The scattering of 139.5-Mev electrons in hydrogen gas at one-atmosphere pressure has been investigated using photographic emulsions. The beam of electrons from the Stanford Mark III linear accelerator, collimated to a diameter of 116 in., passed through the gas and was collected in a lead Faraday cup. Ilford C−2 emulsions, 50 μ thick, which were arranged symmetrically about the beam, detected the recoil protons. Measurements of the recoil angle γ and the range in the emulsion were made on the proton tracks. Only those events were accepted whose measured range and angle correlated within ±2.33 standard deviations of the distribution about the elastic kinematic range-angle curve calculated from the multiple scattering in the emulsion and the uncertainty in angle measurement. A total of 2350 tracks have been tabulated in the angular interval 54°<~γ<~78° giving a statistical error matching the systematic errors in plate geometry, beam integration, and track measurement. The results are compared with the Mott cross section integrated over the interval. The theoretical cross section was corrected for (a) proton recoil, (b) the proton magnetic moment, (c) the finite size of the proton's charge and magnetic moment, (d) the radiative correction, including the effect on the cross section of emission of real photons contributing to the observed recoil protons. The result is σexpσtheor=0.988±0.021 (probableerror), using a proton radius of 7.7×10−14 cm, and including a 2.74% radiative correction; the result is not sensitive to the choice of proton radius.
The radiative corrections were not applied in the calculation of the cross sections from the experimental data. Thus the cross sections given in the table are experiment-dependent because the radiative correction depends on the resolution of an experiment. The errors given in the table include systematic and statistical errors combined quadratically. The statistical error varies from 3.5% at 77 DEG to 23.6% at 55 DEG.
These cross sections were recalculated by ZOV from the experimental ones using a radiative correction (see fig.15). Thus they may be considered as an experiment-independent cross sections of a 'pure' process E- P --> E- P.
Electron-proton elastic-scattering cross sections have been measured at the Stanford Linear Accelerator Center for four-momentum transfers squared q 2 from 1.0 to 25.0 (GeVc)2. The electric (GEp) and magnetic (GMp) form factors of the proton were not separated, since angular distributions were not measured at each q 2. However, values for GMp were derived assuming various relations between GEp and GMp. Several theoretical models for the behavior of the proton magnetic form factor at high values of q 2 are compared with the data.
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