Measurements of the forward-angle differential cross section for elastic electron-proton scattering were made in the range of momentum transfer from Q2 = 2.9 to 31.3 (GeV/c)2 using an electron beam at the Stanford Linear Accelerator Center. The data span six orders of magnitude in cross section. Combined statistical and systematic uncertainties in the cross section measurements ranged from 3.6% at low Q2 to 19% at high Q2. These data have been used to extract the proton magnetic form factor Gb(Q2) and Dirac form-factor F:(Q2) by using form factor scaling. The logarithmic falloff of Q4F'f expected from leading twist predictions of perturbative quantum chromodynamics (&CD) is consistent with the new data at high Q 2. Some nonperturbative and hybrid calculations also agree with our result 9.

We report on the results of the 3 He( 3 He,2p) 4 He experiment at the underground accelerator facility LUNA (Gran Sasso). For the first time the lowest projectile energies utilized for the cross section measurement correspond to energies below the center of the solar Gamow peak (E 0 =22 keV). The data provide no evidence for the existence of a hypothetical resonance in the energy range investigated. Although no extrapolation is needed anymore (except for energies at the low-energy tail of the Gamow peak), the data must be corrected for the effects of electron screening, clearly observed the first time for the 3 He( 3 He,2p) 4 He reaction. The effects are however larger than expected and not understood, leading presently to the largest uncertainty on the quoted S b (E 0 ) value for bare nuclides (=5.40 MeV b).

No abstract

Measurements of the deuteron elastic magnetic structure function B(Q') are reported at squared four-momentum transfer values 1.20~Qi~2.77 (GeV/c)'. Also reported are values for the proton magnetic form factor Gstr(Q2) at 11 Q values between 0.49 and 1.75 (GeV/c) . The data were obtained using an electron beam of 0.5 to 1.3 GeV. Electrons backscattered near 180' were detected in coincidence with deuterons or protons recoiling near 0 in a large solid-angle double-arm spectrometer system. The data for B(Q ) are found to decrease rapidly from Q =1.2 to 2 (GeV/c), and then rise to a secondary maximum around Q'=2. 5 (GeV/c)'. Reasonable agreement is found with several different models, including those in the relativistic impulse approximation, nonrelativistic calculations that include meson-exchange currents, isobar configurations, and six-quark configurations, and one calculation based on the Skyrme model. All calculations are very sensitive to the choice of deuteron wave function and nucleon form factor parametrization. The data for GMr(Q') are in good agreement with the empirical dipole fit.

No abstract