0000000000170419
AUTHOR
S. Schardt
Real and Virtual Compton Scattering (experiments)
This paper deals with Real and Virtual Compton Scattering off the proton at threshold and the way to deduce information about the nucleon polarizabilities.
No evidence for medium effects in the12C(e, e'p)11Bg.s. reaction
The12C(e, e'p)11B g.s reaction has been measured in parallel and anti-parallel kinematics over ap m range of −120<p m<120 MeV/c at a centralT p of 90 MeV. In contrast to previous measurements at NIKHEF, both kinematics can be described without enhancement of the transverse form factor of the bound proton (η=0.98(5)). The spectroscopic factor for this transition as determined with the new Mainz data (S α =1.54(5)) is 22% smaller than the NIKHEF value.
The first Virtual Compton Scattering experiment at MAMI
Abstract Virtual Compton scattering, i.e. the exclusive reaction γ ∗ p → γ′p′ with γ ∗ denoting a virtual photon, provides new insights on the internal structure of the proton. Below π 0 production threshold, this experiment measures the generalized polarizabilities of the proton as defined by Guichon et al [1], [2] and Drechsel et al [3]. These new electromagnetic observables, functions of Q 2 , enlarge the concept of electric (α0 and magnetic (β) polarizabilities in Real Compton Scattering ( Q 2 =0) [4]. The first VCS experiment [5] of this kind was measured at the three spectrometer facility at the Mainz Microtron MAMI for Q 2 =0.33 GeV 2 and we present in this paper the preliminary resu…
Precise pion electroproduction in thep(e, e? ?+)n reaction at W=1125 MeV
The reactione+p →> e+π ++n at c.m. energyW=1125MeV and momentum transfer Q2=0.117GeV2/c2 has been measured. The transverse and longitudinal structure functions have been separated by varying the polarization of the virtual photon (Rosenbluth plot) with a 3 to 4% error. In addition the longitudinal-transverse interference term has been determined measuring the right-left asymmetry with an accuracy of 3%. The experimental data are compared to model calculations, and the sensitivity of the results to the axial and pion formfactors is discussed.
Precise measurements of the neutron magnetic form factor
Abstract The neutron magnetic form factor Gmn has been determined via a measurement of the ratio of cross sections D(e,e′n) and D(e,e′p). The absolute detection efficiency of the neutron detector was measured with high accuracy using tagged neutrons produced from H(n,p)n elastic scattering by means of a high intensity neutron beam. This approach minimizes the model dependence and improves upon the weakest points of previous experiments. Data in the range q2=0.2–0.8 (GeV/c)2 with uncertainties of
Investigation of short-range nucleon-nucleon correlations using the reaction in close to 4π geometry
Abstract Two-proton correlations were studied in close to 4 π geometry using the reaction 12 C (e,e′pp) . The beam energy was 705 MeV, the energy transfer 225 MeV, and the three-momentum transfer 412 MeV/c. The electrons were observed in a large-acceptance magnetic spectrometer in coincidence with protons observed in a BGO crystal ball. Missing energy and momentum, relative momentum and angular distributions were derived and compared with a factorized two-nucleon emission model. Soft-core correlation functions are favoured by the data.
The three-spectrometer facility at the Mainz microtron MAMI
Abstract A set-up of three high-resolution magnetic spectrometers, for simplicity named A, B and C, has been built as the central facility for the precise determination of double and triple coincidence cross sections of hadron knock-out and meson production through the scattering of electrons at the Mainz microtron MAMI. The spectrometers A and C with point-to-point optics in the dispersive plane and parallel-to-point optics in the non-dispersive plane have a solid angle of 28 msr and a momentum acceptance of 20 and 25%, respectively. They each consist of a quadrupole, a sextupole and two dipole magnets, reaching maximum momenta of 735 and 550 MeV/c, respectively. The spectrometer B has a s…
Virtual Compton Scattering at MAMI γ*p→ γ1p1
The virtual Compton scattering (VCS) is the electron scattering on a proton which radiates a real photon before being detected. The new observables, called Generalized Polarizabilities (GP), extracted from this VCS at threshold can be understood as the deformation of the charge and current distributions of the proton [1]. These GP are functions of the mass of the virtual photon Q2. In real Compton scattering (Q2 = 0), some polarizabilities of the nucleon are already measured [2]. With the VCS, we will generalize these observables by measuring them at different values of Q2.
Model-independent separation of structure functions over an extended kinematical region
A method for the separation of structure functions in (e, e′ p) experiments is proposed, which is an extension of the traditional Rosenbluth-type techniques of [1,2]. In our approach, we use a very flexible Ansatz to describe the structure functions within an extended kinematical regionG and determine its free parameters with a x2 minimization. The procedure is tested by pseudo data (12C(e, e′p)11Bg.s.) in the quasi-free region.
Pion electroproduction in the 3He(e,é π+)3H reaction at intermediate energies
Abstract The differential coincident pion electroproduction cross section in the 3 He(e,e π + ) 3 H reaction has been measured with high resolution with the three-spectrometer set-up at the Mainz Microtron (MAMI) electron accelerator. Measurements were performed at the four incident energies E 0 = 855, 675, 600, and 555 MeV at fixed four-momentum transfer Q 2 = 0.045 GeV 2 , with the pions detected in parallel kinematics. This enables a separation of the measured cross section into the transverse and longitudinal structure functions by means of the Rosenbluth method. The experimental data are compared to model calculations, in which the elementary pion production amplitude includes the stan…
Large recoil momenta in the D(e,e′p)n reaction
Abstract The D(e,e′p)n reaction cross section has been measured for recoil momenta ranging from 17 MeV/c up to 950 MeV/c at momentum transfers between 600 MeV/c and 700 MeV/c. At recoil momenta above 400 MeV/c, the gross features of the cross section are only reproduced if virtual nucleon excitations are included in the calculations.
The first dedicated Virtual Compton Scattering experiment at MAMI
We measured the absolute cross sections for photon electro-production off the proton, ep to ep gamma , with the high resolution spectrometers at MAMI at momentum transfer q=600 MeV/c and photon polarization epsilon =0.62. We covered the momentum range for the outgoing real photon q'=33/111 MeV/c. From the extracted virtual Compton scattering amplitude we deduce values for two structure functions related to the generalized polarizabilities of the proton.
Virtual compton scattering under π0 threshold at Q2=0.33 GeV2. Preliminary results
We have measured the absolute unpolarized cross sections for photon electro-production off the proton ep → epγ with the Three-Spectrometer-Setup at MAMI at a momentum transfer q=600 MeV/c and a virtual photon polarization ɛ=0.62. The momentum q ′ of the outgoing real photon range from 33 to 111 MeV/c. We extracted two combinations of the recently introduced generalized polarizabilities [1,2].
High-momentum components in the 1p orbitals of 16O
Abstract We have investigated that part of the proton momentum distribution of 16O that is linked through the (e, e′p) reaction to low-lying discrete states in 15N. The MAMI facility with its new generation of 100%-duty-cycle electron accelerator has allowed to cover in this experiment the previously not accessible momentum range of 265
Forward-AngleH3e(e,e′π±)Coincident Electroproduction and the Search forΔ's in the Ground State ofH3e
Forward-angle coincident electroproduction cross sections of charged pions from ${}^{3}\mathrm{He}$ have been measured at electron energies ${E}_{0}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}855$, 675, 600, and 555 MeV. The overall features of the data for energy transfers of $\ensuremath{\omega}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}370$ to 430 MeV with pions detected along the momentum transfer axis are reproduced in terms of a microscopic model, including pole terms, final state rescattering and produced and preformed $\ensuremath{\Delta}$ resonances. Separation of the cross section into its longitudinal and transverse parts was performed at ${Q}^{2}\phantom{\rule{0ex…
"Table 6" of "Precise pion electroproduction in the p (e, e-prime pi+) n reaction at W = 1125-MeV"
Angle PHI(P=4) is the angle between the scattering plane (defined by 1 and 3 particles) and the reaction plane (defined by 4 and 5 particles).
"Table 4" of "Precise pion electroproduction in the p (e, e-prime pi+) n reaction at W = 1125-MeV"
Angle PHI(P=4) is the angle between the scattering plane (defined by 1 and 3 particles) and the reaction plane (defined by 4 and 5 particles).
"Table 2" of "Precise pion electroproduction in the p (e, e-prime pi+) n reaction at W = 1125-MeV"
Angle PHI(P=4) is the angle between the scattering plane (defined by 1 and 3 particles) and the reaction plane (defined by 4 and 5 particles).
"Table 1" of "Virtual Compton scattering under pi0 threshold at Q**2 = 0.33-GeV**2: Preliminary results."
No description provided.
"Table 5" of "Precise pion electroproduction in the p (e, e-prime pi+) n reaction at W = 1125-MeV"
Angle PHI(P=4) is the angle between the scattering plane (defined by 1 and 3 particles) and the reaction plane (defined by 4 and 5 particles).
"Table 3" of "Precise pion electroproduction in the p (e, e-prime pi+) n reaction at W = 1125-MeV"
Angle PHI(P=4) is the angle between the scattering plane (defined by 1 and 3 particles) and the reaction plane (defined by 4 and 5 particles).
"Table 1" of "Precise pion electroproduction in the p (e, e-prime pi+) n reaction at W = 1125-MeV"
Angle PHI(P=4) is the angle between the scattering plane (defined by 1 and 3 particles) and the reaction plane (defined by 4 and 5 particles).