Search for narrow nucleon resonances below pion threshold in the H(e,e′π+)X and 2H(e,e′p)X reactions

In two series of high-resolution coincidence experiments at the three-spectrometer facility at MAMI, the H(e, epi+)X and 2H(e, ep)X reactions were studied to search for narrow nucleon resonances below pion threshold. The missing-mass resolution was 0.6-1.6 MeV/c2 full width at half maximum in the proton experiment and 0.9-1.3 MeV/c2 in the deuteron experiment. The experiments covered the missing-mass region from the neutron mass up to about 1050 and 1100 MeV/c2, respectively. None of our measurements showed a signal for narrow resonances to a level of down to 10-4 with respect to the neutron peak in the missing-mass spectra

Measurement of the Electric Form Factor of the Neutron at Q^2 = 0.3-0.8 (GeV/c)^2

The electric form factor of the neutron, G_En, has been measured at the Mainz Microtron by recoil polarimetry in the quasielastic D(e_pol,e'n_pol)p reaction. Three data points have been extracted at squared four-momentum transfers Q^2 = 0.3, 0.6 and 0.8 (GeV/c)^2. Corrections for nuclear binding effects have been applied.Comment: 9 pages, 7 figures, 2 tables. Accepted for publication in EPJ

Beam-helicity asymmetry in photon and pion electroproduction in the Delta(1232) resonance region at Q^2= 0.35 (GeV/c)^2

The beam-helicity asymmetry has been measured simultaneously for the reactions (e p \to e p \gamma) and (e p \to e p \pi^0) in the $\Delta (1232)$ resonance region at $Q^2=$ 0.35 (GeV/c)$^2$. The experiment was performed at MAMI with a longitudinally polarized beam and an out-of-plane detection of the proton. The results are compared with calculations based on Dispersion Relations for virtual Compton scattering and with the MAID model for pion electroproduction. There is an overall good agreement between experiment and theoretical calculations. The remaining discrepancies may be ascribed to an imperfect parametrization of some $\gamma^{(*)} N \to \pi N$ multipoles, mainly contributing to the non-resonant background. The beam-helicity asymmetry in both channels ($\gamma$ and $\pi^0$) shows a good sensitivity to these multipoles and should allow future improvement in their parametrization.Comment: 7 pages, 8 figures, version to appear in EPJ

Investigation of the Exclusive ^{3}He(e,e'pn)p Reaction

Cross sections for the ^{3}He(e,e'pn)p 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 much smaller at higher recoil momentum.Comment: 5, pages, 3 figure