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We have measured (y, p) and (y, n) differential yields at 90' for the two-body photodisintegration of He using tagged photons of energy E"=25-60 MeV. Data for both channels were obtained simultaneously using windowless hE-E telescopes to detect the He and H recoils. The ratio of our angleintegrated yields, which is insensitive to systematic uncertainties due to the simultaneity of the measurements, agrees with calculations employing only charge-symmetric nuclear interactions. Thus, within the present errors, our data show no evidence of a significant charge-symmetry violation in He in this energy range. PACS numbers: 25.20.Dc, 25. 10.+s, 27. ]0.+h The question of charge symmetry in He has been a long-standing problem in nuclear physics. If charge symmetry is strictly valid, then the ratio of the two-body photodisintegration cross sections, R"=a(y-,p)/o(y, n), is expected to be unity (for pure E I radiation). EA'ects such as Coulomb interactions or non-E 1 multipoles can slightly modify this value, increasing the ratio to R~-1.1 in the photon energy range E"=25-35 MeV. The problem was summarized in 1983 by Calarco, Berman, and Donnelly [I] in a comprehensive review of all photonuclear (and capture) data up to that time, leading to the surprising conclusion that R"=1. 7-1.2 for E, =25-35 MeV, dilfering substantially from the simple charge-symmetry prediction. Theoretical attempts which include charge-symmetric nuclear interactions in a shell model [2,3] and a resonating group model [4,5] have failed to reproduce this large value of the ratio. It should be noted, however, that the recommended cross sections comprising the ratio in Ref. [I] were determined from in ditidual measurements of the (y,p) and (y, n) channels separately. Since this review, three new measurements of the proton channel have been reported [6-8]. The data from [6,7] are more consistent with the recommended photoneutron cross section, while [8] reports a cross section nearly twice as large, in agreement with the recommended proton cross section. The only new published neutron data are from a capture reaction [9] which finds a peak cross-section value that is consistent with the recommended neutron value.In addition to these new measurements of the individual two-body channels, a recent elastic photon scattering experiment [10] inferred the total photoabsorption cross section in a model-independent manner through the optical theorem and a dispersion relation. While their result can say nothing about the relative contributions of the (y,p) and (y, n) channels (and hence, the ratio), it does impose a significant constraint on the sum of the two cross sections. This new photon scattering result (a) agrees with the sum of the recommended cross sections in Ref. [I] (which give the large value of R"), (b) disagrees with the sum of the recent photoproton data [6,7] and the recommended photoneutron values (where R" is closer to unity), (c) agrees with the sum of Ref. [8] and the recommended neutron cross section, and (d) agrees with the sum of the latest...

We present a direct calculation of the cross section for the reaction 3 He(e, e ′ p) including the radiation tail originating from bremsstrahlung processes. This calculation is compared to measured cross sections. The calculation is carried out from within a Monte Carlo simulation program so that acceptance-averaging effects, along with a subset of possible energy losses, are taken into account. Excellent agreement is obtained between our calculation and measured data, after a correction factor for higherorder bremsstrahlung is devised and applied to the tail. Industry-standard radiative corrections fail miserably for these data, and we use the results of our calculation to dissect the failure. Implications for design and analysis of experiments in the Jefferson-Lab energy domain are discussed. 13.40.Ks,24.10.Lx,25.30.Fj

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Precision studies of the reaction 3 He͑e, e 0 p͒ using the three-spectrometer facility at the Mainz microtron MAMI are presented. All data are for quasielastic kinematics at j qj 685 MeV͞c. Absolute cross sections were measured at three electron kinematics. For the measured missing momenta range from 10 to 165 MeV͞c, no strength is observed for missing energies higher than 20 MeV. Distorted momentum distributions were extracted for the two-body breakup and the continuum. The longitudinal and transverse nature of the cross sections is well described by a widely used prescription of the offshell electron-nucleon cross section. The results are compared to modern three-body calculations and to previous data.PACS numbers: 21.45. + v, 25.10. + s, 25.30.Dh, 25.30.Fj The study of few-body nuclear systems has acquired new importance due to recent developments on both theoretical and experimental fronts. Several schemes have been developed to perform microscopic calculations which are based on the NN interaction rather than on a mean-field approach. These include nonrelativistic Faddeev-type calculations for three-body systems [1,2] and Monte Carlo variational calculations for three-and four-body systems [3]. Fully relativistic calculations are also being developed for three bodies [4]. New experimental facilities with high-quality continuous-wave (cw) electron beams and high-resolution spectrometers provide the means to rigorously test these modern calculations. In particular, precision measurements of electromagnetic response functions, which are selectively sensitive to the various components of the nuclear currents, are possible.The first results of a program to study 3,4 He͑e, e 0 p͒ at a fixed three-momentum transfer, q j qj 685 MeV͞c, and three energy transfers, v, corresponding to kinematics on top of the quasielastic peak, well above it ("dip") and well below it are reported here. By varying the energy transfer, we hope to selectively enhance or suppress various effects contributing to the interaction. In order to further understand these contributing effects, we studied the longitudinal and transverse components of the cross section by measuring it at three electron scattering angles (virtual photon polarizations, e). The ongoing research program was carried out in the three-spectrometer facility [5] at the Mainz microtron MAMI by the A1 Collaboration. The results reported here are from measurements performed on 3 He in quasielastic kinematics (x B 1; v 228 MeV), where the dominant mechanism is expected to be the quasifree knockout of a single proton. Further experimental details are described in Ref. [6].Few exclusive and semiexclusive electron-scattering measurements have been performed on 3 He, and the existing data are inconclusive. The 3 He͑e, e 0 p͒ reaction was measured at Saclay [7] at three-momentum transfers of 300 and 430 MeV͞c. Measurements covered the missing energy range 0-70 MeV and missing momentum range 0 # p m # 300 MeV͞c. Momentum distributions were extracted for the two-body breakup channel...