A clear test of perturbative QCD in large-pT photoproduction

It is shown that measurement of the cross-section differences $\text{E}\text{d}\text{σ}\text{d}{}^3\text{p(γ}\text{p}\text{→}\text{h}{}^{\mathrm{+}}\text{X}\text{) ?}\text{E}\text{d}\text{σ}\text{d}{}^3\text{p (γ}\text{p}\text{→}\text{h}{}^{\mathrm{?}}\text{X}\text{)}$ at large transverse momentum provides a good test of perturbative QCD. Such differences are insensitive to the parton Fermi motion and to the poorly known sea-quark and gluon distribution functions. Moreover the hadronized photon component is shown to contribute little compared to the point-like one. Presently available photon beams at the CERN-SPS and FNAL are sufficient to test QCD in large-p_T photoproduction.