Abstract
Systematic differences in the the proton’s charge radius, as determined by ordinary atoms and muonic atoms, have caused a resurgence of interest in elastic lepton scattering measurements. The proton’s charge radius, defined as the slope of the charge form factor at Q\(^2\) = 0, does not depend on the probe. Any difference in the apparent size of the proton, when determined from ordinary versus muonic hydrogen, could point to new physics or need for the higher order corrections. While recent measurements seem to now be in agreement, there is to date no high precision elastic scattering data with both electrons and positrons. A high precision proton radius measurement could be performed in Hall B at Jefferson Lab with a positron beam and the calorimeter based setup of the PRad experiment. This measurement could also be extended to deuterons where a similar discrepancy has been observed between the muonic and electronic determination of deuteron charge radius. A new, high precision measurement with positrons, when viewed alongside electron scattering measurements and the forthcoming MUSE muon scattering measurement, could help provide new insights into the origins of the proton radius puzzle, and also provide new experimental constraints on radiative correction calculations.
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Data Availability Statement
This manuscript has no associated data or the data will not be deposited. [Authors’ comment: This article discusses a potential experiment that could be done if a positron source were to be constructed at JLab. As this experiment is only hypothetical at the moment, there is no data to deposit.]
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Acknowledgements
This work is supported in part by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-FG02-03ER41231 and DE-AC05-060R23177. This work is supported in part by NSF Grant NSF PHY-1812421.
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Hague, T.J., Dutta, D., Higinbotham, D.W. et al. Elastic positron–proton scattering at low Q\(^2\). Eur. Phys. J. A 57, 199 (2021). https://doi.org/10.1140/epja/s10050-021-00508-6
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DOI: https://doi.org/10.1140/epja/s10050-021-00508-6