First measurement of proton's charge form factor at very low $Q^2$ with initial state radiation

Abstract

We report on a new experimental method based on initial-state radiation (ISR) in e-p scattering, in which the radiative tail of the elastic e-p peak contains information on the proton charge form factor ($G_E^p$) at extremely small $Q^2$. The ISR technique was validated in a dedicated experiment using the spectrometers of the A1-Collaboration at the Mainz Microtron (MAMI). This provided first measurements of $G_E^p$ for $0.001\le Q^2\le 0.004(GeV/c{)}^2$.

arXiv comment6 pages, 3 figures

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• Low-Energy Lepton-Proton Bremsstrahlung via Effective Field Theory
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