Heavy quark photoproduction at THERA

Heavy quark production can provide information on the structure of the real photon as well as provide stringent tests of QCD by itself. In this paper the potential of the possible future ep collider, THERA, to give new information on the real photon structure through charm and beauty quark photoproduction is studied. The potential of the collider is also compared with other existing or planned colliders. Photoproduction processes are dominated by the exchange of quasi-real photons (virtuality of the photon Q ≪ 1GeV). Their energy distribution can be described by an effective (real) photon energy spectrum, i.e. using the Weizsäcker-Williams approximation. A hard scale is provided by a large transverse momentum or the mass of the produced heavy quark Q. In this paper the region pT ≥ mQ is studied. In LO QCD, two processes contribute to the photoproduction of heavy quarks: the direct process, in which the photon couples directly to a parton in the proton, and the resolved process, in which the photon acts as a source of partons, one of which scatters from a parton in the proton. Heavy quarks can be produced in the final state or they already exist in the initial state as partons in the photon and proton, depending on the scheme used in the calculations. If not stated otherwise the computations were performed with the THERA electron and proton beams energies of 250 GeV and 920 GeV, respectively. In the first section results are presented on LO QCD calculations of inclusive charm quark production, ep → c/c̄ X, at the THERA collider. In particular the possible information this process can reveal on the structure of the photon is discussed. The second section uses MC expectations to investigate events where at least one heavy quark and two jets are produced. Further requirements on a final state muon from a semi-leptonic decay are also imposed and sensitivity to current parametrisations of the photon investigated.