The radiative corrections to elastic electron-proton scattering are analyzed in a hadronic model including the finite size of the nucleon. For initial electron energies above 8 GeV and large scattering angles, the proton vertex correction in this model increases by at least 2% of the overall factor by which the one-photon exchange cross section must be multiplied. In addition, we refine the mathematical treatment, removing many of the approximations made in the generally used expressions previously obtained by Mo and Tsai. In particular, the contribution of soft photon emission is calculated exactly. Results are presented for some kinematics at high momentum transfer and compared with the expressions of Mo and Tsai.

Measurement of two-and three-nucleon shortrange correlation probabilities in nuclei KS The ratios of inclusive electron scattering cross sections of 4 He, 12 C, and 56 Fe to 3 He have been measured at 1 < x B < 3. At Q 2 > 1:4 GeV 2 , the ratios exhibit two separate plateaus, at 1:5 < x B < 2 and at x B > 2:25. This pattern is predicted by models that include 2-and 3-nucleon short-range correlations (SRC). Relative to A 3, the per-nucleon probabilities of 3-nucleon SRC are 2.3, 3.1, and 4.4 times larger for A 4, 12, and 56. This is the first measurement of 3-nucleon SRC probabilities in nuclei.

The ratios of inclusive electron scattering cross sections of 4 He, 12 C, and 56 Fe to 3 He have been measured for the first time. It is shown that these ratios are independent of x B at Q 2 Ͼ1.4 GeV 2 for x B Ͼ1.5, where the inclusive cross section depends primarily on the high momentum components of the nuclear wave function. The observed scaling shows that the momentum distributions at high-momenta have the same shape for all nuclei and differ only by a scale factor. The observed onset of the scaling at Q 2 Ͼ1.4 GeV 2 and x B Ͼ1.5 is consistent with the kinematical expectation that two-nucleon short range correlations ͑SRC͒ dominate the nuclear wave function at p m տ300 MeV/c. The values of these ratios in the scaling region can be related to the relative probabilities of SRC in nuclei with Aу3. Our data, combined with calculations and other measurements of the 3 He/deuterium ratio, demonstrate that for nuclei with Aу12 these probabilities are 4.9-5.9 times larger than in deuterium, while for 4 He it is larger by a factor of about 3.8.

Differential cross sections for the reaction γ p → p π 0 have been measured with the CEBAF Large Acceptance Spectrometer (CLAS) and a tagged photon beam with energies from 0.675 to 2.875 GeV. The results reported here possess greater accuracy in the absolute normalization than previous measurements. They disagree with recent CB-ELSA measurements for the process at forward scattering angles. Agreement with the SAID and MAID fits is found below 1 GeV. The present set of cross sections has been incorporated into the SAID database, and exploratory fits have been extended to 3 GeV. Resonance couplings have been extracted and compared to previous determinations.

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