a Measurement of the Root Mean Square Proton Charge Radius by Muon-Proton Elastic Scattering in the Extremely Low Momentum Transfer Squared Region.

The muon-proton elastic scattering differential cross section was measured at four values of the momentum transfer squared between 0.03 F('-2) and 0.24 F('-2). These values of q('2) included some of the lowest ever attained in lepton-proton scattering. The electric form factors were calculated; the maximum systematic error of these form factors was 0.25%. A least squares fit of the electric form factors yielded a root mean square charge radius of the proton of 1.13 (+OR-) 0.21 F. *Research supported by the National Science Foundation. NSF PHY 79-00302.