-
D. Wang,
K. Pan,
R. Subedi,
X. Deng,
Z. Ahmed,
K. Allada,
K. A. Aniol,
D. S. Armstrong,
J. Arrington,
V. Bellini, [......],
P. A. Souder,
R. Suleiman,
V. Sulkosky,
C. M. Sutera,
W. A. Tobias,
B. Waidyawansa,
B. Wojtsekhowski,
L. Ye,
B. Zhao,
X. Zheng
[show abstract]
[hide abstract]
ABSTRACT: We report on parity-violating asymmetries in the nucleon resonance region
measured using $5 - 6$ GeV longitudinally polarized electrons scattering off an
unpolarized deuterium target. These results are the first parity-violating
asymmetry data in the resonance region beyond the $\Delta(1232)$, and provide a
verification of quark-hadron duality in the nucleon electroweak $\gamma Z$
interference structure functions at the 10-15% level. The results are of
particular interest to models relevant for calculating the $\gamma Z$
box-diagram corrections to elastic parity-violating electron scattering
measurements.
04/2013;
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K. Ackerstaff,
A. Airapetian,
I. Akushevich,
N. Akopov,
M. Amarian,
E.C. Aschenauer,
R. Avakian,
H. Avakian,
A. Avetisian,
B. Bains, [......],
M.C. Vetterli,
E. Volk,
W. Wander,
T.P. Welch,
S.E. Williamson,
T. Wise,
T. Wolfel,
K. Zapfe-Duren,
G. Zograbian,
R. Zurmuhle
[show abstract]
[hide abstract]
ABSTRACT: Results are reported from the HERMES experiment at HERA on a measurement of the neutron spin structure function g1 n(x,Q 2) in deep inelastic scattering using 27.5 GeV longitudinally polarized positrons incident on a polarized 3He internal gas target. The data cover the kinematic range 0.023<x<0.6 and 1(GeV/c) 2<Q 2<15(GeV/c) 2. The integral ∫0.023 0.6g1 n(x)dx evaluated at a fixed Q 2 of 2.5(GeV/c) 2 is −0.034±0.013(stat.)±0.005(syst.). Assuming Regge behavior at low x, the first moment Γ1 n=∫0 1g1 n(x)dx is −0.037±0.013(stat.)±0.005(syst.)±0.006(extrapol.).
Physics Letters B 02/2013; 404(3-4):383-389. · 3.95 Impact Factor
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P. Monaghan,
R. Shneor,
R. Subedi,
B. D. Anderson,
K. Aniol,
J. Annand,
J. Arrington,
H. Benaoum,
F. Benmokhtar,
P. Bertin, [......],
G. M. Urciuoli,
E. Voutier,
K. Wang,
J. W. Watson,
L. B. Weinstein,
B. Wojtsekhowski,
S. Wood,
H. Yao,
X. Zheng,
L. Zhu
[show abstract]
[hide abstract]
ABSTRACT: The five-fold differential cross section for the 12C(e,e'p)11B reaction was
determined over a missing momentum range of 200-400 MeV/c, in a kinematics
regime with Bjorken x > 1 and Q2 = 2.0 (GeV/c)2. A comparison of the results
and theoretical models and previous lower missing momentum data is shown. The
theoretical calculations agree well with the data up to a missing momentum
value of 325 MeV/c and then diverge for larger missing momenta. The extracted
distorted momentum distribution is shown to be consistent with previous data
and extends the range of available data up to 400 MeV/c.
01/2013;
-
H. Fonvieille,
G. Laveissière,
N. Degrande,
S. Jaminion,
C. Jutier,
L. Todor,
R. Di Salvo,
L. Van Hoorebeke,
L. C. Alexa,
B. D. Anderson, [......],
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: Virtual Compton scattering (VCS) on the proton has been studied at the Jefferson Laboratory using the exclusive photon electroproduction reaction ep→epγ. This paper gives a detailed account of the analysis which has led to the determination of the structure functions PLL−PTT/ε and PLT and the electric and magnetic generalized polarizabilities (GPs) αE(Q2) and βM(Q2) at values of the four-momentum transfer squared Q2=0.92 and 1.76 GeV2. These data, together with the results of VCS experiments at lower momenta, help building a coherent picture of the electric and magnetic GPs of the proton over the full measured Q2 range and point to their nontrivial behavior.
Phys. Rev. C. 07/2012; 86(1).
-
Z Ahmed,
K Allada,
K A Aniol,
D S Armstrong,
J Arrington,
P Baturin,
V Bellini,
J Benesch,
R Beminiwattha,
F Benmokhtar, [......],
D Wang,
J Wexler,
R Wilson,
B Wojtsekhowski,
X Zhan,
X Yan,
H Yao,
L Ye,
B Zhao,
X Zheng
[show abstract]
[hide abstract]
ABSTRACT: The parity-violating cross-section asymmetry in the elastic scattering of polarized electrons from unpolarized protons has been measured at a four-momentum transfer squared Q2 = 0.624 GeV2 and beam energy E(b) = 3.48 GeV to be A(PV) = -23.80 ± 0.78(stat) ± 0.36(syst) parts per million. This result is consistent with zero contribution of strange quarks to the combination of electric and magnetic form factors G(E)(s) + 0.517G(M)(s) = 0.003 ± 0.010(stat) ± 0.004(syst) ± 0.009(ff), where the third error is due to the limits of precision on the electromagnetic form factors and radiative corrections. With this measurement, the world data on strange contributions to nucleon form factors are seen to be consistent with zero and not more than a few percent of the proton form factors.
Physical Review Letters 03/2012; 108(10):102001. · 7.37 Impact Factor
-
J Huang,
K Allada,
C Dutta,
J Katich,
X Qian,
Y Wang,
Y Zhang,
K Aniol,
J R M Annand,
T Averett, [......],
Y Ye,
Z Ye,
L Yuan,
X Zhan,
Y-W Zhang,
B Zhao,
X Zheng,
L Zhu,
X Zhu,
X Zong
[show abstract]
[hide abstract]
ABSTRACT: We report the first measurement of the double-spin asymmetry A{LT} for charged pion electroproduction in semi-inclusive deep-inelastic electron scattering on a transversely polarized {3}He target. The kinematics focused on the valence quark region, 0.16<x<0.35 with 1.4<Q{2}<2.7 GeV{2}. The corresponding neutron A{LT} asymmetries were extracted from the measured {3}He asymmetries and proton over {3}He cross section ratios using the effective polarization approximation. These new data probe the transverse momentum dependent parton distribution function g{1T}{q} and therefore provide access to quark spin-orbit correlations. Our results indicate a positive azimuthal asymmetry for π{-} production on {3}He and the neutron, while our π{+} asymmetries are consistent with zero.
Physical Review Letters 02/2012; 108(5):052001. · 7.37 Impact Factor
-
M. Mihovilovic,
K. Allada,
B. D. Anderson,
J. R. M. Annand,
T. Averett,
A. Camsonne,
R. W. Chan,
J. -P. Chen,
K. Chirapatpimol, C. W. de Jager, [......],
G. Rosner,
B. Sawatzky,
M. Shabestari,
A. Shahinyan,
R. Shneor,
S. Sirca,
R. Subedi,
V. Sulkosky,
J. W. Watson,
Y. -W. Zhang
[show abstract]
[hide abstract]
ABSTRACT: The techniques for optical calibration of Jefferson Lab's large-acceptance
magnetic hadron spectrometer, BigBite, have been examined. The most consistent
and stable results were obtained by using a method based on singular value
decomposition. In spite of the complexity of the optics, the particles'
positions and momenta at the target have been precisely reconstructed from the
coordinates measured in the detectors by means of a single back-tracing matrix.
The technique is applicable to any similar magnetic spectrometer and any
particle type. For 0.55 GeV/c protons, we have established the vertex
resolution of 1.2 cm, angular resolutions of 7 mrad and 16 mrad (in-plane and
out-of-plane, respectively), and a relative momentum resolution of 1.6%.
01/2012;
-
W U Boeglin,
L Coman,
P Ambrozewicz,
K Aniol,
J Arrington,
G Batigne,
P Bosted,
A Camsonne,
G Chang,
J P Chen, [......],
M Roedelbronn,
A Saha,
K Slifer,
P Solvignon,
V Sulkosky,
P E Ulmer,
E Voutier,
L B Weinstein,
B Wojtsekhowski,
M Zeier
[show abstract]
[hide abstract]
ABSTRACT: The (2)H(e,e'p)n cross section at a momentum transfer of 3.5 (GeV/c)(2) was measured over a kinematical range that made it possible to study this reaction for a set of fixed missing momenta as a function of the neutron recoil angle θ(nq) and to extract missing momentum distributions for fixed values of θ(nq) up to 0.55 GeV/c. In the region of 35°≤θ(nq)≤45° recent calculations, which predict that final-state interactions are small, agree reasonably well with the experimental data. Therefore, these experimental reduced cross sections provide direct access to the high momentum component of the deuteron momentum distribution in exclusive deuteron electrodisintegration.
Physical Review Letters 12/2011; 107(26):262501. · 7.37 Impact Factor
-
S Abrahamyan,
Z Ahmed,
K Allada,
D Anez,
T Averett,
A Barbieri,
K Bartlett,
J Beacham,
J Bono,
J R Boyce, [......],
J Segal,
L Selvy,
A Shahinyan,
R Subedi,
V Sulkosky,
S Stepanyan,
N Toro,
D Walz,
B Wojtsekhowski,
J Zhang
[show abstract]
[hide abstract]
ABSTRACT: We present a search at the Jefferson Laboratory for new forces mediated by sub-GeV vector bosons with weak coupling α' to electrons. Such a particle A' can be produced in electron-nucleus fixed-target scattering and then decay to an e + e- pair, producing a narrow resonance in the QED trident spectrum. Using APEX test run data, we searched in the mass range 175-250 MeV, found no evidence for an A'→ e+ e- reaction, and set an upper limit of α'/α ~/= 10(-6). Our findings demonstrate that fixed-target searches can explore a new, wide, and important range of masses and couplings for sub-GeV forces.
Physical Review Letters 11/2011; 107(19):191804. · 7.37 Impact Factor
-
X Qian,
K Allada,
C Dutta,
J Huang,
J Katich,
Y Wang,
Y Zhang,
K Aniol,
J R M Annand,
T Averett, [......],
H F Ibrahim,
M Iodice,
X Jiang,
G Jin,
M K Jones,
A Kelleher,
W Kim,
A Kolarkar,
W Korsch,
J J Lerose
09/2011; 11(6):11-14.
-
X Qian,
K Allada,
C Dutta,
J Huang,
J Katich,
Y Wang,
Y Zhang,
K Aniol,
J R M Annand,
T Averett, [......],
Y Ye,
Z Ye,
L Yuan,
X Zhan,
Y-W Zhang,
B Zhao,
X Zheng,
L Zhu,
X Zhu,
X Zong
[show abstract]
[hide abstract]
ABSTRACT: We report the first measurement of target single spin asymmetries in the semi-inclusive (3)He(e,e'π(±))X reaction on a transversely polarized target. The experiment, conducted at Jefferson Lab using a 5.9 GeV electron beam, covers a range of 0.16 < x < 0.35 with 1.4 < Q(2) < 2.7 GeV(2). The Collins and Sivers moments were extracted from the azimuthal angular dependence of the measured asymmetries. The π(±) Collins moments for (3)He are consistent with zero, except for the π(+) moment at x = 0.35, which deviates from zero by 2.3σ. While the π(-) Sivers moments are consistent with zero, the π(+) Sivers moments favor negative values. The neutron results were extracted using the nucleon effective polarization and measured cross section ratios of proton to (3)He, and are largely consistent with the predictions of phenomenological fits and quark model calculations.
Physical Review Letters 08/2011; 107(7):072003. · 7.37 Impact Factor
-
J. Huang,
K. Allada,
C. Dutta,
J. Katich,
X. Qian,
Y. Wang,
Y. Zhang,
K. Aniol,
J. R. M. Annand,
T. Averett, [......],
Z. Ye,
L. Yuan,
X. Zhan,
Y. -W. Zhang,
B. Zhao,
X. Zheng,
L. Zhu,
X. Zhu,
X. Zong,
for the Jefferson Lab Hall A Collaboration
[show abstract]
[hide abstract]
ABSTRACT: We report the first measurement of the double-spin asymmetry $A_{LT}$ for
charged pion electroproduction in semi\nobreakdash-inclusive
deep\nobreakdash-inelastic electron scattering on a transversely polarized
$^{3}$He target. The kinematics focused on the valence quark region,
$0.16<x<0.35$ with $1.4<Q^{2}<2.7\,\textrm{GeV}^{2}$. The corresponding neutron
$A_{LT}$ asymmetries were extracted from the measured $^{3}$He asymmetries and
proton over $^{3}$He cross section ratios using the effective polarization
approximation. These new data probe the transverse momentum dependent parton
distribution function $g_{1T}^{q}$ and therefore provide access to quark
spin-orbit correlations. Our results indicate a positive azimuthal asymmetry
for $\pi^{-}$ production on $^{3}$He and the neutron, while our $\pi^{+}$
asymmetries are consistent with zero.
08/2011;
-
HAPPEX collaboration,
Z. Ahmed,
K. Allada,
K. A. Aniol,
D. S. Armstrong,
J. Arrington,
P. Baturin,
V. Bellini,
J. Benesch,
R. Beminiwattha, [......],
D Wang,
J. Wexler,
R Wilson,
B Wojtsekhowski,
X Zhan,
X Yan,
H Yao,
L. Ye,
B Zhao,
X Zheng
[show abstract]
[hide abstract]
ABSTRACT: The parity-violating cross-section asymmetry in the elastic scattering of
polarized electrons from unpolarized protons has been measured at a
four-momentum transfer squared Q2 = 0.624 GeV and beam energy E =3.48 GeV to be
A_PV = -23.80 +/- 0.78 (stat) +/- 0.36 (syst) parts per million. This result is
consistent with zero contribution of strange quarks to the combination of
electric and magnetic form factors G_E^s + 0.517 G_M^s = 0.003 +/- 0.010 (stat)
+/- 0.004 (syst) +/- 0.009 (ff), where the third error is due to the limits of
precision on the electromagnetic form factors and radiative corrections. With
this measurement, the world data on strange contributions to nucleon form
factors are seen to be consistent with zero and not more than a few percent of
the proton form factors.
07/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: The u- and d-quark contributions to the elastic nucleon electromagnetic form factors have been determined by using experimental data on G(E)(n), G(M)(n), G(E)(p), and G(M)(p). Such a flavor separation of the form factors became possible up to negative four-momentum transfer squared Q(2) = 3.4 GeV(2) with recent data on G(E)(n) from Hall A at Jefferson Lab. For Q(2) above 1 GeV(2), for both the u and the d quark, the ratio of the Pauli and Dirac form factors, F(2)/F(1), was found to be almost constant in sharp contrast to the behavior of F(2)/F(1) for the proton as a whole. Also, again for Q(2)>1 GeV(2), both F(2)(d) and F(1)(d) are roughly proportional to 1/Q(4), whereas the dropoff of F(2)(u) and F(1)(u) is more gradual.
Physical Review Letters 06/2011; 106(25):252003. · 7.37 Impact Factor
-
X Qian,
K. Allada,
C. Dutta,
J Huang,
J. Katich,
Y Wang,
Y Zhang,
K. Aniol,
J. R. M. Annand,
T. Averett, [......],
Y Ye,
Z Ye,
L Yuan,
X Zhan,
Y W Zhang,
B Zhao,
X Zheng,
L Zhu,
X Zhu,
X Zong
[show abstract]
[hide abstract]
ABSTRACT: We report the first measurement of target single spin asymmetries in the
semi-inclusive $^3{He}(e,e'\pi^\pm)X$ reaction on a transversely polarized
target. The experiment, conducted at Jefferson Lab using a 5.9 GeV electron
beam, covers a range of 0.14 $< x <$ 0.34 with 1.3 $<Q^2<$ 2.7 GeV$^2$. The
Collins and Sivers moments were extracted from the azimuthal angular dependence
of the measured asymmetries. The extracted $\pi^\pm$ Collins moments for $^3$He
are consistent with zero, except for the $\pi^+$ moment at $x=0.34$, which
deviates from zero by 2.3$\sigma$. While the $\pi^-$ Sivers moments are
consistent with zero, the $\pi^+$ Sivers moments favor negative values. The
neutron results were extracted using the nucleon effective polarization and the
measured cross section ratio of proton to $^3$He, and are largely consistent
with the predictions of phenomenological fits and quark model calculations.
06/2011;
-
G. Ron,
X Zhan,
J. Glister,
B Lee,
K. Allada,
W. Armstrong,
J. Arrington,
A Beck,
F. Benmokhtar,
B L Berman, [......],
J Song,
R. Sparks,
R. Subedi,
S Strauch,
G. M. Urciuoli,
K Wang,
B Wojtsekhowski,
X Yan,
H Yao,
X Zhu
[show abstract]
[hide abstract]
ABSTRACT: We present an updated extraction of the proton electromagnetic form factor
ratio, mu_p G_E/G_M, at low Q^2. The form factors are sensitive to the spatial
distribution of the proton, and precise measurements can be used to constrain
models of the proton. An improved selection of the elastic events and reduced
background contributions yielded a small systematic reduction in the ratio mu_p
G_E/G_M compared to the original analysis.
03/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: The u- and d-quark contributions to the elastic nucleon electromagnetic form
factors have been determined using experimental data on GEn, GMn, GpE, and GpM.
Such a flavor separation of the form factors became possible up to 3.4 GeV2
with recent data on GEn from Hall A at JLab. At a negative four-momentum
transfer squared Q2 above 1 GeV2, for both the u- and d-quark components, the
ratio of the Pauli form factor to the Dirac form factor, F2/F1, was found to be
almost constant, and for each of F2 and F1 individually, the d-quark portions
of both form factors drop continuously with increasing Q2.
03/2011;
-
A. J. R. Puckett,
E. J. Brash,
O. Gayou,
M. K. Jones,
L. Pentchev,
C. F. Perdrisat,
V. Punjabi,
K. A. Aniol,
T. Averett,
F. Benmokhtar, [......],
I. Sitnik,
S. Strauch,
L. Todor,
E. Tomasi-Gustafsson,
G. M. Urciuoli,
H. Voskanyan,
K. Wijesooriya,
B. B. Wojtsekhowski,
X. Zheng,
L. Zhu
[show abstract]
[hide abstract]
ABSTRACT: Precise measurements of the proton electromagnetic form factor ratio $R =
\mu_p G_E^p/G_M^p$ using the polarization transfer method at Jefferson Lab have
revolutionized the understanding of nucleon structure by revealing the strong
decrease of $R$ with momentum transfer $Q^2$ for $Q^2 \gtrsim 1$ GeV$^2$, in
strong disagreement with previous extractions of $R$ from cross section
measurements. In particular, the polarization transfer results have exposed the
limits of applicability of the one-photon-exchange approximation and
highlighted the role of quark orbital angular momentum in the nucleon
structure. The GEp-II experiment in Jefferson Lab's Hall A measured $R$ at four
$Q^2$ values in the range 3.5 GeV$^2 \le Q^2 \le 5.6$ GeV$^2$. A possible
discrepancy between the originally published GEp-II results and more recent
measurements at higher $Q^2$ motivated a new analysis of the GEp-II data. This
article presents the final results of the GEp-II experiment, including details
of the new analysis, an expanded description of the apparatus and an overview
of theoretical progress since the original publication. The key result of the
final analysis is a systematic increase in the results for $R$, improving the
consistency of the polarization transfer data in the high-$Q^2$ region. This
increase is the result of an improved selection of elastic events which largely
removes the systematic effect of the inelastic contamination, underestimated by
the original analysis.
02/2011;
-
S P Malace,
M Paolone,
S Strauch,
I Albayrak,
J Arrington,
B L Berman,
E J Brash,
B Briscoe,
A Camsonne,
J-P Chen, [......],
R R Subedi,
L Tang,
D Tedeschi,
V Tvaskis,
J M Udias,
P E Ulmer,
J R Vignote,
F R Wesselmann,
B Wojtsekhowski,
X Zhan
[show abstract]
[hide abstract]
ABSTRACT: We measured with unprecedented precision the induced polarization P(y) in (4)He(e,e'p)(3)H at Q(2)=0.8 and 1.3 (GeV/c)(2). The induced polarization is indicative of reaction-mechanism effects beyond the impulse approximation. Our results are in agreement with a relativistic distorted-wave impulse approximation calculation but are overestimated by a calculation with strong charge-exchange effects. Our data are used to constrain the strength of the spin-independent charge-exchange term in the latter calculation.
Physical Review Letters 02/2011; 106(5):052501. · 7.37 Impact Factor
-
X. Zhan,
K. Allada,
D. S. Armstrong,
J. Arrington,
W. Bertozzi,
W. Boeglin,
J. -P. Chen,
K. Chirapatpimol,
S. Choi,
E. Chudakov, [......],
P. Solvignon,
N. F. Sparveris,
S. Strauch,
R. Subedi,
V. Sulkosky,
I. Vilardi,
Y. Wang,
B. Wojtsekhowski,
Z. Ye,
Y. Zhang
[show abstract]
[hide abstract]
ABSTRACT: We report a new, high-precision measurement of the proton elastic form factor
ratio \mu_p G_E/G_M for the four-momentum transfer squared Q^2 = 0.3-0.7
(GeV/c)^2. The measurement was performed at Jefferson Lab (JLab) in Hall A
using recoil polarimetry. With a total uncertainty of approximately 1%, the new
data clearly show that the deviation of the ratio \mu_p G_E/G_M from unity
observed in previous polarization measurements at high Q^2 continues down to
the lowest Q^2 value of this measurement. The updated global fit that includes
the new results yields an electric (magnetic) form factor roughly 2% smaller
(1% larger) than the previous global fit in this Q^2 range. We obtain new
extractions of the proton electric and magnetic radii, which are
<r^2_E>^(1/2)=0.875+/-0.010 fm and <r^2_M>^(1/2)=0.867+/-0.020 fm. The charge
radius is consistent with other recent extractions based on the electron-proton
interaction, including the atomic hydrogen Lamb shift measurements, which
suggests a missing correction in the comparison of measurements of the proton
charge radius using electron probes and the recent extraction from the muonic
hydrogen Lamb shift.
02/2011;
