First measurement of proton's charge form factor at very low $Q^2$ with   initial state radiation
  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 $0.001\leq Q^2\leq 0.004 (GeV/c)^2$. 
M. Mihovilovi\v{c}, A. B. Weber, P. Achenbach, T. Beranek, J.   Beri\v{c}i\v{c}, J. C. Bernauer, R. B\"ohm, D. Bosnar, M. Ca...
nucl-ex hep-ex