The structure functions of a real photon are calculable in QCD. The leading contribution is proportional to 1n Q2, with a coefficient reflecting the gluon flux in a real photon. We investigate this leading term for non-zero target photon mass. In an appropriate limit the gluon content in a virtual photon is found to vanish. The gluon radiative corrections of QCD can thus be turned off by tuning the target photon mass.
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One of us (T.U.) would like to thank the Humboldt foundation for financial support, and also the DESY Theory Division for its hospitality. We both extend our thanks to the CERN Theory Division, where this paper was written. We also thank G. Martinelli for adviceo n the Mellin transform inversion.
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