Electron-proton elastic scattering cross sections were measured at low four-momentum transfers squared ( q 2 from 0.13 to 2.15 fm −2 ) at six different energies between 150 and 275 MeV. The electric ( G E ) and magnetic ( G M ) form factors of the proton have been determined by Rosenbluth plots and independently by using analytical functions for the form factors to fit the cross sections. The electric form factor is found to deviate significantly from the dipole fit. From the slope of the form factor functions at q 2 = 0 the rms radii of the charge and the magnetic moment distribution were determined. The charge rms radius is found to be more than 10% larger than the value given by the dipole fit.
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The 300 MeV electron linear accelerator of Mainz has been used to measure the angular dependence of the electron-proton elastic scattering cross sections at seven different energies for squared four-momentum transfers between 0.13 and 4.7 fm −2 . The proton form factors have been extracted from the cross sections by means of Rosenbluth plots and by fitting parametrized analytical functions directly to the cross sections. The best fit is compared to the data of other laboratories. The previously reported deviations from the dipole fit have been confirmed. From the form factors at q 2 <0.9 fm 2 the proton r.m.s. radius has been determined. A determination of the spectral function of the nucleon isovector form factor G E V in the time-like is obtained using a realistic ϱ resonance.
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The Sigma^- mean squared charge radius has been measured in the space-like Q^2 range 0.035-0.105 GeV^2/c^2 by elastic scattering of a Sigma^- beam off atomic electrons. The measurement was performed with the SELEX (E781) spectrometer using the Fermilab hyperon beam at a mean energy of 610 GeV/c. We obtain <r^2> = (0.61 +/- 0.12 (stat.) +/- 0.09 (syst.)) fm^2. The proton and pi^- charge radii were measured as well and are consistent with results of other experiments. Our result agrees with the recently measured strong interaction radius of the Sigma^-.
Total systematic errors are given.
Exclusive electroproduction of pi0 mesons on protons in the backward hemisphere has been studied at Q**2 = 1.0 GeV**2 by detecting protons in the forward direction in coincidence with scattered electrons from the 4 GeV electron beam in Jefferson Lab's Hall A. The data span the range of the total (gamma* p) center-of-mass energy W from the pion production threshold to W = 2.0 GeV. The differential cross sections sigma_T+epsilon*sigma_L, sigma_TL, and sigma_TT were separated from the azimuthal distribution and are presented together with the MAID and SAID parametrizations.
Cross section SIG(T) + EPSILON*SIG(L) for COS(THETA*) = -0.975.
Cross section SIG(T) + EPSILON*SIG(L) for COS(THETA*) = -0.925.
Cross section SIG(T) + EPSILON*SIG(L) for COS(THETA*) = -0.875.
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