-
M. Sudoł,
M. C. Mora Espí,
E. Becheva,
J. Boucher,
T. Hennino,
R. Kunne, D. Marchand,
S. Ong,
B. Ramstein,
J. Van de Wiele,
T. Zerguerras,
F. Maas,
B. Kopf,
M. Pelizaeus,
M. Steinke,
J. Zhong,
E. Tomasi-Gustafsson
[show abstract]
[hide abstract]
ABSTRACT: The possibility of measuring the proton electromagnetic form factors in the time-like region at FAIR with the [`(P)] \overline{{P}}ANDA detector is discussed. Detailed simulations on signal efficiency for the annihilation of [`(p)] \bar{{p}} + p into a lepton pair as well as for the most important background channels have been performed. It is shown that precise measurements
of the differential cross-section of the reaction [`(p)] \bar{{p}} + p
® \rightarrow
e
- + e
+ can be obtained in a wide kinematical range. The determination of the ratio R of the moduli of the electric and magnetic proton form factors will be possible up to a value of momentum transfer squared
of q
2 ≃ 14 (GeV/c)^2 with absolute precision from 0.01 to 0.5 (for R ∼ 1 . The total [`(p)] \bar{{p}} + p
® \rightarrow
e
- + e
+ cross-section will be measured up to q
2 ≃ 28 (GeV/c)^2. The results obtained from simulated events are compared to the existing data. Sensitivity to the two-photon exchange
mechanism is also investigated.
European Physical Journal A 04/2012; 44(3):373-384. · 2.19 Impact Factor
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Collaboration,
D. Androic,
D. S. Armstrong,
J. Arvieux,
R. Asaturyan,
T. D. Averett,
S L Bailey,
G. Batigne,
D. H. Beck,
E. J. Beise, [......],
E. Voutier,
W. F. Vulcan,
S.P. Wells,
G. Warren,
S. E. Williamson,
R. J. Woo,
S. A. Wood,
C Yan,
J Yun,
V. Zeps
[show abstract]
[hide abstract]
ABSTRACT: In the G0 experiment, performed at Jefferson Lab, the parity-violating
elastic scattering of electrons from protons and quasi-elastic scattering from
deuterons is measured in order to determine the neutral weak currents of the
nucleon. Asymmetries as small as 1 part per million in the scattering of a
polarized electron beam are determined using a dedicated apparatus. It consists
of specialized beam-monitoring and control systems, a cryogenic hydrogen (or
deuterium) target, and a superconducting, toroidal magnetic spectrometer
equipped with plastic scintillation and aerogel Cerenkov detectors, as well as
fast readout electronics for the measurement of individual events. The overall
design and performance of this experimental system is discussed.
03/2011;
-
M Sudol,
M. C. Mora Espi,
E. Becheva,
J. Boucher,
T. Hennino,
R. Kunne, D. Marchand,
S. Ong,
B. Ramstein,
J. Van de Wiele,
T. Zerguerras,
F. Maas,
B. Kopf,
M Pelizaeus,
M Steinke,
J Zhong,
E. Tomasi-Gustafsson
[show abstract]
[hide abstract]
ABSTRACT: The possibility of measuring the proton electromagnetic form factors in the time-like region at FAIR with the \PANDA detector is discussed. Detailed simulations on signal efficiency for the annihilation of $\bar p +p $ into a lepton pair as well as for the most important background channels have been performed. It is shown that precision measurements of the differential cross section of the reaction $\bar p +p \to e^++ e^-$ can be obtained in a wide angular and kinematical range. The individual determination of the moduli of the electric and magnetic proton form factors will be possible up to a value of momentum transfer squared of $q^2\simeq 14$ (GeV/c)$^2$. The total $\bar p +p\to e^++e^-$ cross section will be measured up to $q^2\simeq 28$ (GeV/c)$^2$. The results obtained from simulated events are compared to the existing data. Sensitivity to the two photons exchange mechanism is also investigated. Comment: 12 pages, 4 tables, 8 figures Revised, added details on simulations, 4 tables, 9 figures
07/2009;
-
G. Laveissière,
N. Degrande,
S. Jaminion,
C. Jutier,
L. Todor,
R. Di Salvo,
L. Van Hoorebeke,
L. C. Alexa,
B. D. Anderson,
K. A. Aniol, [......],
E. Voutier,
J. W. Watson,
L. B. Weinstein,
K. Wijesooriya,
R. Wilson,
B. B. Wojtsekhowski,
D. G. Zainea,
W.-M. Zhang,
J. Zhao,
Z.-L. Zhou
[show abstract]
[hide abstract]
ABSTRACT: We have made the first measurements of the virtual Compton scattering (VCS) process via the H(e, e'p)γ exclusive reaction in the nucleon resonance region, at backward angles. Results are presented for the W-dependence at fixed Q2=1 GeV2 and for the Q2 dependence at fixed W near 1.5 GeV. The VCS data show resonant structures in the first and second resonance regions. The observed Q2 dependence is smooth. The measured ratio of H(e, e'p)γ to H(e, e'p)π0 cross sections emphasizes the different sensitivity of these two reactions to the various nucleon resonances. Finally, when compared to real Compton scattering (RCS) at high energy and large angles, our VCS data at the highest W (1.8-1.9 GeV) show a striking Q2 independence, which may suggest a transition to a perturbative scattering mechanism at the quark level.
Phys. Rev. C. 01/2009; 79(1).
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D S Armstrong,
J Arvieux,
R Asaturyan,
T Averett,
S L Bailey,
G Batigne,
D H Beck,
E J Beise,
J Benesch,
L Bimbot, [......],
W T H van Oers,
E Voutier,
W Vulcan,
G Warren,
S P Wells,
S E Williamson,
S A Wood,
C Yan,
J Yun,
V Zeps
[show abstract]
[hide abstract]
ABSTRACT: We have measured the beam-normal single-spin asymmetry in elastic scattering of transversely polarized 3 GeV electrons from unpolarized protons at Q2=0.15, 0.25 (GeV/c)2. The results are inconsistent with calculations solely using the elastic nucleon intermediate state and generally agree with calculations with significant inelastic hadronic intermediate state contributions. A(n) provides a direct probe of the imaginary component of the 2gamma exchange amplitude, the complete description of which is important in the interpretation of data from precision electron-scattering experiments.
Physical Review Letters 09/2007; 99(9):092301. · 7.37 Impact Factor
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D. Marchand,
J. Arvieux,
L. Bimbot,
A Biselli,
J. Bouvier,
H. Breuer,
R Clark,
J.C. Cuzon,
M. Engrand,
R. Foglio, [......],
J. Lenoble,
E Liatard,
J Liu,
E. Munoz,
J. Pouxe,
G Quéméner,
B Quinn,
J-S Réal,
O. Rossetto,
R. Sellem
[show abstract]
[hide abstract]
ABSTRACT: The G$^0$ parity-violation experiment at Jefferson Lab (Newport News, VA) is designed to determine the contribution of strange/anti-strange quark pairs to the intrinsic properties of the proton. In the forward-angle part of the experiment, the asymmetry in the cross section was measured for $\vec{e}p$ elastic scattering by counting the recoil protons corresponding to the two beam-helicity states. Due to the high accuracy required on the asymmetry, the G$^0$ experiment was based on a custom experimental setup with its own associated electronics and data acquisition (DAQ) system. Highly specialized time-encoding electronics provided time-of-flight spectra for each detector for each helicity state. More conventional electronics was used for monitoring (mainly FastBus). The time-encoding electronics and the DAQ system have been designed to handle events at a mean rate of 2 MHz per detector with low deadtime and to minimize helicity-correlated systematic errors. In this paper, we outline the general architecture and the main features of the electronics and the DAQ system dedicated to G$^0$ forward-angle measurements. Comment: 35 pages. 17 figures. This article is to be submitted to NIM section A. It has been written with Latex using \documentclass{elsart}. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment In Press (2007)
03/2007;
-
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;
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D S Armstrong,
J Arvieux,
R Asaturyan,
T Averett,
S L Bailey,
G Batigne,
D H Beck,
E J Beise,
J Benesch,
L Bimbot, [......],
W van Oers,
E Voutier,
W Vulcan,
G Warren,
S P Wells,
S E Williamson,
S A Wood,
C Yan,
J Yun,
V Zeps
[show abstract]
[hide abstract]
ABSTRACT: We have measured parity-violating asymmetries in elastic electron-proton scattering over the range of momentum transfers 0.12 < or =Q2 < or =1.0 GeV2. These asymmetries, arising from interference of the electromagnetic and neutral weak interactions, are sensitive to strange-quark contributions to the currents of the proton. The measurements were made at Jefferson Laboratory using a toroidal spectrometer to detect the recoiling protons from a liquid hydrogen target. The results indicate nonzero, Q2 dependent, strange-quark contributions and provide new information beyond that obtained in previous experiments.
Physical Review Letters 09/2005; 95(9):092001. · 7.37 Impact Factor
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G Laveissière,
L Todor,
N. Degrande,
S. Jaminion,
C. Jutier,
R. Di Salvo,
L. Van Hoorebeke,
L.C. Alexa,
B D Anderson,
K. A. Aniol, [......],
E. Voutier,
J. W. Watson,
L B Weinstein,
K. Wijesooriya,
R Wilson,
B. B. Wojtsekhowski,
D.G. Zainea,
W M Zhang,
J Zhao,
Z L Zhou
[show abstract]
[hide abstract]
ABSTRACT: We report a virtual Compton scattering study of the proton at low c.m. energies. We have determined the structure functions P(LL)-P(TT)/epsilon and P(LT), and the electric and magnetic generalized polarizabilities (GPs) alpha(E)(Q2) and beta(M)(Q2) at momentum transfer Q(2)=0.92 and 1.76 GeV2. The electric GP shows a strong falloff with Q2, and its global behavior does not follow a simple dipole form. The magnetic GP shows a rise and then a falloff; this can be interpreted as the dominance of a long-distance diamagnetic pion cloud at low Q2, compensated at higher Q2 by a paramagnetic contribution from piN intermediate states.
Physical Review Letters 10/2004; 93(12):122001. · 7.37 Impact Factor
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F E Maas,
P Achenbach,
K Aulenbacher,
S Baunack,
L Capozza,
J Diefenbach,
K Grimm,
Y Imai,
T Hammel,
D von Harrach, [......],
M Guidal,
R Kunne, D Marchand,
M Morlet,
S Ong,
J van de Wiele,
S Kowalski,
B Plaster,
R Suleiman,
S Taylor
[show abstract]
[hide abstract]
ABSTRACT: We report on a measurement of the parity-violating asymmetry in the scattering of longitudinally polarized electrons on unpolarized protons at a Q2 of 0.230 (GeV/c)(2) and a scattering angle of theta (e) = 30 degrees - 40 degrees. Using a large acceptance fast PbF2 calorimeter with a solid angle of delta omega = 0.62 sr, the A4 experiment is the first parity violation experiment to count individual scattering events. The measured asymmetry is A(phys)=(-5.44+/-0.54(stat)+/-0.26(sys))x10(-6). The standard model expectation assuming no strangeness contributions to the vector form factors is A(0) = (-6.30+/-0.43) x 10(-6). The difference is a direct measurement of the strangeness contribution to the vector form factors of the proton. The extracted value is G(s)(E) + 0.225G(s)(M) = 0.039+/-0.034 or F(s)(1) + 0.130F(s)(2) = 0.032+/-0.028.
Physical Review Letters 08/2004; 93(2):022002. · 7.37 Impact Factor
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G. Laveissière,
N. Degrande,
S. Jaminion,
C. Jutier,
L. Todor,
R. Di Salvo,
L. Van Hoorebeke,
L. C. Alexa,
B. D. Anderson,
K. A. Aniol, [......],
E. Voutier,
J. W. Watson,
L. B. Weinstein,
K. Wijesooriya,
R. Wilson,
B. B. Wojtsekhowski,
D. G. Zainea,
W-M. Zhang,
J. Zhao,
Z.-L. Zhou
[show abstract]
[hide abstract]
ABSTRACT: Exclusive electroproduction of π0 mesons on protons in the backward hemisphere has been studied at Q2=1.0 GeV2 by detecting protons in the forward direction in coincidence with scattered electrons from the 4 GeV electron beam in Jefferson Lab’s Hall A. The data span the range of the total (γ*p) center-of-mass energy W from the pion production threshold to W=2.0 GeV. The differential cross sections σT+ϵσL, σTL, and σTT were separated from the azimuthal distribution and are presented together with the MAID and SAID parametrizations.
Phys. Rev. C. 04/2004; 69(4).
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F. Kircher,
J. Fabre,
F. Gougnaud,
M. Humeau,
R. Leboeuf,
Y. Lussignol,
J. Marroncle,
G. Matichard, D. Marchand,
J.C. Sellier,
P. Vernin,
C. Veyssiere
[show abstract]
[hide abstract]
ABSTRACT: The determination of the beam energy in the experimental hall A of
TJNAF (previously CEBAF) accelerator is done through a very accurate
measurement of the field integral of a reference dipole magnet,
electrically connected in series with the bending magnets transporting
the beam from the accelerator to the experimental area. A new method is
used to determine the field integral; this method is described, as well
as the calibrations done in the laboratory. Finally, the goal to reach
an accuracy of the field integral on the order of 10<sup>-5</sup> has
been reached, as it is shown by comparing the results of the beam energy
determination obtained on the accelerator with this method to results
obtained by other independant methods
IEEE Transactions on Appiled Superconductivity 04/2000; · 1.04 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: The QED radiative corrections to virtual Compton scattering (reaction $e p \to e p \gamma$) are calculated to first order in $\alpha_{em} \equiv e^2 / 4 \pi$. A detailed study is presented for the one-loop virtual corrections and for the first order soft-photon emission contributions. Furthermore, a full numerical calculation is given for the radiative tail, corresponding with photon emission processes, where the photon energy is not very small compared with the lepton momenta. We compare our results with existing works on elastic electron-proton scattering, and show for the $e p \to e p \gamma$ reaction how the observables are modified due to these first order QED radiative corrections. We show results for both unpolarized and polarized observables of the virtual Compton scattering in the low energy region (where one is sensitive to the generalized polarizabilities of the nucleon), as well as for the deeply virtual Compton scattering. Comment: 74 pages, 19 figures
01/2000;
-
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.
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J ROCHE,
J M Friedrich,
D. Lhuillier,
P. Bartsch,
D. Baumann,
J Berthot,
P Y Bertin,
V. Breton,
W. U. Boeglin,
R. Bohm, [......],
G. Tamas,
M. Tytgat,
M. Vanderhaeghen,
L. Van Hoorebeke,
R. Van de Vyver,
J. Van de Wiele,
P. Vernin,
A Wagner,
Th. Walcher,
M Weiss
[show abstract]
[hide abstract]
ABSTRACT: Absolute differential cross sections for the reaction ep to ep gamma have been measured at a four-momentum transfer with virtuality Q/sup 2/=0.33 GeV/sup 2/ and polarization epsilon =0.62 in the range 33.6 to 111.5 MeV/c for the momentum of the outgoing photon in the photon-proton center of mass frame. The experiment has been performed with the high-resolution spectrometers at the Mainz Microtron MAMI. From the photon angular distributions, two structure functions which are a linear combination of the generalized polarizabilities have been determined for the first time.
-
J M Friedrich,
P. Bartsch,
D. Baumann,
J Berthot,
P Y Bertin,
V. Breton,
W. U. Boeglin,
R. Bohm,
N D'Hose,
T. Caprano, [......],
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: 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.
-
G. Laveissiere,
N. Degrande,
S. Jaminion,
C. Jutier,
L Todor,
R. Di Salvo,
L. Van Hoorebeke,
L.C. Alexa Stony,
B D Anderson,
K. A. Aniol, [......],
E. Voutier,
J. W. Watson,
L B Weinstein,
K. Wijesooriya,
R Wilson,
B. B. Wojtsekhowski,
D.G. Zainea,
W M Zhang,
J Zhao,
Z L Zhou
[show abstract]
[hide abstract]
ABSTRACT: Exclusive electroproduction of pi0 mesons on protons in the backward hemisphere has been studied at Q2=1.0 GeV2 by detecting protons in the forward direction in coincidence with scattered electrons from the 4 GeV electron beam in Jefferson Lab's Hall A. The data span the range of the total (gamma*p) center-of-mass energy W from the pion production threshold to W=2.0 GeV. The differential cross sections sigmaT+epsilonsigmaL, sigmaTL, and sigmaTT were separated from the azimuthal distribution and are presented together with the MAID and SAID parametrizations.
-
J. Roche,
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
[show abstract]
[hide abstract]
ABSTRACT: 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].
Nuclear Physics A.
-
M. Sudoł,
M. C. Mora Espí,
E. Becheva,
J. Boucher,
T. Hennino,
R. Kunne, D. Marchand,
S. Ong,
B. Ramstein,
J. Van de Wiele,
T. Zerguerras,
F. Maas,
B. Kopf,
M Pelizaeus,
M Steinke,
J Zhong,
E. Tomasi-Gustafsson
http://dx.doi.org/10.1140/epja/i2010-10960-8.
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