Preliminary results of a new determination of the rms charge radius of the proton

New absolute and relative cross sections for elastic scattering of electrons from the proton have been measured using the linac facilities at NIST. The data were obtained using a high-pressure, flowing-gas target cell alternately filled with H 2 and CH 4 gas. The measurements span a momentum transfer range from 0.22 to 0.73 fm −1 . These new results have been combined with an extensive set of existing elastic electron scattering data in a Fourier-Bessel analysis to obtain the charge density parameters and the rms radius of the proton. Some selection among the available data was necessary because of inconsistencies between published data sets. We obtain an rms radius of 0.865 ±0.020 fm.