6533b856fe1ef96bd12b355e

RESEARCH PRODUCT

Leading order corrections to the Bethe-Heitler process in the γp→l+l−p reaction

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The ratio of dilepton production cross sections on a proton, using the γp→l+l−p process, above and below the dimuon production threshold allows one to extract the effective lepton-proton interaction, which is required to be identical for electrons and muons if lepton universality is exact. To test for a scenario of broken universality at the percent level, of the size that could explain the different proton charge radii extracted from electron scattering and from muonic hydrogen spectroscopy, we evaluate all one-loop QED corrections to this process, including the full lepton mass dependencies. We furthermore show that two photon–exchange processes with both photons attached to the proton line vanish after averaging over dilepton angles and estimate the relatively small radiation off the proton. We compare the full one-loop calculation with a soft-photon approximation of the same order and present estimates for a planned experiment.