0000000001306975
AUTHOR
P. Bartsch
showing 18 related works from this author
Real and Virtual Compton Scattering (experiments)
1999
This paper deals with Real and Virtual Compton Scattering off the proton at threshold and the way to deduce information about the nucleon polarizabilities.
The first Virtual Compton Scattering experiment at MAMI
1999
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…
Measurement of the ExclusiveH3e(e,e′p)Reaction Below the Quasielastic Peak
2004
New, high-precision measurements of the 3He(e,ep) reaction using the A1 Collaboration spectrometers at the Mainz microtron MAMI are presented. These were performed in antiparallel kinematics at energy transfers below the quasielastic peak, and at a central momentum transfer of 685 MeV/c. Cross sections and distorted momentum distributions were extracted and compared to theoretical predictions and existing data. The longitudinal and transverse behavior of the cross section was also studied. Sizable differences in the cross-section behavior from theoretical predictions based on the plane wave impulse approximation were observed in both the two- and three-body breakup channels. Full Faddeev-ty…
Measurement of the Recoil Polarization in thep(e→,e′p→)π0Reaction at theΔ(1232)Resonance
2001
The recoil proton polarization has been measured in the $p(\stackrel{\ensuremath{\rightarrow}}{e}{,e}^{\ensuremath{'}}\stackrel{\ensuremath{\rightarrow}}{p}){\ensuremath{\pi}}^{0}$ reaction in parallel kinematics around $W\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1232\phantom{\rule{0ex}{0ex}}\mathrm{MeV}$, ${Q}^{2}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.121\phantom{\rule{0ex}{0ex}}(\mathrm{GeV}/c{)}^{2}$, and $\ensuremath{\epsilon}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.718$ using the polarized cw electron beam of the Mainz Microtron. All three proton polarization components, ${P}_{x}/{P}_{e}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}(\ensuremath{-…
Virtual Compton Scattering and polarizabilities
1999
Abstract Virtual Compton Scattering (VCS) off the proton below pion threshold allows access to generalized polarizabilities of the proton. These observables measure the response of the nucleon to low energy electromagnetic field perturbations. This paper presents a comparison with Real Compton Scattering and also results for the first dedicated VCS experiment performed at the Mainz Microtron MAMI with high resolution spectrometers at Q2 = 0.33 GeV2.
The horizontal drift chambers for the focal plane proton-polarimeter of the 3-spectrometer setup at MAMI
2002
Abstract Large-area horizontal drift chambers have been built for use in a proton polarimeter. A gas mixture of 20% argon and 80% ethane is used. The left–right assignment is achieved by measuring the difference of the signals induced on neighboring potential wires. A spatial resolution of 300 μm is achieved.
Measurement of GEp/GMp via polarization transfer at Q2 = 0.4 GeV /c2
2001
The polarization transfer from longitudinally polarized electrons to protons in the elastic scattering p( e, e' p) has been measured around Q2 = 0.4 (GeV/c)2 with the three-spectrometer facility at the Mainz microtron MAMI. From this polarization transfer the ratio G Ep/(G Mp/μp) has been determined. The ratio is found to be slightly less than unity in agreement with recent results from other laboratories and from the Rosenbluth separation of cross-sections measured with unpolarized electrons.
Virtual Compton Scattering at MAMI γ*p→ γ1p1
1999
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.
Polarization transfer in the 4HeH reaction
2001
Abstract Polarization transfer in the 4He ( e → ,e′ p → ) 3 H reaction at a Q2 of 0.4 (GeV/c)2 was measured at the Mainz Microtron MAMI. The ratio of the transverse to the longitudinal polarization components of the ejected protons was compared with the same ratio for elastic ep scattering. The results are consistent with a recent fully relativistic calculation which includes a predicted medium modification of the proton form factor based on a quark–meson coupling model.
Final State Interaction Effects in 3He(e ,e'p)
2003
Abstract Asymmetries in quasi-elastic 3 He ( e → , e ′ p ) have been measured at a momentum transfer of 0.67 (GeV/ c ) 2 and are compared to a calculation which takes into account relativistic kinematics in the final state and a relativistic one-body current operator. With an exact solution of the Faddeev equation for the 3 He -ground state and an approximate treatment of final state interactions in the continuum good agreement is found with the experimental data.
The first dedicated Virtual Compton Scattering experiment at MAMI
1999
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.
Neutral Pion Threshold Production atQ2=0.05GeV2/c2and Chiral Perturbation Theory
2001
New data are presented on the $p({e,e}^{\ensuremath{'}}p){\ensuremath{\pi}}^{0}$ reaction at threshold at a four-momentum transfer of ${Q}^{2}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.05{\mathrm{GeV}}^{2}{/c}^{2}$. The data were taken with the three-spectrometer setup of the A1 Collaboration at the Mainz Microtron MAMI. The complete center of mass solid angle was covered up to a center of mass energy of 4 MeV above threshold. Combined with measurements at three different values of the virtual photon polarization $\ensuremath{\epsilon}$, the structure functions ${\ensuremath{\sigma}}_{T}$, ${\ensuremath{\sigma}}_{L}$, ${\ensuremath{\sigma}}_{\mathrm{TT}}$, and ${\ensuremath{\sigma…
Virtual compton scattering under π0 threshold at Q2=0.33 GeV2. Preliminary results
1999
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].
Measurement of the Beam-Helicity Asymmetry in thep(e→,e′p)π0Reaction at the Energy of theΔ(1232)Resonance
2002
In a p((e) over right arrow, e' p)pi(0) out-of-plane coincidence experiment at the three-spectrometer setup of the Mainz Microtron MAMI, the beam-helicity asymmetry has been precisely measured around the energy of the Delta(1232) resonance and Q(2) = 0.2(GeV/c)(2). The results are in disagreement with three up-to-date model calculations. This is interpreted as a lack of understanding of the nonresonant background, which in dynamical models is related to the pion cloud.
Evidence for narrow Δ0(1232) states in the 12 C(e,e'pπ−}11 C Reaction
1999
The reaction 12C(e,e'Δ0)11C →12C(e,e'pπ−)11C was investigated at the Mainz Microtron MAMI in a triple coincidence measurement using the three spectrometer setup of the A1 Collaboration. The good missing mass resolution of σm= 0.27 MeV/c2 allowed to select the events belonging to the ground state of 11C. Cutting on these events the excitation energy spectra of 12CΔ0 show evidence for two peaks of about 4 MeV width (FWHM) at 282 MeV and 296 MeV with a significance of about 4.5 standard deviations. The peaks are interpreted in a simple weak coupling model as bound Δ0 states in 12CΔ0.
"Table 1" of "Virtual Compton scattering under pi0 threshold at Q**2 = 0.33-GeV**2: Preliminary results."
1999
No description provided.
"Table 2" of "Polarization transfer in the He-4(e(pol.),e' p(pol.)H-3 reaction."
2004
No description provided.
"Table 1" of "Polarization transfer in the He-4(e(pol.),e' p(pol.)H-3 reaction."
2004
No description provided.