-
Collaboration,
D. Androic,
D. S. Armstrong,
J. Arvieux,
S. L. Bailey,
D. H. Beck,
E. J. Beise,
J. Benesch,
F. Benmokhtar,
L. Bimbot, [......],
M. Stutzman,
R. Suleiman,
V. Tadevosyan,
W. T. H. van Oers,
M. Versteegen,
E. Voutier,
W. Vulcan, S. P. Wells,
S. E. Williamson,
S. A. Wood
[show abstract]
[hide abstract]
ABSTRACT: The parity-violating asymmetry arising from inelastic electron-nucleon
scattering at backward angle (~95 degrees) near the Delta(1232) resonance has
been measured using a hydrogen target. From this asymmetry, we extracted the
axial transition form factor G^A_{N\Delta}, a function of the axial Adler form
factors C^A_i. Though G^A_{N\Delta} has been previously studied using charged
current reactions, this is the first measurement of the weak neutral current
excitation of the Delta using a proton target. For Q^2 = 0.34 (GeV/c)^2 and W =
1.18 GeV, the asymmetry was measured to be -33.4 \pm (5.3)_{stat} \pm
(5.1)_{sys} ppm. The value of G^A_{N\Delta} determined from the hydrogen
asymmetry was -0.05 \pm (0.35)_{stat} \pm (0.34)_{sys} \pm (0.06)_{theory}.
These findings agree within errors with theoretical predictions for both the
total asymmetry and the form factor. In addition to the hydrogen measurement,
the asymmetry was measured at the same kinematics using a deuterium target. The
asymmetry for deuterium was determined to be -43.6 \pm (14.6)_{stat} \pm
(6.2)_{sys} ppm.
12/2012;
-
D Androić,
D S Armstrong,
J Arvieux,
S L Bailey,
D H Beck,
E J Beise,
J Benesch,
F Benmokhtar,
L Bimbot,
J Birchall, [......],
M Stutzman,
R Suleiman,
V Tadevosyan,
W T H van Oers,
M Versteegen,
E Voutier,
W Vulcan, S P Wells,
S E Williamson,
S A Wood
[show abstract]
[hide abstract]
ABSTRACT: The parity-violating (PV) asymmetry of inclusive π- production in electron scattering from a liquid deuterium target was measured at backward angles. The measurement was conducted as a part of the G0 experiment, at a beam energy of 360 MeV. The physics process dominating pion production for these kinematics is quasifree photoproduction off the neutron via the Δ0 resonance. In the context of heavy-baryon chiral perturbation theory, this asymmetry is related to a low-energy constant d(Δ)- that characterizes the parity-violating γNΔ coupling. Zhu et al. calculated d(Δ)- in a model benchmarked by the large asymmetries seen in hyperon weak radiative decays, and predicted potentially large asymmetries for this process, ranging from A(γ)-=-5.2 to +5.2 ppm. The measurement performed in this work leads to A(γ)-=-0.36±1.06±0.37±0.03 ppm (where sources of statistical, systematic and theoretical uncertainties are included), which would disfavor enchancements considered by Zhu et al. proportional to V(ud)/V(us). The measurement is part of a program of inelastic scattering measurements that were conducted by the G0 experiment, seeking to determine the N-Δ axial transition form factors using PV electron scattering.
Physical Review Letters 03/2012; 108(12):122002. · 7.37 Impact Factor
-
D Androić,
D S Armstrong,
J Arvieux,
S L Bailey,
D H Beck,
E J Beise,
J Benesch,
F Benmokhtar,
L Bimbot,
J Birchall, [......],
V Tadevosyan,
W T H van Oers,
M Versteegen,
E Voutier,
W Vulcan, S P Wells,
S E Williamson,
S A Wood,
B Pasquini,
M Vanderhaeghen
[show abstract]
[hide abstract]
ABSTRACT: We have measured the beam-normal single-spin asymmetries in elastic scattering of transversely polarized electrons from the proton, and performed the first measurement in quasielastic scattering on the deuteron, at backward angles (lab scattering angle of 108°) for Q² = 0.22 GeV²/c² and 0.63 GeV²/c² at beam energies of 362 and 687 MeV, respectively. The asymmetry arises due to the imaginary part of the interference of the two-photon exchange amplitude with that of single-photon exchange. Results for the proton are consistent with a model calculation which includes inelastic intermediate hadronic (πN) states. An estimate of the beam-normal single-spin asymmetry for the scattering from the neutron is made using a quasistatic deuterium approximation, and is also in agreement with theory.
Physical Review Letters 07/2011; 107(2):022501. · 7.37 Impact Factor
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The Collaboration,
D. Androić,
D. S. Armstrong,
J. Arvieux,
S L Bailey,
D. H. Beck,
E. J. Beise,
J. Benesch,
F. Benmokhtar,
L. Bimbot, [......],
V. Tadevosyan,
W T H Van Oers,
M. Versteegen,
E. Voutier,
W. Vulcan, S.P. Wells,
S. E. Williamson,
S. A. Wood,
B. Pasquini,
M. Vanderhaeghen
[show abstract]
[hide abstract]
ABSTRACT: We have measured the beam-normal single-spin asymmetries in elastic
scattering of transversely polarized electrons from the proton, and performed
the first measurement in quasi-elastic scattering on the deuteron, at backward
angles (lab scattering angle of 108 degrees) for Q2 = 0.22 GeV^2/c^2 and 0.63
GeV^2/c^2 at beam energies of 362 MeV and 687 MeV, respectively. The asymmetry
arises due to the imaginary part of the interference of the two-photon exchange
amplitude with that of single photon exchange. Results for the proton are
consistent with a model calculation which includes inelastic intermediate
hadronic (piN) states. An estimate of the beam-normal single-spin asymmetry for
the scattering from the neutron is made using a quasi-static deuterium
approximation, and is also in agreement with theory.
03/2011;
-
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;
-
D Androić,
D S Armstrong,
J Arvieux,
S L Bailey,
D H Beck,
E J Beise,
J Benesch,
F Benmokhtar,
L Bimbot,
J Birchall, [......],
M Stutzman,
R Suleiman,
V Tadevosyan,
W T H van Oers,
M Versteegen,
E Voutier,
W Vulcan, S P Wells,
S E Williamson,
S A Wood
[show abstract]
[hide abstract]
ABSTRACT: We have measured parity-violating asymmetries in elastic electron-proton and quasielastic electron-deuteron scattering at Q2=0.22 and 0.63 GeV2. They are sensitive to strange quark contributions to currents in the nucleon and the nucleon axial-vector current. The results indicate strange quark contributions of approximately < 10% of the charge and magnetic nucleon form factors at these four-momentum transfers. We also present the first measurement of anapole moment effects in the axial-vector current at these four-momentum transfers.
Physical Review Letters 01/2010; 104(1):012001. · 7.37 Impact Factor
-
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
-
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
-
T M Ito,
T Averett,
D Barkhuff,
G Batigne,
D H Beck,
E J Beise,
A Blake,
H Breuer,
R Carr,
B Clasie, [......],
R Suleiman,
S Taylor,
R Tieulent,
B Tipton,
E Tsentalovich, S P Wells,
B Yang,
J Yuan,
J Yun,
T Zwart
[show abstract]
[hide abstract]
ABSTRACT: We report on a new measurement of the parity-violating asymmetry in quasielastic electron scattering from the deuteron at backward angles at Q2=0.038 (GeV/c)2. This quantity provides a determination of the neutral weak axial vector form factor of the nucleon, which can potentially receive large electroweak corrections. The measured asymmetry A=-3.51+/-0.57 (stat)+/-0.58 (syst) ppm is consistent with theoretical predictions. We also report on updated results of the previous experiment at Q2=0.091 (GeV/c)2, which are also consistent with theoretical predictions.
Physical Review Letters 04/2004; 92(10):102003. · 7.37 Impact Factor
-
R. Hasty,
A. M. Hawthorne-Allen,
T. Averett,
D. Barkhuff,
D. H. Beck,
E. J. Beise,
A. Blake,
H. Breuer,
R. Carr,
S. Covrig, [......],
M. Pitt,
J. Ritter,
J. Roche,
V. Savu,
D. T. Spayde,
R. Tieulent,
E. Tsentalovich, S. P. Wells,
B. Yang,
T. Zwart
[show abstract]
[hide abstract]
ABSTRACT: The violation of mirror symmetry in the weak force provides a powerful tool to study the internal structure of the proton.
Experimental results have been obtained that address the role of strange quarks in generating nuclear magnetism. The measurement
reported here provides an unambiguous constraint on strange quark contributions to the proton's magnetic moment through the
electron-proton weak interaction. We also report evidence for the existence of a parity-violating electromagnetic effect known
as the anapole moment of the proton. The proton's anapole moment is not yet well understood theoretically, but it could have
important implications for precision weak interaction studies in atomic systems such as cesium.
Science 12/2000; 290(5499):2117-2119. · 31.20 Impact Factor
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S.P. Wells,
T. Averett,
D Barkhuff,
D. H. Beck,
E. J. Beise,
C. Benson,
H. Breuer,
R Carr,
S Covrig,
J. DelCorso, [......],
P. Naik,
M. L. Pitt,
J Ritter,
V Savu,
D. T. Spayde,
M Sullivan,
R. Tieulent,
E. Tsentalovich,
B Yang,
T. Zwart
[show abstract]
[hide abstract]
ABSTRACT: We report the first measurement of the vector analyzing power in inclusive
transversely polarized elastic electron-proton scattering at Q^2 = 0.1
(GeV/c)^2 and large scattering angles. This quantity should vanish in the
single virtual photon exchange, plane wave impulse approximation for this
reaction, and can therefore provide information on double photon exchange
amplitudes for electromagnetic interactions with hadronic systems. We find a
non-zero value of A=-15.4+/-5.4 ppm. No calculations of this observable for
nuclei other than spin 0 have been carried out in these kinematics, and the
calculation using the spin orbit interaction from a charged point nucleus of
spin 0 cannot describe these data.
02/2000;
-
D. H. Barkhuff, S.P. Wells,
T. Averett,
D. H. Beck,
E. J. Beise,
D. Cheever,
G. Dodson,
S. Kowalski,
R. D. McKeown,
B. A. Mueller,
M. Pitt,
D. Spayde,
C. Tschalaer,
A. Zolfaghari
[show abstract]
[hide abstract]
ABSTRACT: We report the development and implementation of an energy feedback system for the MIT/Bates Linear Accelerator Center. General requirements of the system are described, as are the specific requirements, features, and components of the system unique to its implementation at the Bates Laboratory. We demonstrate that with the system in operation, energy fluctuations correlated with the 60 Hz line voltage and with drifts of thermal origin are reduced by an order of magnitude.
11/1999;
-
B Mueller,
D. H. Beck,
E. J. Beise,
E. Candell,
L. Cardman,
R Carr,
R. C. DiBari,
G. Dodson,
K. Dow,
F. Duncan, [......],
S. Kowalski,
A. Lung,
R. D. McKeown,
R. Mohring,
J. Napolitano,
D. Nilsson,
M. Pitt,
N. Simicevic,
B. Terburg, S.P. Wells
[show abstract]
[hide abstract]
ABSTRACT: We report the first measurement of the parity-violating asymmetry in elastic electron scattering from the proton. The asymmetry depends on the neutral weak magnetic form factor of the proton which contains new information on the contribution of strange quark-antiquark pairs to the magnetic moment of the proton. We obtain the value $G_M^Z= 0.34 \pm 0.09 \pm 0.04 \pm 0.05$ n.m. at $Q^2=0.1$ (GeV/c)${}^2$. Comment: 4 pages TEX, text available at http://www.krl.caltech.edu/preprints/OAP.html
02/1997;
-
S.P. Wells,
T. Averett,
D Barkhuff,
D. H. Beck,
E. J. Beise,
C. Benson,
H. Breuer,
R Carr,
S Covrig,
J. DelCorso, [......],
P. Naik,
M. L. Pitt,
J Ritter,
V Savu,
D. T. Spayde,
M Sullivan,
R. Tieulent,
E. Tsentalovich,
B Yang,
T. Zwart
[show abstract]
[hide abstract]
ABSTRACT: We report the first measurement of the vector analyzing power in inclusive transversely polarized elastic electron- proton scattering at Q(2) = 0.1 (GeV/c)(2) and large scattering angles. This quantity must vanish in the single virtual photon exchange, plane-wave impulse approximation for this reaction, and can therefore provide information on two photon exchange amplitudes for electromagnetic interactions with hadronic systems. The observable we have measured is driven by the imaginary part of the two photon exchange amplitude, the hadronic side of which is simply the Compton amplitude for the proton with two virtual photons. We find a small but nonzero value of A = -15.4 +/- 5.4 ppm.
-
J. S. Real,
D. Androic,
D. S. Armstrong,
J. Arvieux,
S L Bailey,
D. H. Beck,
E. J. Beise,
J. Benesch,
F. Benmokhtar,
L. Bimbot, [......],
D. T. Spayde,
M. Stutzman,
R Suleiman,
V. Tadevosyan,
M. Versteegen,
E. Voutier,
W. Vulcan, S.P. Wells,
S. E. Williamson,
S. A. Wood
EPJ Web of Conferences.
-
J. S. Real,
D. Androić,
D. S. Armstrong,
J. Arvieux,
S L Bailey,
D. H. Beck,
E. J. Beise,
J. Benesch,
F. Benmokhtar,
L. Bimbot, [......],
D. T. Spayde,
M. Stutzman,
R Suleiman,
V. Tadevosyan,
M. Versteegen,
E. Voutier,
W. Vulcan, S.P. Wells,
S. E. Williamson,
S. A. Wood
http://dx.doi.org/10.1051/epjconf/20100303004.
-
G. MacLachlan,
A. Aghalaryan,
A. Ahmidouch,
B.D. Anderson,
R. Asaturyan,
O. Baker,
A.R. Baldwin,
D. Barkhuff,
H. Breuer,
R. Carlini, [......], S.P. Wells,
F. Wesselmann,
S. Wood,
C. Yan,
Chenyu Yan,
S. Yang,
L. Yuan,
W.-M. Zhang,
H. Zhu,
X. Zhu
[show abstract]
[hide abstract]
ABSTRACT: Recoil polarimetry was used to extract the ratio of the proton electromagnetic form factors, , at Q2=1.13 2(GeV/c) from the reaction . This was an ancillary measurement in which the proton polarization was determined as part of a larger program utilizing a stand-alone polarimeter designed to measure . This measurement complements previous recoil polarimetry measurements of made at the Thomas Jefferson National Accelerator Facility.
Nuclear Physics A. 764:261-273.
