Photoproduction of Massive Muon Pairs at High Energies

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Abstract
We study the high-energy photoproduction of massive muon pairs off protons in the framework of a field-theoretical parton model. Parton annihilation is found to contribute to the production of high-mass symmetric pairs. This contribution is important for events where a substantial fraction of the incident photon's momentum appears in the hadronic final state. It may be separated from the large background of Bethe-Heitler muon pairs by measuring a cross section differential in the longitudinal momentum of the muons. We derive a scaling law for the parton-annihilation contribution, showing that the cross section measures the as yet unexplored structure function of the photon. Other mechanisms of muon pair production are discussed and shown to be negligible in the region where the parton effect is important. Finally, we show that the parton contribution is observable despite the experimental complication of integrating the cross section over a bremsstrahlung-photon spectrum.