-
The Collaboration,
M. Weis,
P. Bartsch,
D. Baumann,
J. Bermuth,
A. M. Bernstein, K. Bohinc,
R. Böhm,
M. Ding,
M. O. Distler, [......],
R. Neuhausen,
M. M. Pavan,
Th. Pospischil,
M. Potokar,
G. Rosner,
H. Schmieden,
M. Seimetz,
S. Širca,
A. Wagner,
Th. Walcher
[show abstract]
[hide abstract]
ABSTRACT: The differential cross-sections σ0 = σT + εσL , σLT , and σTT of p0 \pi^{0}_{} electroproduction from the proton were measured from threshold up to an additional center-of-mass energy of 40MeV, at a value
of the photon four-momentum transfer of Q
2 = 0.05 GeV2/c2 and a center-of-mass angle of θ = 90° . By an additional out-of-plane measurement with polarized electrons σLT' was determined. This showed for the first time the presence of an imaginary part of the s -wave above the p+ \pi^{+}_{} threshold, which is usually interpreted as a unitary cusp. The predictions of the Heavy Baryon Chiral Perturbation Theory
(HBChPT) are in disagreement with these data. On the other hand, the data are somewhat better predicted by the MAID phenomenological
model and are in good agreement with the dynamical model DMT.
European Physical Journal A 09/2008; 38(1):27-33. · 2.19 Impact Factor
-
M. Weis,
P. Bartsch,
D. Baumann,
J. Bermuth,
A. M. Bernstein, K. Bohinc,
R Böhm,
M Ding,
M. O. Distler,
I. Ewald, [......],
R. Neuhausen,
M. M. Pavan,
Th. Pospischil,
M. Potokar,
G Rosner,
H. Schmieden,
M. Seimetz,
S. Širca,
A Wagner,
Th. Walcher
[show abstract]
[hide abstract]
ABSTRACT: The differential cross sections \sigma_0=\sigma_T+\epsilon \sigma_L, \sigma_{LT}, and \sigma_{TT} of \pi^0 electroproduction from the proton were measured from threshold up to an additional center of mass energy of 40 MeV, at a value of the photon four-momentum transfer of Q^2= 0.05 GeV^2/c^2 and a center of mass angle of \theta=90^\circ. By an additional out-of-plane measurement with polarized electrons \sigma_{LT'} was determined. This showed for the first time the cusp effect above the \pi^+ threshold in the imaginary part of the s-wave. The predictions of Heavy Baryon Chiral Perturbation Theory are in disagreement with these data. On the other hand, the data are somewhat better predicted by the MAID phenomenological model and are in good agreement with the dynamical model DMT.
06/2007;
-
K. A. Aniol,
M. B. Epstein,
E. Gama,
D. J. Margaziotis,
W. Bertozzi,
J. P. Chen,
D. Dale,
R. E. J. Florizone,
S. Gilad,
A. J. Sarty, [......],
Th. Walcher,
M. Kuss,
A. Richter,
G. Schrieder, K. Bohinc,
M. Potokar,
S. Širca,
J. M. Udias,
Javier R. Vignote,
R. Schiavilla
[show abstract]
[hide abstract]
ABSTRACT: We have measured the 4He(e, ep)3H reaction at missing momenta of 130-300 MeV/c using the three-spectrometer facility at the Mainz microtron MAMI. Data were taken in perpendicular kinematics to allow us to determine the response function RLT and the asymmetry term ATL. The data are compared to both relativistic and non-relativistic calculations.
European Physical Journal A 11/2004; 22(3):449-454. · 2.19 Impact Factor
-
A Kozlov,
A J Sarty,
K A Aniol,
P Bartsch,
D Baumann,
W Bertozzi, K Bohinc,
R Böhm,
J P Chen,
D Dale, [......],
J A Templon,
M N Thompson,
A Wagner,
Th Walcher,
M Weis,
J Zhao,
Z-L Zhou,
J Golak,
W Glöckle,
H Witała
[show abstract]
[hide abstract]
ABSTRACT: New, high-precision measurements of the 3He(e,e(')p) 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-type calculations account for some of the observed excess cross-section, but significant differences remain.
Physical Review Letters 10/2004; 93(13):132301. · 7.37 Impact Factor
-
K. A. Aniol,
M.B. Epstein,
E. Gama,
D J Margaziotis,
W. Bertozzi,
J P Chen,
D Dale,
R. E. J. Florizone,
S Gilad,
A. J. Sarty, [......],
Th. Walcher,
M. Kuss,
A Richter,
G. Schrieder, K. Bohinc,
M. Potokar,
S. Sirca,
J. M. Udias,
Javier R. Vignote,
R. Schiavilla
[show abstract]
[hide abstract]
ABSTRACT: We have measured the 4He(e,e'p)3H reaction at missing momenta of 130-300 MeV/c using the three-spectrometer facility at the Mainz microtron MAMI. Data were taken in perpendicular kinematics to allow us to determine the response function Rlt and the asymmetry term Atl. The data are compared to both relativistic and non-relativistic calculations.
09/2004;
-
A. Kozlov,
A. J. Sarty,
K. A. Aniol,
P. Bartsch,
D. Baumann,
W. Bertozzi, K. Bohinc,
R. Bohm,
J. P. Chen,
D. Dale,
L. Dennis,
S. Derber
[show abstract]
[hide abstract]
ABSTRACT: New, high-precision measurements of the 3He(e,e'p) reaction using the A1
collaboration spectrometers at the Mainz microtron MAMI are presented. These
were performed in antiparallel kinematics at energy transfers below the
quasi-elastic 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 Plane Wave Impulse
Approximation were observed in both the two- and three-body breakup channels.
Full Faddeev-type calculations account for some of the observed excess cross
section, but significant differences remain.
Physical Review Letters - PHYS REV LETT. 01/2004; 93(13).
-
P Bartsch,
D Baumann,
J Bermuth,
R Böhm, K Bohinc,
D Bosnar,
M Ding,
M Distler,
D Drechsel,
D Elsner, [......],
Th Pospischil,
M Potokar,
G Rosner,
H Schmieden,
M Seimetz,
A Süle,
L Tiator,
A Wagner,
Th Walcher,
M Weis
[show abstract]
[hide abstract]
ABSTRACT: In a p((-->)e,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.
Physical Review Letters 04/2002; 88(14):142001. · 7.37 Impact Factor
-
H Merkel,
P Bartsch,
D Baumann,
J Bermuth,
A M Bernstein, K Bohinc,
R Böhm,
N Clawiter,
S Derber,
M Ding, [......],
M M Pavan,
Th Pospischil,
M Potokar,
G Rosner,
H Schmieden,
M Seimetz,
S Sirca,
A Wagner,
Th Walcher,
M Weis
[show abstract]
[hide abstract]
ABSTRACT: New data are presented on the p(e,e'p)pi(0) reaction at threshold at a four-momentum transfer of Q(2) = 0.05 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 epsilon, the structure functions sigma(T), sigma(L), sigma(TT), and sigma(TL) are determined. The results are compared with calculations in heavy baryon chiral perturbation theory and with a phenomenological model. The measured cross section is significantly smaller than both predictions.
Physical Review Letters 02/2002; 88(1):012301. · 7.37 Impact Factor
-
P. Bartsch,
D. Baumann,
J. Bermuth,
R. Boehm, K. Bohinc,
D. Bosnar,
M Ding,
M. Distler,
D. Drechsel,
D Elsner, [......],
Th. Pospischil,
M. Potokar,
G Rosner,
H. Schmieden,
M. Seimetz,
A. Suele,
L. Tiator,
A Wagner,
Th. Walcher,
M. Weis
[show abstract]
[hide abstract]
ABSTRACT: In a p(e_pol,e'p)pi_0 out-of-plane coincidence experiment at the 3-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 lack of understanding of the non-resonant background, which in dynamical models is related to the pion cloud. Comment: 5 pages, 2 figures, 2 tables
12/2001;
-
G. Kubon,
H. Anklin,
P. Bartsch,
D. Baumann,
W. U. Boeglin, K. Bohinc,
R. Boehm,
C. Carasco,
M. O. Distler,
I. Ewald, [......],
I. Sick,
S. Sirca,
Ph. Trueb,
A Wagner,
Th. Walcher,
G. Warren,
M. Weis,
H. Woehrle,
M. ZeierJ. Zhao,
B. Zihlmann
[show abstract]
[hide abstract]
ABSTRACT: Precise data on the neutron magnetic form factor G_{mn} have been obtained with measurements of the ratio of cross sections of D(e,e'n) and D(e,e'p) up to momentum transfers of Q^2 = 0.9 (GeV/c)^2. Data with typical uncertainties of 1.5% are presented. These data allow for the first time to extract a precise value of the magnetic radius of the neutron. Comment: 10 pages, 2 figures, submitted to Physics Letters B
07/2001;
-
T Pospischil,
P Bartsch,
D Baumann,
J Bermuth,
R Böhm, K Bohinc,
S Derber,
M Ding,
M Distler,
D Drechsel, [......],
H Schmieden,
M Seimetz,
S Sirca,
I Sick,
A Süle,
L Tiator,
A Wagner,
T Walcher,
G A Warren,
M Weis
[show abstract]
[hide abstract]
ABSTRACT: The recoil proton polarization has been measured in the p(e-->,e'p-->)pi(0) reaction in parallel kinematics around W = 1232 MeV, Q2 = 0.121 (GeV/c)2, and epsilon = 0.718 using the polarized cw electron beam of the Mainz Microtron. All three proton polarization components, Px/P(e) = (-11.4+/-1.3+/-1.4)%, P(y) = (-43.1+/-1.3+/-2.2)%, and P(z)/P(e) = (56.2+/-1.5+/-2.6)%, could be measured simultaneously. The Coulomb quadrupole to magnetic dipole ratio, CMR = (-6.4+/-0.7(stat)+/-0.8(syst))%, was determined from Px in the framework of the Mainz Unitary Isobar Model. The consistency among the reduced polarizations and the extraction of the ratio of longitudinal-to-transverse response is discussed.
Physical Review Letters 04/2001; 86(14):2959-62. · 7.37 Impact Factor
-
Th. Pospischil,
P. Bartsch,
D. Baumann,
R. Böhm, K. Bohinc,
M. Ding,
S. Derber,
M.O. Distler,
D. Elsner,
I. Ewald, [......],
J. Sanner,
H. Schmieden,
M. Seimetz,
S. Širca,
I. Sick,
O. Strähle,
A. Süle,
A. Wagner,
Th. Walcher,
M. Weis
[show abstract]
[hide abstract]
ABSTRACT: 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.
European Physical Journal A 01/2001; 12(1):125-127. · 2.19 Impact Factor
-
Th. Pospischil,
P. Bartsch,
D. Baumann,
J. Bermuth,
R. Boehm, K. Bohinc,
S. Derber,
M Ding,
M. Distler,
D. Drechsel, [......],
H. Schmieden,
M. Seimetz,
S. Sirca,
I. Sick,
A. Suele,
L. Tiator,
A Wagner,
Th. Walcher,
G.A. Warren,
M. Weis
[show abstract]
[hide abstract]
ABSTRACT: The recoil proton polarization has been measured in the p (\vec e,e'\vec p) pi^0 reaction in parallel kinematics around W = 1232 MeV, Q^2 = 0.121 (GeV/c)^2 and epsilon = 0.718 using the polarized c.w. electron beam of the Mainz Microtron. Due to the spin precession in a magnetic spectrometer, all three proton polarization components P_x/P_e = (-11.4 \pm 1.3 \pm 1.4) %, P_y = (-43.1 \pm 1.3 \pm 2.2) %, and P_z/P_e = (56.2 \pm 1.5 \pm 2.6) % could be measured simultaneously. The Coulomb quadrupole to magnetic dipole ratio CMR = (-6.4\pm 0.7_{stat}\pm 0.8_{syst}) % was determined from P_x in the framework of the Mainz Unitary Isobar Model. The consistency among the reduced polarizations and the extraction of the ratio of longitudinal to transverse response is discussed.
12/2000;
-
S Dieterich,
P. Bartsch,
D. Baumann,
J. Bermuth, K. Bohinc,
R Böhm,
D. Bosnar,
S. Derber,
M Ding,
M. Distler, [......],
H. Schmieden,
M. Seimetz,
I. Sick,
S Strauch,
J. M. Udias,
J. R. Vignote,
A Wagner,
Th. Walcher,
G. Warren,
M. Weis
[show abstract]
[hide abstract]
ABSTRACT: Polarization transfer in the 4He(e,e'p)3H reaction at a Q^2 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. Comment: 5 pages, Latex, 2 postscript figures, submitted to Physics Letters B
11/2000;
-
Th. Pospischil,
P. Bartsch,
D. Baumann,
R. Böhm, K. Bohinc,
N. Clawiter,
M. Ding,
S. Derber,
M. Distler,
D. Elsner, [......],
H. Schmieden,
M. Seimetz,
I. Sick,
O. Strähle,
A. Süle,
A. Wagner,
Th. Walcher,
G.A. Warren,
M. Weis,
X.-Q. Wu
[show abstract]
[hide abstract]
ABSTRACT: For experiments the 3-spectrometer setup of the A1 collaboration at MAMI has been supplemented by a focal plane proton-polarimeter. To this end, a carbon analyzer of variable thickness and two double-planes of horizontal drift chambers have been added to the standard detector system of Spectrometer A. Due to the spin precession in the spectrometer magnets, all three polarization components at the target can be measured simultaneously. The performance of the polarimeter has been studied using elastic scattering.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 10/2000;
-
R. E. J. Florizone,
W. Bertozzi,
J P Chen,
D Dale,
S Gilad,
A. J. Sarty,
J.A. Templon,
S. P. Van Verst,
J Zhao,
Z L Zhou, [......],
Th. Walcher,
K. A. Aniol,
M.B. Epstein,
D J Margaziotis,
M. Kuss,
A Richter,
G. Schrieder, K. Bohinc,
M. Potokar,
S. Širca
[show abstract]
[hide abstract]
ABSTRACT: Precision studies of the reaction $^{3}$He(e,e$^\prime$p) using the three-spectrometer facility at the Mainz microtron MAMI are presented. All data are for quasielastic kinematics at $|\vec{q} | =685$ MeV/c. Absolute cross sections were measured at three electron kinematics. For the measured missing momenta range from 10 to 165 MeV/c, no strength is observed for missing energies higher than 20 MeV. Distorted momentum distributions were extracted for the two-body breakup and the continuum. The longitudinal and transverse behavior was studied by measuring the cross section for three photon polarizations. The longitudinal and transverse nature of the cross sections is well described by a currently accepted and widely used prescription of the off-shell electron-nucleon cross-section. The results are compared to modern three-body calculations and to previous data.
09/1999;
-
P. Bartsch,
D. Baumann,
J. Bermuth, K. Bohinc,
R. Böhm,
D. Bosnar,
N. Clawiter,
S. Derber,
M. Ding,
M.O. Distler, [......],
T. Pospischil,
M. Potokar,
D. Rohe,
G. Rosner,
H. Schmieden,
S. Širca,
A. Wagner,
T. Walcher,
M. Weis,
S. Wolf
[show abstract]
[hide abstract]
ABSTRACT: 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.
European Physical Journal A 01/1999; 4(3):209-216. · 2.19 Impact Factor
-
S. Dieterich,
P. Bartsch,
D. Baumann,
J. Bermuth, K. Bohinc,
R. Böhm,
D. Bosnar,
S. Derber,
M. Ding,
M. Distler, [......],
H. Schmieden,
M. Seimetz,
I. Sick,
S. Strauch,
J.M. Udias,
J.R. Vignote,
A. Wagner,
Th. Walcher,
G. Warren,
M. Weis
[show abstract]
[hide abstract]
ABSTRACT: Polarization transfer in the 4HeH 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.
Physics Letters B.
-
P. Bartsch,
D. Baumann,
J. Bermuth,
R. Bohm, K. Bohinc,
D. Bosnar,
M Ding,
M. Distler,
D. Drechsel,
D Elsner, [......],
T Pospischil,
M. Potokar,
G Rosner,
H. Schmieden,
M. Seimetz,
A. Sule,
L. Tiator,
A Wagner,
T Walcher,
M. Weis
[show abstract]
[hide abstract]
ABSTRACT: 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.
-
S Dieterich,
P. Bartsch,
D. Baumann,
J. Bermuth, K. Bohinc,
R. Bohm,
D. Bosnar,
S. Derber,
M Ding,
M. Distler, [......],
H. Schmieden,
M. Seimetz,
I. Sick,
S Strauch,
J. M. Udias,
J. R. Vignote,
A Wagner,
Th. Walcher,
G. Warren,
M. Weis
[show abstract]
[hide abstract]
ABSTRACT: Polarization transfer in the<sup>4</sup>He(e,e'p)<sup>3</sup>H reaction at a Q<sup>2</sup> of 0.4 (GeV/c)<sup>2</sup> 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.
