavy ion physics; a spin physics program has been recently approved and involves the acceleration and storage of polarized proton beams and experiments with the two major detectors STAR and PHENIX. This program will run during the calibration proton runs for the heavy ion program (20 % of the running time per year).

Several measurements to access the polarized gluon and sea quark distributions are proposed. The measured asymmetries are a convolution of the unknown polarized parton distribution functions in both colliding protons with the elementary scattering asymmetry summed over the different subprocesses that contribute to the observed events. The extraction of the polarized gluon distribution is then not straight forward and adds some uncertainty to the extracted results.

To access tex2html_wrap_inline2370 the theoretically cleanest process proposed at RHIC is the prompt- tex2html_wrap_inline2248 production. In symbols this reads:


In our proposed experiment, the asymmetry for the open charm photo-production reads


Thus the extraction of tex2html_wrap_inline2370 requires different theoretical inputs in the two proposed experiments (RHIC and COMPASS), which can be regarded as complementary. In particular, to achieve good sensitivity on tex2html_wrap_inline2370 in RHIC measurements, better knowledge of polarized valence quark distribution functions is essential. The measurement of tex2html_wrap_inline2382 and tex2html_wrap_inline2384 , however, will not be accessible at RHIC from the presently proposed measurements, and will be taken from existing or forthcoming semi-inclusive deep inelastic scattering experiments, like COMPASS, where we will probe to a high accuracy also the polarized valence and sea quark distribution functions.

In the following we first describe the prompt- tex2html_wrap_inline2248 and the jet production. Then we compare the time scale and the experimental methods adopted, and finally we summarize our conclusions.

Lars Schmitt
Wed May 22 16:44:09 METDST 1996