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356
result(s) for
"Hehl, T"
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3He(e,e′pp) and 3He(e,e′pn) reactions at AmPS and MAMI
This paper reports on measurements of the
3
He(
e
,
e
′
pp
) reaction measured at AmPS and the
3
He(
e
,
e
′
pn
) reaction measured at MAMI. The measurements were performed in similar kinematics to allow a comparison to be made between the cross sections of the two reactions. Results are shown for both reactions together with a comparison for the
3
He(
e
,
e
′
pp
) data with continuum Faddeev calculations.
Journal Article
Structure of the Nucleon Investigated by Compton Scattering
Experimental differential cross sections for Compton scattering by the proton measured with the LARge Acceptance arrangement at the tagged-photon facility MAMI (Mainz) are interpreted in terms of the nonsubtracted dispersion theory based on the SAID-SM99K parameterization of photo-meson amplitudes. Using the new global average for the difference of electric and magnetic polarizabilities of the proton α - β = (10.5 ± 0.9stat+syst ± 0.7model) × 10-4fm3 a backward spin-polarizability of γπ = (-37.1 ± 0.6stat+syst ± 3.5model) × 10-4fm4 and a E2/M1 ratio of EMR(340 MeV)=(-1.7 ± 0.4stat+syst ± 0.2model) % have been obtained.
Book Chapter
Measurement of the neutron electric to magnetic form factor ratio at Q2 = 1.58 GeV2 using the reaction 3He(e,e'n)pp
A measurement of beam helicity asymmetries in the reaction 3He(e,e'n)pp has been performed at the Mainz Microtron in quasielastic kinematics in order to determine the electric to magnetic form factor ratio of the neutron, GEn/GMn, at a four momentum transfer Q2 = 1.58 GeV2. Longitudinally polarized electrons were scattered on a highly polarized 3He gas target. The scattered electrons were detected with a high-resolution magnetic spectrometer, and the ejected neutrons with a dedicated neutron detector composed of scintillator bars. To reduce systematic errors data were taken for four different target polarization orientations allowing the determination of GEn/GMn from a double ratio. We find mu_n GEn/GMn = 0.250 +/- 0.058(stat.) +/- 0.017 (sys.).
Paper
Knockout of proton-neutron pairs from \\(^{16}\\)O with electromagnetic probes
After recent improvements to the Pavia model of two-nucleon knockout from \\(^{16}\\)O with electromagnetic probes the calculated cross sections are compared to experimental data from such reactions. Comparison with data from a measurement of the \\(^{16}\\)O(e,e\\('\\)pn) reaction show much better agreement between experiment and theory than was previously observed. In a comparison with recent data from a measurement of the \\(^{16}\\)O(\\(\\gamma\\),pn) reaction the model over-predicts the measured cross section at low missing momentum.
Paper
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.
Paper
Three-nucleon mechanisms in photoreactions
The \\(^{12}\\)C\\((\\gamma,ppn)\\) reaction has been measured for E\\(_{\\gamma}\\)=150-800 MeV in the first study of this reaction in a target heavier than \\(^3\\)He. The experimental data are compared to a microscopic many body calculation. The model, which predicts that the largest contribution to the reaction arises from final state interactions following an initial pion production process, overestimates the measured cross sections and there are strong indications that the overestimate arises in this two-step process. The selection of suitable kinematic conditions strongly suppresses this two-step contribution leaving cross sections in which up to half the yield is predicted to arise from the absorption of the photon on three interacting nucleons and which agree with the model. The results indicate \\((\\gamma,3N)\\) measurements on nuclei may be a valuable tool for obtaining information on the nuclear three-body interaction.
Paper
First measurements of the ^16O(e,e'pn)^14N reaction
This paper reports on the first measurement of the ^16O(e,e'pn)^14N reaction. Data were measured in kinematics centred on a super-parallel geometry at energy and momentum transfers of 215 MeV and 316 MeV/c. The experimental resolution was sufficient to distinguish groups of states in the residual nucleus but not good enough to separate individual states. The data show a strong dependence on missing momentum and this dependence appears to be different for two groups of states in the residual nucleus. Theoretical calculations of the reaction using the Pavia code do not reproduce the shape or the magnitude of the data.
Paper
Measurement of the pi^+ meson polarizabilities via the gamma p->gamma pi^+ n reaction
An experiment on the radiative pi^+ meson photoproduction from the proton (gamma p->gamma pi^+ n) was carried out at the Mainz Microtron MAMI in the kinematic region 537 MeV
Paper
Compton Scattering by the Proton using a Large-Acceptance Arrangement
Compton scattering by the proton has been measured using the tagged-photon facility at MAMI (Mainz) and the large-acceptance arrangement LARA. The new data are interpreted in terms of dispersion theory based on the SAID-SM99K parameterization of photo-meson amplitudes. It is found that two-pion exchange in the t-channel is needed for a description of the data in the second resonance region. The data are well represented if this channel is modeled by a single pole with mass parameter m(sigma)=600 MeV. The asymptotic part of the spin dependent amplitude is found to be well represented by pi-0-exchange in the t-channel. A backward spin-polarizability of gamma(pi)=(-37.1+-0.6(stat+syst)+-3.0(model))x10^{-4}fm^4 has been determined from data of the first resonance region below 455 MeV. This value is in a good agreement with predictions of dispersion relations and chiral pertubation theory. From a subset of data between 280 and 360 MeV the resonance pion-photoproduction amplitudes were evaluated leading to a E2/M1 multipole ratio of the p-to-Delta radiative transition of EMR(340 MeV)=(-1.7+-0.4(stat+syst)+-0.2(model))%. It was found that this number is dependent on the parameterization of photo-meson amplitudes. With the MAID2K parameterization an E2/M1 multipole ratio of EMR(340 MeV)=(-2.0+-0.4(stat+syst)+-0.2(model))% is obtained.
Paper
Compton Scattering by the Proton
Compton scattering by the proton has been measured over a wide range covering photon energies 250 MeV < E_\\gamma < 800 MeV and photon scattering angles 30^0 < \\theta^{lab}_\\gamma < 150^0, using the tagged-photon facility at MAMI (Mainz) and the large-acceptance arrangement LARA. The data are in good agreement with the dispersion theory based on the SAID-SM99K parameterization of photo-meson amplitudes. From the subset of data between 280 and 360 MeV the resonance pion-photoproduction amplitudes were evaluated leading to the multipole E2/M1 ratio EMR(340 MeV) =(-1.6 \\pm 0.4(stat+syst) \\pm 0.2(model)%. From all data below 455 MeV the proton's backward spin polarizability was determined to be \\gamma_\\pi=(-37.9 \\pm 0.6(stat+syst) \\pm 3.5(model))x10^{-4}fm^4.
Paper