[en] A comprehensive set of ⁴He(γ,n) absolute cross-section measurements was performed at MAX-lab in Lund, Sweden. Tagged photons from 23< E_γ<70 MeV were directed toward a liquid ⁴He target, and neutrons were identified using pulse-shape discrimination and the time-of-flight technique in two liquid-scintillator detector arrays. Seven-point angular distributions have been measured for 14 photon energies. The results have been subjected to complementary transition-coefficient and Legendre-coefficient analyses. The results are also compared to experimental data measured at comparable photon energies as well as recoil-corrected continuum shell-model, resonating group method, and effective interaction hyperspherical-harmonic expansion calculations. For photon energies below 29 MeV, the angle-integrated data are significantly larger than the values recommended by Calarco, Berman, and Donnelly in 1983

[en] Cross sections for the ³He(e,e^'pn)¹H reaction were measured for the first time at energy transfers of 220 and 270 MeV for several momentum transfers ranging from 300 to 450 MeV/c. Cross sections are presented as a function of the momentum of the recoil proton and the momentum transfer. Continuum Faddeev calculations using the Argonne V18 and Bonn-B nucleon-nucleon potentials overestimate the measured cross sections by a factor 5 at low recoil proton momentum with the discrepancy becoming smaller at higher recoil proton momentum.

[en] A new upper limit of 2.3x10^-4 on the branching ratio of the decay ω→ηπ⁰ has been obtained using the Crystal Ball multiphoton spectrometer at the Mainz Microtron MAMI. This decay is forbidden by charge-conjugation invariance of the strong and electromagnetic interactions. We have also obtained the upper limit of 2.3x10^-4 for the forbidden decay ω→3π⁰ and the upper limit of 2.4x10^-4 for ω→2π⁰.

[en] The helicity dependence of the γp→nπ⁺ reaction has been measured for the first time in the photon energy range from 450 to 790 MeV. The experiment, performed at the Mainz Microtron (MAMI), used a 4π-detector system, a circularly polarized, tagged photon beam, and a longitudinally polarized frozen-spin target. Although these polarized data are mainly sensitive to mechanisms involving the D₁₃(1520) resonance, a cusp structure at the η production threshold can be clearly observed. These data are significantly different from the predictions of the existing multipole analyses and are used to determine the helicity amplitudes of the D₁₃(1520) and S₁₁(1535) resonances with improved accuracy

[en] The γp→ηp reaction has been measured with the Crystal Ball and TAPS multiphoton spectrometers in the energy range from the production threshold of 707 MeV to 1.4 GeV (1.49≤W≤1.87 GeV). Bremsstrahlung photons produced by the 1.5-GeV electron beam of the Mainz Microtron MAMI-C and momentum analyzed by the Glasgow tagging spectrometer were used for the η-meson production. Our accumulation of 3.8x10⁶ γp→ηp→3π⁰p→6γp events allows a detailed study of the reaction dynamics. The γp→ηp differential cross sections were determined for 120 energy bins and the full range of the production angles. Our data show a dip near W=1680 MeV in the total cross section caused by a substantial dip in η production at forward angles. The data are compared to predictions of previous SAID and MAID partial-wave analyses and to the latest SAID and MAID fits that included our data.

[en] A measurement of the helicity dependence of the total inclusive photoabsorption cross section on the deuteron was carried out at MAMI (Mainz) in the energy range 200< E_γ<800 MeV. The experiment used a 4π detection system, a circularly polarized tagged photon beam and a frozen-spin target which provided longitudinally polarized deuterons. The contribution to the Gerasimov-Drell-Hearn sum rule for the deuteron determined from the data is 407±20(stat)±24(syst) μb for 200< E_γ<800 MeV

[en] The photon asymmetry Σ of the D(γ^→,p)n reaction has been measured across the photon energy range 160 - 410 MeV at the Mainz Microtron MAMI. Linearly polarized photons were obtained from coherent bremsstrahlung and their energies were determined with the Glasgow tagging spectrometer. The large acceptance detector DAPHNE enabled the outgoing protons to be measured over the complete azimuthal range and for polar angles from 35 degree to 155 degree in the c.m. system. The data are compared with existing results and recent theoretical calculations. (author)