-
W. U. Boeglin,
H Arenhövel,
K. I. Blomqvist,
R Böhm, M. Distler,
R Edelhoff,
I. Ewald,
R. Florizone,
J. Friedrich,
R Geiges, [......],
A. Rokavec,
G Rosner,
P. Sauer,
I. Sick,
S. Sirca S. Schardt,
A. Serdarevic,
B. Vodenik,
A Wagner,
Th. Walcher,
S Wolf
[show abstract]
[hide abstract]
ABSTRACT: The interference response function f_LT (R_LT) of the D(e,e'p)n reaction has been determined at squared four-momentum transfer Q^2 = 0.33 (GeV/c)^2 and for missing momenta up to p_miss= 0.29 (GeV/c). The results have been compared to calculations that reproduce f_LT quite well but overestimate the cross sections by 10 - 20% for missing momenta between 0.1 (GeV/c) and 0.2 (GeV/c) .
05/2008;
-
P. Janssens,
L. Van Hoorebeke,
H. Fonvieille,
N D'Hose,
P Y Bertin,
I. Bensafa,
N. Degrande, M. Distler,
R. Di Salvo,
L. Doria, [......],
G. Laveissiere,
D. Lhuillier,
D. Marchand,
H. Merkel,
J ROCHE,
G. Tamas,
M. Vanderhaeghen,
R. Van de Vyver,
J. Van de Wiele,
Th. Walcher
[show abstract]
[hide abstract]
ABSTRACT: This paper describes the Monte Carlo simulation developed specifically for the VCS experiments below pion threshold that have been performed at MAMI and JLab. This simulation generates events according to the (Bethe-Heitler + Born) cross section behaviour and takes into account all relevant resolution-deteriorating effects. It determines the `effective' solid angle for the various experimental settings which are used for the precise determination of photon electroproduction absolute cross section.
10/2006;
-
D. Elsner,
A. Süle,
P. Barneo,
P. Bartsch,
D. Baumann,
J. Bermuth,
R. Böhm,
D. Bosnar,
M. Ding, M. Distler, [......],
R. Neuhausen,
Th. Pospischil,
M. Potokar,
G. Rosner,
H. Schmieden,
M. Seimetz,
O. Strähle,
L. Tiator,
Th. Walcher,
M. Weis
[show abstract]
[hide abstract]
ABSTRACT: The reaction p(e, e'p)π0 has been studied at Q2 = 0.2 (GeV/c)2 in the region of W = 1232MeV. From measurements left and right of
[(q)\vec] \vec{q}\,
, cross-section asymmetries ρLT have been obtained in forward kinematics ρLT(
qp0cm \theta_{{\pi^0}}^{{cm}}
= 20°) = (- 11.68±2.36stat±2.36sys) and backward kinematics ρLT(
qp0cm \theta_{{\pi^0}}^{{cm}}
= 160°) = (12.18±0.27stat±0.82sys) π0. Multipole ratios
 \Re
{S1+ * M1+}/| M1+|2 and
 \Re
{S0+ * M1+}/| M1+|2 were determined in the framework of the MAID2003 model. The results are in agreement with older data. The unusally strong
negative
 \Re
{S0+ * M1+}/| M1+|2 required to bring also the result of Kalleicher et al. in accordance with the rest of the data is almost excluded.
European Physical Journal A 12/2005; 27(1):91-97. · 2.19 Impact Factor
-
D Elsner,
A. Süle,
P Barneo,
P. Bartsch,
D. Baumann,
J. Bermuth,
R Böhm,
D. Bosnar,
M Ding, M. Distler, [......],
U Müller,
R. Neuhausen,
Th. Pospischil,
M. Potokar,
G Rosner,
H. Schmieden,
M. Seimetz O. Strähle,
L. Tiator,
Th. Walcher,
M. Weis
[show abstract]
[hide abstract]
ABSTRACT: The reaction p(e,e'p)pi^0 has been studied at Q^2=0.2 (GeV/c)^2 in the region of W=1232 MeV. From measurements left and right of q, cross section asymmetries \rho_LT have been obtained in forward kinematics \rho_LT(\theta_\pi^0=20deg) = (-11.68 +/- 2.36_stat +/- 2.36_sys)$ and backward kinematics \rho_LT(\theta_\pi^0=160deg) =(12.18 +/- 0.27_stat +/- 0.82_sys). Multipole ratios \Re(S_1+^* M_1+)/|M_1+|^2 and \Re(S_0+^* M_1+)/|M_1+|^2 were determined in the framework of the MAID2003 model. The results are in agreement with older data. The unusally strong negative \Re(S_0+^* M_1+)/|M_1+|^2 required to bring also the result of Kalleicher et al. in accordance with the rest of the data is almost excluded. Comment: 7 pages, 7 figures, 4 tables. Changed content. Accepted for publication in EPJA
07/2005;
-
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
-
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;
-
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,
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;
-
K. I. Blomqvist,
W. U. Boeglin,
R. Bohm, M. Distler,
R Edelhoff,
J. Friedrich,
R Geiges,
P. Jennewein,
M. Kahrau,
M. Korn, [......],
H. Merkel,
K. Merle,
U Muller,
R. Neuhausen,
P. Sauer,
S Schardt,
H. Schmieden,
A Wagner,
Th. Walcher,
S Wolf
[show abstract]
[hide abstract]
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 MeV/c and 550 MeV/c, respectively. The spectrometer B has a solid angle of 5.6 msr and a somewhat reduced momentum acceptance of 15%, but it reaches a maximum momentum larger than that of the MAMI electron beam (855 MeV/c). It consists of a single clamshell dipole magnet with point-to-point optics in both planes. Each spectrometer is equipped with a position sen...
10/1997;
-
K. I. Blomqvist,
W. U. Boeglin,
R. Bohm, M. Distler,
R Edelhoff,
J. Friedrich,
R Geiges,
M. Kahrau,
S. Kamalov,
M. Kirchbach, [......],
A. Liesenfeld,
K. Merle,
R. Neuhausen,
M. Potokar,
A Richter,
G Rosner,
P. Sauer,
St. Schardt,
G. Schrieder,
St. Wolf
[show abstract]
[hide abstract]
ABSTRACT: The differential coincident pion electroproduction cross section in the 3 He(e,e 0 ß + ) 3 H reaction has been measured with high resolution with the threespectrometer set-up at the Mainz Microtron (MAMI) electron accelerator. Present address: Research Center for Nuclear Physics, Osaka Daigaku, 10-1 Mihogaoka, Ibaraki, Osaka 567, Japan y Corresponding author. E-mail richter@linac.ikp.physik.th-darmstadt.de 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 standard Born-amplitudes and also delta and higher resonance terms. Threebody Fadeev wave functions are used and...
08/1997;
-
K. I. Blomqvist,
W. U. Boeglin,
R. Böhm, M. Distler,
D. Drechsel,
R. Edelhoff,
J. Friedrich,
R. Geiges,
O. Hanstein,
M. Kahrau, [......],
G. Rosner,
P. Sauer,
S. Schardt,
H. Schmieden,
S. Sirca,
L. Tiator,
B. Vodenik,
A. Wagner,
Th. Walcher,
S. Wolf
[show abstract]
[hide abstract]
ABSTRACT: The reactione+p > e+
++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.
Zeitschrift für Physik A Hadrons and Nuclei 01/1996; 353(4):415-421.
-
K. I. Blomqvist,
W. U. Boeglin,
R. Böhm, M. Distler,
R. Edelhoff,
J. Friedrich,
R. Geiges,
M. Kahrau,
M. Korn,
H. Kramer, [......],
A. Rokavec,
G. Rosner,
P. Sauer,
S. Schardt,
A. Serdarević,
Th. Veit,
B. Vodenik,
A. Wagner,
Th. Walcher,
S. Wolf
[show abstract]
[hide abstract]
ABSTRACT: The12C(e, e'p)11B
g.s
reaction has been measured in parallel and anti-parallel kinematics over ap
m range of –120p
mT
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 (=0.98(5)). The spectroscopic factor for this transition as determined with the new Mainz data (S
=1.54(5)) is 22% smaller than the NIKHEF value.
Zeitschrift für Physik A Hadrons and Nuclei 11/1995; 351(4):353-354.
-
T. Veit,
K. I. Blomqvist,
W. U. Boeglin, M. Distler,
R. Edelhoff,
J. Friedrich,
R. Geiges,
M. Korn,
H. Kramer,
K. W. Krygier, [......],
R. Neuhausen,
E. A. J. M. Offermann,
Th. Pospischil,
A. W. Richter,
G. Rosner,
P. Sauer,
S. Schardt,
A. Wagner,
Th. Walcher,
S. Wolf
[show abstract]
[hide abstract]
ABSTRACT: 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, ep)11Bg.s.) in the quasi-free region.
Zeitschrift für Physik A Hadrons and Nuclei 05/1994; 349(2):161-168.
-
K.I. Blomqvist,
W.U. Boeglin,
R. Böhm, M. Distler,
R. Edelhoff,
J. Friedrich,
R. Geiges,
M. Kahrau,
M. Korn,
H. Kramer, [......],
A. Rokavec,
G. Rosner,
P. Sauer,
S. Schardt,
A. Serdarević,
Th. Veit,
B. Vodenik,
A. Wagner,
Th. Walcher,
S. Wolf
[show abstract]
[hide abstract]
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 < pm < 700 MeV/c. The reduced cross sections are compared to DWIA calculations in which the proton in its initial state is assumed to be bound in the mean field of a Woods-Saxon well. At low momenta, our results at Tp = 93 MeV are in excellent agreement with a measurement performed at NIKHEF. At high momenta the rise above the mean-field prediction is modest.
Physics Letters B. 344:85-90.
-
S. Kerhoas,
P. Bartsch,
J. Berthot,
P. Y. Bertin,
V. Breton,
W. U. Boeglin,
R. Böhm,
N. D'Hose,
T. Caprano,
S. Derber, [......],
G. Tamas,
M. Tytgat,
M. Vanderhaeghen,
L. van Hoorebeke,
R. van de Vyver,
J. van de Wiele,
P. Vernin,
A. Wagner,
Th. Walcher,
S. Wolf
-1:523.
-
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.
-
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.
-
S. Kerhoas,
P. Bartsch,
J Berthot,
P Y Bertin,
V. Breton,
W. U. Boeglin,
R. Bohm,
N D'Hose,
T. Caprano,
S. Derber, [......],
S Schardt,
G. Tamas,
M. Tytgat,
M. Vanderhaeghen,
L. Van Hoorebeke,
R. Van de Vyver,
J. Van de Wiele,
P. Vernin,
A Wagner,
T Walcher
[show abstract]
[hide abstract]
ABSTRACT: Virtual Compton scattering, i.e. the exclusive reaction gamma *p to gamma 'p' with gamma * denoting a virtual photon, provides new insights on the internal structure of the proton. Below pi /sup 0/ production threshold, this experiment measures the generalized polarizabilities of the proton as defined by Guichon and Drechsel. These new electromagnetic observables, functions of Q/sup 2/, enlarge the concept of electric ( alpha ) and magnetic ( beta ) polarizabilities in real Compton scattering (Q/sup 2/=0). The first VCS experiment of this kind was measured at the three spectrometer facility at the Mainz Microtron MAMI for Q/sup 2/=0.33 GeV/sup 2/ and we present in this paper the preliminary results.
