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H Dutz,
K Helbing,
J Krimmer,
T Speckner, G Zeitler,
J Ahrens,
S Altieri,
J R M Annand,
G Anton,
H-J Arends, [......],
C Rohlof,
T Rostomyan,
M Sauer,
B Schoch,
M Schumacher,
G Tamas,
A Thomas,
R van de Vyver,
W Weihofen,
F Zapadtka
[show abstract]
[hide abstract]
ABSTRACT: Helicity-dependent total photoabsorption cross sections on the deuteron have been measured for the first time at ELSA (Bonn) in the photon energy range from 815 to 1825 MeV. Circularly polarized tagged photons impinging on a longitudinally polarized LiD target have been used together with a highly efficient 4pi detector system. The data around 1 GeV are not compatible with predictions from existing multipole analyses. From the measured energy range an experimental contribution to the GDH integral on the neutron of [33.9 +/- 5.5(stat) +/- 4.5(syst)] microb is extracted.
Physical Review Letters 05/2005; 94(16):162001. · 7.37 Impact Factor
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H Dutz,
K Helbing,
J Krimmer,
T Speckner, G Zeitler,
J Ahrens,
S Altieri,
J R M Annand,
G Anton,
H-J Arends, [......],
C Rohlof,
T Rostomyan,
M Sauer,
B Schoch,
M Schumacher,
G Tamas,
A Thomas,
R van de Vyver,
W Weihofen,
F Zapadtka
[show abstract]
[hide abstract]
ABSTRACT: For the first time we checked the fundamental Gerasimov-Drell-Hearn (GDH) sum rule for the proton experimentally in the photon energy range from 0.2-2.9 GeV with the tagged photon facilities at MAMI (Mainz) and ELSA (Bonn). New data of the doubly polarized total cross section difference are presented in the energy range from 1.6 to 2.9 GeV. The contribution to the GDH integral from 0.2-2.9 GeV yields [254+/-5(stat)+/-12(syst)] microb with negative contributions in the Regge regime at photon energies above 2.1 GeV. This trend supports the validity of the GDH sum rule.
Physical Review Letters 08/2004; 93(3):032003. · 7.37 Impact Factor
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H Dutz,
K Helbing,
J Krimmer,
T Speckner, G Zeitler,
J Ahrens,
S Altieri,
J R M Annand,
G Anton,
H-J Arends, [......],
C Rohlof,
T Rostomyan,
M Sauer,
B Schoch,
M Schumacher,
G Tamas,
A Thomas,
R van de Vyver,
W Weihofen,
F Zapadtka
[show abstract]
[hide abstract]
ABSTRACT: To verify the fundamental Gerasimov-Drell-Hearn (GDH) sum rule for the first time experimentally, we measured the helicity dependent total photoabsorption cross section with circularly polarized real photons and longitudinally polarized nucleons in the photon energy range 0.68-1.82 GeV with the tagged photon facility at ELSA. The experiment was carried out with a 4pi detection system, a circularly polarized tagged photon beam, and a frozen spin polarized proton target. The contribution to the GDH sum rule in this photon energy range is [49.9+/-2.4(stat)+/-2.2(syst)] microb.
Physical Review Letters 12/2003; 91(19):192001. · 7.37 Impact Factor
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The GDH and Collaborations,
J. Ahrens,
S. Altieri,
J.R.M. Annand,
G. Anton,
H.-J. Arends,
K. Aulenbacher,
R. Beck,
C. Bradtke,
A. Braghieri, [......],
T. Speckner,
N. Takabayashi,
G. Tamas,
A. Thomas,
R. van de Vyver,
A. Wakai,
W. Weihofen,
F. Wissmann,
F. Zapadtka, G. Zeitler
[show abstract]
[hide abstract]
ABSTRACT: The helicity dependence of the γ
p↦pη reaction has been measured for the first time at a center-of-mass angle θ*
η = 70° in the photon energy range from 780 MeV to 790 MeV. The experiment, performed at the Mainz microtron MAMI, used a 4π-detector
system, a circularly polarized, tagged photon beam, and a longitudinally polarized frozen-spin target. The helicity 3/2 cross-section
is found to be small and the results for helicity 1/2 agree with predictions from the MAID analysis.
European Physical Journal A 05/2003; 17(2):241-244. · 2.19 Impact Factor
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J Ahrens,
S Altieri,
J R M Annand,
G Anton,
H-J Arends,
K Aulenbacher,
R Beck,
C Bradtke,
A Braghieri,
N Degrande, [......],
N Takabayashi,
G Tamas,
A Thomas,
L Tiator,
R Van Vyver,
A Wakai,
W Weihofen,
F Wissmann,
F Zapadtka, G Zeitler
[show abstract]
[hide abstract]
ABSTRACT: The helicity dependence of the gamma-->p-->-->ppi(0) reaction has been measured for the first time in the photon-energy range from 550 to 790 MeV. The experiment, performed at the Mainz microtron MAMI, used a 4pi-detector system, a circularly polarized, tagged photon beam, and a longitudinally polarized frozen-spin target. These data are predominantly sensitive to the D13(1520) resonance and are used to determine its helicity amplitudes.
Physical Review Letters 07/2002; 88(23):232002. · 7.37 Impact Factor
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J. Naumann,
G. Anton,
A. Bock,
P. Grabmayr,
K. Helbing,
B. Kiel,
D. Menze,
T. Michel,
S. Proff,
M. Sauer,
M. Schumacher,
T. Speckner,
W. Weihofen, G. Zeitler
[show abstract]
[hide abstract]
ABSTRACT: This paper describes the set-up and calibration of the tagging system of the GDH-Experiment at the accelerator facility Elsa in Bonn. The system consists of a C-type dipole magnet and a hodoscope of 65 scintillation counters which are operated pairwise in coincidence to form 64 tagging channels. Photons can be tagged in a range of 68–97% of the primary electron energy E0. The energy resolution ranges from 0.2% to 0.6% of E0. The time resolution is better than . The system was operated at rates up to in the full tagged energy range. The energy dependence of the photon definition probability was determined using several different methods and was found to agree well with calculations.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment.
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J. Ahrens,
S Altieri,
J. R. M. Annand,
G. Anton,
H.J. Arends,
K. Aulenbacher,
R. Beck,
C. Bradtke,
A. Braghieri,
N. Degrande, [......],
N Takabayashi,
G. Tamas,
A Thomas,
L. Tiator,
R. Van de Vyver,
A. Wakai,
W. Weihofen,
F. Wissmann,
F. Zapadtka, G. Zeitler
[show abstract]
[hide abstract]
ABSTRACT: A high-quality double-polarization data set for the helicity dependence of the total and differential cross-sections for both γp→Nπ channels in the Δ region has been obtained in the framework of the GDH experiment. The experiment, performed at the Mainz microtron MAMI, used a 4 π detection system, a circularly polarized photon beam, and a longitudinally polarized frozen-spin target. These data are included in the database to perform a multipole analysis to determine the properties of the Δ(1232) -resonance. For the resonant Δ(1232) multipoles we find a very good agreement with previous analyses, while the nonresonant ones show significant deviations.
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J. Ahrens,
S Altieri,
J. R. M. Annand,
G. Anton,
H.J. Arends,
K. Aulenbacher,
R. Beck,
C. Bradtke,
A. Braghieri,
N. Degrande, [......],
T. Speckner,
N Takabayashi,
G. Tamas,
A Thomas,
R. Van de Vyver,
A. Wakai,
W. Weihofen,
F. Wissmann,
F. Zapadtka, G. Zeitler
[show abstract]
[hide abstract]
ABSTRACT: The helicity dependence of the total cross section for the γp→pπ<sup>0</sup>π<sup>0</sup> reaction has been measured for the first time at incident photon energies from 400 to 800 MeV. The measurement, performed at the tagged photon beam facility of the MAMI accelerator in Mainz, used the large acceptance detector DAPHNE and a longitudinally polarized frozen-spin target. This channel is found to be excited predominantly when the photon and proton have a parallel spin orientation, most likely due to the intermediate production of the D<sub>13</sub>(1520) resonance. However, the contribution of the antiparallel spin configuration, arising from other reaction mechanisms, is also not negligible. This result gives important new information to resolve the existing model discrepancies in the identification of the nucleon resonances contributing to this channel.
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J. Ahrens,
S. Altieri,
J.R.M. Annand,
G. Anton,
H.-J. Arends,
K. Aulenbacher,
R. Beck,
C. Bradtke,
A. Braghieri,
N. Degrande, [......],
T. Speckner,
N. Takabayashi,
G. Tamas,
A. Thomas,
R. van de Vyver,
A. Wakai,
W. Weihofen,
F. Wissmann,
F. Zapadtka, G. Zeitler
[show abstract]
[hide abstract]
ABSTRACT: The helicity dependence of the total cross section for the reaction has been measured for the first time at incident photon energies from 400 to 800 MeV. The measurement, performed at the tagged photon beam facility of the MAMI accelerator in Mainz, used the large acceptance detector DAPHNE and a longitudinally polarized frozen-spin target. This channel is found to be excited predominantly when the photon and proton have a parallel spin orientation, most likely due to the intermediate production of the D13(1520) resonance. However, the contribution of the antiparallel spin configuration, arising from other reaction mechanisms, is also not negligible. This result gives important new information to resolve the existing model discrepancies in the identification of the nucleon resonances contributing to this channel.
Physics Letters B.
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J Ahrens,
S Altieri,
J.R.M Annand,
G Anton,
H.-J Arends,
K Aulenbacher,
R Beck,
C Bradtke,
A Braghieri,
N Degrande, [......],
T Speckner,
N Takabayashi,
G Tamas,
A Thomas,
R van de Vyver,
A Wakai,
W Weihofen,
F Wissmann,
F Zapadtka, G Zeitler
[show abstract]
[hide abstract]
ABSTRACT: The helicity dependence of the total cross section for the reaction has been measured for the first time at incident photon energies from 400 to 800 MeV. The measurement was performed with the large acceptance detector DAPHNE at the tagged photon beam facility of the MAMI accelerator in Mainz. This channel is found to be excited predominantly when the photon and proton have a parallel spin orientation, due to the intermediate production of the D13 resonance.
Physics Letters B.
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[show abstract]
[hide abstract]
ABSTRACT: For the GDH-Experiment at ELSA, the helicity dependent total photoabsorption cross-section is to be determined. These measurements will be performed with the newly developed GDH-Detector which is presented here. The concept of the GDH-Detector is to detect at least one reaction product from all possible hadronic processes with almost complete acceptance concerning solid angle and efficiency. This is realized by an arrangement of scintillators and lead. The overall acceptance for hadronic processes is better than 99%. The electromagnetic background is suppressed by about five orders of magnitude by means of a threshold Cherenkov detector. In dedicated tests, it has been demonstrated that all individual components of the GDH-Detector fulfill the design goals. Measurements of unpolarized total photoabsorption cross-sections were performed to ensure that the complete GDH-Detector is operational.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 484:129-139. · 1.21 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Active collimators are designed to both collimate the tagged photon beam and suppress the background of secondary photons. These secondary photons are generated by interaction processes in the collimator medium. They may reach the hadron target with a lower energy compared to the energy determined by the tagging system. Accordingly, those events are tagged with a wrong energy and have to be rejected. By means of a Monte Carlo simulation we investigated the effect and the performance of an active collimator system and developed an optimal design of the collimators to prepare a clean high-energy photon beam. The resulting set-up ensures a precise determination of the tagging efficiency and of the photon flux. The active collimators are a necessary tool to correctly determine photoproduction cross-sections. Results of test measurements at ELSA in Bonn, and MAMI B in Mainz are discussed. Special interest is given to the use of the active collimators in the experiment to test the GDH sum rule at ELSA up to .
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 459:6-15. · 1.21 Impact Factor
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J. Ahrens,
S Altieri,
J. R. M. Annand,
G. Anton,
H.J. Arends,
K. Aulenbacher,
R. Beck,
C. Bradtke,
A. Braghieri,
N D'Hose, [......],
T. Speckner,
N Takabayashi,
G. Tamas,
A Thomas,
R. Van de Vyver,
A. Wakai,
W. Weihofen,
F. Wissmann,
F. Zapadtka, G. Zeitler
[show abstract]
[hide abstract]
ABSTRACT: The helicity dependence of the gamma p to p eta reaction has been measured for the first time at a center-of-mass angle theta /sub eta //sup */=70 degrees in the photon energy range from 780 MeV to 790 MeV. The experiment, performed at the Mainz microtron MAMI, used a 4 pi -detector system, a circularly polarized, tagged photon beam, and a longitudinally polarized frozen-spin target. The helicity 3/2 cross-section is found to be small and the results for helicity 1/2 agree with predictions from the MAID analysis.
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J. Ahrens,
S Altieri,
J. R. M. Annand,
G. Anton,
H.J. Arends,
K. Aulenbacher,
R. Beck,
C. Bradtke,
A. Braghieri,
N. Degrande, [......],
M. Steigerwald,
N Takabayashi,
G. Tamas,
A Thomas,
R. Van de Vyver,
A. Wakai,
W. Weihofen,
F. Wissmann,
F. Zapadtka, G. Zeitler
[show abstract]
[hide abstract]
ABSTRACT: A direct measurement of the helicity dependence of the total photoabsorption cross section an the proton was carried out at MAMI (Mainz) in the energy range 200 lt E-[gamma] lt 800 MeV. The experiment used a 4[pi] detection system, a circularly polarized. tagged photon beam, and a frozen spin target. The contributions to the Gerasimov-Drell-Hearn sum rule and to the forward spin polarizability gamma (0) determined from the data are 226 +/- 5(stat) +/- 12(syst) mub and -187 +/- 8(stat) +/- 10(syst) x 10(-6) fm(4), respectively, for 200 lt E-[gamma] lt 800 MeV.
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J. Ahrens,
S Altieri,
J. R. M. Annand,
G. Anton,
H.J. Arends,
K. Aulenbacher,
R. Beck,
C. Bradtke,
A. Braghieri,
N. Degrande, [......],
N Takabayashi,
G. Tamas,
A Thomas,
L. Tiator,
R. Van Vyver,
A. Wakai,
W. Weihofen,
F. Wissmann,
F. Zapadtka, G. Zeitler
[show abstract]
[hide abstract]
ABSTRACT: The helicity dependence of the (γ) over right arrow(p) over right arrow →ppi(0) reaction has been measured for the first time in the photon-energy range from 550 to 790 MeV. The experiment, performed at the Mainz microtron MAMI, used a 4pi - detector system, a circularly polarized, tagged photon beam, and a longitudinally polarized frozen-spin target. These data are predominantly sensitive to the D-13(1520) resonance and are used to determine its helicity amplitudes.
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J. Ahrens,
S Altieri,
J. R. M. Annand,
G. Anton,
H.J. Arends,
K. Aulenbacher,
R. Beck,
C. Bradtke,
A. Braghieri,
N. Degrande, [......],
T. Speckner,
N Takabayashi,
G. Tamas,
A Thomas,
R. Van de Vyver,
A. Wakai,
W. Weihofen,
F. Wissmann,
F. Zapadtka, G. Zeitler
[show abstract]
[hide abstract]
ABSTRACT: The helicity dependence of the total cross section for the gamma p to n pi /sup +/ pi /sup 0/ reaction has been measured for the first time at incident photon energies from 400 to 800 MeV. The measurement was performed with the large acceptance detector DAPHNE at the tagged photon beam facility of the MAMI accelerator in Mainz. This channel is found to be excited predominantly when the photon and proton have a parallel spin orientation, due to the intermediate production of the D/sub 13/ resonance.
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J. Ahrens,
S Altieri,
J. R. M. Annand,
G. Anton,
H.J. Arends,
K. Aulenbacher,
R. Beck,
C. Bradtke,
A. Braghieri,
N. Degrande, [......],
M. Steigerwald,
N Takabayashi,
G. Tamas,
A Thomas,
R. Van de Vyver,
A. Wakai,
W. Weihofen,
F. Wissmann,
F. Zapadtka, G. Zeitler
[show abstract]
[hide abstract]
ABSTRACT: The helicity dependence of the single pion photoproduction on the proton has been measured in the energy range from 200 to 450 MeV for the first time. The experiment, performed at the Mainz microtron MAMI, used a 4 pi-detector system, a circularly polarized, tagged photon beam, and a frozen-spin target. The data obtained provide new information for multipole analyses of pion photoproduction and determine the main contributions to the Gerasimov-Drell-Hearn sum rule and the forward spin polarizability gamma(0).
