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J Lachniet,
A Afanasev,
H Arenhövel,
W K Brooks,
G P Gilfoyle,
D Higinbotham,
S Jeschonnek,
B Quinn,
M F Vineyard,
G Adams, [......],
M Williams,
E Wolin,
M H Wood,
A Yegneswaran,
J Yun,
M Yurov,
L Zana,
J Zhang,
B Zhao,
Z W Zhao
[show abstract]
[hide abstract]
ABSTRACT: The neutron elastic magnetic form factor was extracted from quasielastic electron scattering on deuterium over the range Q;{2}=1.0-4.8 GeV2 with the CLAS detector at Jefferson Lab. High precision was achieved with a ratio technique and a simultaneous in situ calibration of the neutron detection efficiency. Neutrons were detected with electromagnetic calorimeters and time-of-flight scintillators at two beam energies. The dipole parametrization gives a good description of the data.
Physical Review Letters 06/2009; 102(19):192001. · 7.37 Impact Factor
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M Nozar,
C Salgado,
D P Weygand,
L Guo,
G Adams,
Ji Li,
P Eugenio,
M J Amaryan,
M Anghinolfi,
G Asryan, [......],
D P Watts,
L B Weinstein,
M Williams,
E Wolin,
M H Wood,
A Yegneswaran,
L Zana,
J Zhang,
B Zhao,
Z W Zhao
[show abstract]
[hide abstract]
ABSTRACT: A search for exotic mesons in the pi;{+}pi;{+}pi;{-} system photoproduced by the charge exchange reaction gammap-->pi;{+}pi;{+}pi;{-}(n) was carried out by the CLAS Collaboration at Jefferson Lab. A tagged-photon beam with energies in the 4.8 to 5.4 GeV range, produced through bremsstrahlung from a 5.744 GeV electron beam, was incident on a liquid-hydrogen target. A partial wave analysis was performed on a sample of 83 000 events, the highest such statistics to date in this reaction at these energies. The main objective of this study was to look for the photoproduction of an exotic J;{PC}=1;{-+} resonant state in the 1 to 2 GeV mass range. Our partial wave analysis shows production of the a_{2}(1320) and the pi_{2}(1670) mesons, but no evidence for the a_{1}(1260), nor the pi_{1}(1600) exotic state at the expected levels. An upper limit of 13.5 nb is determined for the exotic pi_{1}(1600) cross section, less than 2% of the a_{2}(1320) production.
Physical Review Letters 04/2009; 102(10):102002. · 7.37 Impact Factor
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The CLAS Collaboration,
S. A. Morrow,
M. Guidal,
M. Garçon,
J. M. Laget,
E. S. Smith,
G. Adams,
K. P. Adhikari,
M. Aghasyan,
M. J. Amaryan, [......],
D. P. Weygand,
M. Williams,
E. Wolin,
M. H. Wood,
A. Yegneswaran,
M. Yurov,
L. Zana,
J. Zhang,
B. Zhao,
Z. W. Zhao
[show abstract]
[hide abstract]
ABSTRACT: The ep → e
′
pρ0 reaction has been measured using the 5.754GeV electron beam of Jefferson Lab and the CLAS detector. This represents the largest
ever set of data for this reaction in the valence region. Integrated and differential cross-sections are presented. The W , Q2 and t dependences of the cross-section are compared to theoretical calculations based on the t -channel meson-exchange Regge theory, on the one hand, and on quark handbag diagrams related to Generalized Parton Distributions
(GPDs) on the other hand. The Regge approach can describe at the » \approx 30% level most of the features of the present data while the two GPD calculations that are presented in this article which
succesfully reproduce the high-energy data strongly underestimate the present data. The question is then raised whether this
discrepancy originates from an incomplete or inexact way of modelling the GPDs or the associated hard scattering amplitude
or whether the GPD formalism is simply inapplicable in this region due to higher-twists contributions, incalculable at present.
European Physical Journal A 12/2008; 39(1):5-31. · 2.19 Impact Factor
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R. Nasseripour,
B. A. Raue,
D. S. Carman,
P. Ambrozewicz,
M. J. Amaryan,
E. Anciant,
M. Anghinolfi,
B. Asavapibhop,
G. Asryan,
G. Audit, [......],
D. P. Weygand,
M. Williams,
E. Wolin,
M. H. Wood,
A. Yegneswaran,
J. Yun,
L. Zana,
J. Zhang,
B. Zhao,
Z. W. Zhao
[show abstract]
[hide abstract]
ABSTRACT: The first measurements of the polarized structure function σLT' for the reaction 1H(e⃗,e'K+)Λ in the nucleon resonance region are reported. Measurements are included from threshold up to W=2.05 GeV for central values of Q2 of 0.65 and 1.00 GeV2, and nearly the entire kaon center-of-mass angular range. σLT' is the imaginary part of the longitudinal-transverse response and is expected to be sensitive to interferences between competing intermediate s-channel resonances, as well as resonant and nonresonant processes. The results for σLT' are comparable in magnitude to previously reported results from CLAS for σLT, the real part of the same response. An intriguing sign change in σLT' is observed in the high Q2 data at W≈1.9 GeV. Comparisons to several existing model predictions are shown.
Phys. Rev. C. 06/2008; 77(6).
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K. Park,
V. D. Burkert,
W. Kim,
I. G. Aznauryan,
R. Minehart,
L. C. Smith,
K. Joo,
L. Elouadrhiri,
G. Adams,
M. J. Amaryan, [......],
E. Wolin,
M. H. Wood,
A. Yegneswaran,
J. Yun,
M. Yurov,
L. Zana,
B. Zhang,
J. Zhang,
B. Zhao,
Z. W. Zhao
[show abstract]
[hide abstract]
ABSTRACT: The exclusive electroproduction process e⃗p→e'nπ+ was measured in the range of the photon virtuality Q2=1.7-4.5 GeV2, and the invariant mass range for the nπ+ system of W=1.15-1.7 GeV using the CEBAF Large Acceptance Spectrometer. For the first time, these kinematics are probed in exclusive π+ production from protons with nearly full coverage in the azimuthal and polar angles of the nπ+ center-of-mass system. The nπ+ channel has particular sensitivity to the isospin ½ excited nucleon states, and together with the pπ0 final state will serve to determine the transition form factors of a large number of resonances. The largest discrepancy between these results and present modes was seen in the σLT' structure function. In this experiment, 31,295 cross section and 4,184 asymmetry data points were measured. Because of the large volume of data, only a reduced set of structure functions and Legendre polynomial moments can be presented that are obtained in model-independent fits to the differential cross sections.
Phys. Rev. C. 01/2008; 77(1).
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H. Denizli,
J. Mueller,
S. Dytman,
M. L. Leber,
R. D. Levine,
J. Miles,
K. Y. Kim,
G. Adams,
M. J. Amaryan,
P. Ambrozewicz, [......],
D. P. Weygand,
M. Williams,
E. Wolin,
M. H. Wood,
A. Yegneswaran,
J. Yun,
L. Zana,
J. Zhang,
B. Zhao,
Z. W. Zhao
[show abstract]
[hide abstract]
ABSTRACT: New cross sections for the reaction ep→e'ηp are reported for total center-of-mass energy W=1.5-2.3 GeV and invariant squared momentum transfer Q2=0.13-3.3 GeV2. This large kinematic range allows the extraction of new information about response functions, photocouplings, and ηN coupling strengths of baryon resonances. A sharp structure is seen at W~1.7 GeV. The shape of the differential cross section is indicative of the presence of a P-wave resonance that persists to high Q2. Improved values are derived for the photocoupling amplitude for the S11(1535) resonance. The new data greatly expand the Q2 range covered, and an interpretation of all data with a consistent parametrization is provided.
Phys. Rev. C. 07/2007; 76(1).
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K S Egiyan,
G Asryan,
N Gevorgyan,
K A Griffioen,
J M Laget,
S E Kuhn,
G Adams,
M J Amaryan,
P Ambrozewicz,
M Anghinolfi, [......],
L B Weinstein,
D P Weygand,
M Williams,
E Wolin,
M H Wood,
A Yegneswaran,
L Zana,
J Zhang,
B Zhao,
Z W Zhao
[show abstract]
[hide abstract]
ABSTRACT: The reaction 2H(e,e'p)n has been studied with full kinematic coverage for photon virtuality 1.75<Q2<5.5 GeV2. Comparisons of experimental data with theory indicate that for very low values of neutron recoil momentum (p(n)<100 MeV/c) the neutron is primarily a spectator and the reaction can be described by the plane-wave impulse approximation. For 100<p(n)<750 MeV/c, proton-neutron rescattering dominates the cross section, while Delta production followed by the NDelta-->NN transition is the primary contribution at higher momenta.
Physical Review Letters 06/2007; 98(26):262502. · 7.37 Impact Factor
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P. Ambrozewicz,
D. S. Carman,
R. J. Feuerbach,
M. D. Mestayer,
B. A. Raue,
R. A. Schumacher,
A. Tkabladze,
M. J. Amarian,
M. Anghinolfi,
B. Asavapibhop, [......],
D. P. Weygand,
M. Williams,
E. Wolin,
M. H. Wood,
A. Yegneswaran,
J. Yun,
L. Zana,
J. Zhang,
B. Zhao,
Z. W. Zhao
[show abstract]
[hide abstract]
ABSTRACT: We report measurements of the exclusive electroproduction of K+Λ and K+Σ0 final states from a proton target using the Continuous Electron Beam Accelerator Facility (CEBAF) large-acceptance spectrometer (CLAS) detector at the Thomas Jefferson National Accelerator Facility. The separated structure functions σT,σL,σTT, and σLT were extracted from the Φ- and ε-dependent differential cross sections taken with electron beam energies of 2.567, 4.056, and 4.247 GeV. This analysis represents the first σL/σT separation with the CLAS detector, and the first measurement of the kaon electroproduction structure functions away from parallel kinematics. The data span a broad range of momentum transfers from 0.5⩽Q2⩽2.8GeV2 and invariant energy from 1.6⩽W⩽2.4 GeV, while spanning nearly the full center-of-mass angular range of the kaon. The separated structure functions reveal clear differences between the production dynamics for the Λ and Σ0 hyperons. These results provide an unprecedented data sample with which to constrain current and future models for the associated production of strangeness, which will allow for a better understanding of the underlying resonant and nonresonant contributions to hyperon production.
Phys. Rev. C. 04/2007; 75(4).
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R. K. Bradford,
R. A. Schumacher,
G. Adams,
M. J. Amaryan,
P. Ambrozewicz,
E. Anciant,
M. Anghinolfi,
B. Asavapibhop,
G. Asryan,
G. Audit, [......],
D. P. Weygand,
M. Williams,
E. Wolin,
M. H. Wood,
A. Yegneswaran,
J. Yun,
L. Zana,
J. Zhang,
B. Zhao,
Z. W. Zhao
[show abstract]
[hide abstract]
ABSTRACT: Spin transfer from circularly polarized real photons to recoiling hyperons has been measured for the reactions γ⃗+p→K++Λ⃗ and γ⃗+p→K++Σ⃗0. The data were obtained using the CEBAF Large Acceptance Spectrometer (CLAS) detector at the Jefferson Lab for center-of-mass energies W between 1.6 and 2.53 GeV, and for -0.85<cosθK+c.m.<+0.95. For the Λ, the polarization transfer coefficient along the photon momentum axis, Cz, was found to be near unity for a wide range of energy and kaon production angles. The associated transverse polarization coefficient Cx is smaller than Cz by a roughly constant difference of unity. Most significantly, the total Λ polarization vector, including the induced polarization P, has magnitude consistent with unity at all measured energies and production angles when the beam is fully polarized. For the Σ0 this simple phenomenology does not hold. All existing hadrodynamic models are in poor agreement with these results.
Phys. Rev. C. 03/2007; 75(3).
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P. E. Bosted,
K. V. Dharmawardane,
G. E. Dodge,
T. A. Forest,
S. E. Kuhn,
Y. Prok,
G. Adams,
M. Amarian,
P. Ambrozewicz,
M. Anghinolfi, [......],
D. P. Weygand,
M. Williams,
E. Wolin,
M. H. Wood,
A. Yegneswaran,
J. Yun,
L. Zana,
J. Zhang,
B. Zhao,
Z. Zhao
[show abstract]
[hide abstract]
ABSTRACT: New measurements of the spin structure functions of the proton and deuteron g1p(x,Q2) and g1d(x,Q2) in the nucleon resonance region are compared with extrapolations of target-mass-corrected next-to-leading-order (NLO) QCD fits to higher energy data. Averaged over the entire resonance region (W<2 GeV), the data and QCD fits are in good agreement in both magnitude and Q2 dependence for Q2>1.7 GeV2/c2. This “global” duality appears to result from cancellations among the prominent “local” resonance regions: in particular strong σ3/2 contributions in the Δ(1232) region appear to be compensated by strong σ1/2 contributions in the resonance region centered on 1.5 GeV. These results are encouraging for the extension of NLO QCD fits to lower W and Q2 than have been used previously.
Phys. Rev. C. 03/2007; 75(3).
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M Ungaro,
P Stoler,
I Aznauryan,
V D Burkert,
K Joo,
L C Smith,
G Adams,
M Amarian,
P Ambrozewicz,
M Anghinolfi, [......],
L B Weinstein,
D P Weygand,
M Williams,
E Wolin,
M H Wood,
A Yegneswaran,
L Zana,
B Zhang,
J Zhang,
B Zhao
[show abstract]
[hide abstract]
ABSTRACT: We report a new measurement of the exclusive electroproduction reaction gamma(*)p-->pi(0)p to explore the evolution from soft nonperturbative physics to hard processes via the Q(2) dependence of the magnetic (M(1+)), electric (E(1+)), and scalar (S(1+)) multipoles in the N-->Delta transition. 9000 differential cross section data points cover W from threshold to 1.4 GeV/c(2), 4pi center-of-mass solid angle, and Q(2) from 3 to 6 GeV(2)/c(2), the highest yet achieved. It is found that the magnetic form factor G(M)(*) decreases with Q(2) more steeply than the proton magnetic form factor, the ratio E(1+)/M(1+) is small and negative, indicating strong helicity nonconservation, and the ratio S(1+)/M(1+) is negative, while its magnitude increases with Q(2).
Physical Review Letters 09/2006; 97(11):112003. · 7.37 Impact Factor
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S Chen,
H Avakian,
V D Burkert,
P Eugenio,
G Adams,
M Amarian,
P Ambrozewicz,
M Anghinolfi,
G Asryan,
H Bagdasaryan, [......],
D P Weygand,
M Williams,
E Wolin,
M H Wood,
A Yegneswaran,
J Yun,
L Zana,
J Zhang,
B Zhao,
Z Zhao
[show abstract]
[hide abstract]
ABSTRACT: The longitudinal target-spin asymmetry AUL for the exclusive electroproduction of high-energy photons was measured for the first time in ep-->e;'pgamma. The data have been accumulated at JLab with the CLAS spectrometer using 5.7 GeV electrons and a longitudinally polarized NH3 target. A significant azimuthal angular dependence was observed, resulting from the interference of the deeply virtual Compton scattering and Bethe-Heitler processes. The amplitude of the sinvarphi moment is 0.252+/-0.042stat+/-0.020sys. Theoretical calculations are in good agreement with the magnitude and the kinematic dependence of the target-spin asymmetry, which is sensitive to the generalized parton distributions H and H.
Physical Review Letters 08/2006; 97(7):072002. · 7.37 Impact Factor
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M. Osipenko,
G. Ricco,
S. Simula,
M. Battaglieri,
M. Ripani,
G. Adams,
P. Ambrozewicz,
M. Anghinolfi,
B. Asavapibhop,
G. Asryan, [......],
A. V. Vlassov,
L. B. Weinstein,
D. P. Weygand,
M. Williams,
E. Wolin,
M. H. Wood,
A. Yegneswaran,
J. Yun,
L. Zana,
J. Zhang
[show abstract]
[hide abstract]
ABSTRACT: Inclusive electron scattering off the deuteron has been measured to extract the deuteron structure function F2 with the CEBAF Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility. The measurement covers the entire resonance region from the quasielastic peak up to the invariant mass of the final-state hadronic system W≃2.7 GeV with four-momentum transfers Q2 from 0.4 to 6 (GeV/c)2. These data are complementary to previous measurements of the proton structure function F2 and cover a similar two-dimensional region of Q2 and Bjorken variable x. Determination of the deuteron F2 over a large x interval including the quasielastic peak as a function of Q2, together with the other world data, permit a direct evaluation of the structure function moments for the first time. By fitting the Q2 evolution of these moments with an OPE-based twist expansion we have obtained a separation of the leading twist and higher twist terms. The observed Q2 behavior of the higher twist contribution suggests a partial cancelation of different higher twists entering into the expansion with opposite signs. This cancelation, found also in the proton moments, is a manifestation of the “duality” phenomenon in the F2 structure function.
Phys. Rev. C. 04/2006; 73(4).
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R. Bradford,
R. A. Schumacher,
J. W. C. McNabb,
L. Todor,
G. Adams,
P. Ambrozewicz,
E. Anciant,
M. Anghinolfi,
B. Asavapibhop,
G. Asryan, [......],
H. Weller,
D. P. Weygand,
M. Williams,
E. Wolin,
M. H. Wood,
A. Yegneswaran,
J. Yun,
L. Zana,
J. Zhang,
B. Zhao
[show abstract]
[hide abstract]
ABSTRACT: High-statistics cross sections for the reactions γ+p→K++Λ and γ+p→K++Σ0 have been measured using CLAS at Jefferson Lab for center-of-mass energies W between 1.6 and 2.53 GeV, and for -0.85<cosθK+c.m.<+0.95. In the K+Λ channel we confirm a resonance-like structure near W=1.9 GeV at backward kaon angles. The position and width of this structure change with angle, indicating that more than one resonance is likely playing a role. The K+Λ channel at forward angles and all energies is well described by a t-channel scaling characteristic of Regge exchange, whereas the same scaling applied to the K+Σ0 channel is less successful. Several existing theoretical models are compared to the data, but none provide a good representation of the results.
Phys. Rev. C. 03/2006; 73(3).
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H. Egiyan,
I. G. Aznauryan,
V. D. Burkert,
K. A. Griffioen,
K. Joo,
R. Minehart,
L. C. Smith,
G. Adams,
P. Ambrozewicz,
E. Anciant, [......],
H. Weller,
D. P. Weygand,
C. S. Whisnant,
E. Wolin,
M. H. Wood,
A. Yegneswaran,
J. Yun,
J. Zhang,
J. Zhao,
Z. Zhou
[show abstract]
[hide abstract]
ABSTRACT: The ep→e'π+n reaction was studied in the first and second nucleon resonance regions in the 0.25 GeV2<Q2<0.65 GeV2 range by use of the CLAS detector at Thomas Jefferson National Accelerator Facility. For the first time, to our knowledge, the absolute cross sections were measured, covering nearly the full angular range in the hadronic center-of-mass frame. We extracted the structure functions σTL,σTT, and the linear combination σT+εσL by fitting the ϕ dependence of the measured cross sections and compared them with the MAID and Sato-Lee models.
Phys. Rev. C. 02/2006; 73(2).
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H. Egiyan,
I. G. Aznauryan,
V. D. Burkert,
K. A. Griffioen,
K. Joo,
R. Minehart,
L. C. Smith,
G. Adams,
P. Ambrozewicz,
E. Anciant, [......],
H. Weller,
D. P. Weygand,
C. S. Whisnant,
E. Wolin,
M. H. Wood,
A. Yegneswaran,
J. Yun,
J. Zhang,
J. Zhao,
Z. Zhou
[show abstract]
[hide abstract]
ABSTRACT: The ep→e'π+n reaction was studied in the first and second nucleon resonance regions in the 0.25 GeV2<Q2<0.65 GeV2 range by use of the CLAS detector at Thomas Jefferson National Accelerator Facility. For the first time, to our knowledge, the absolute cross sections were measured, covering nearly the full angular range in the hadronic center-of-mass frame. We extracted the structure functions σTL,σTT, and the linear combination σT+εσL by fitting the ϕ dependence of the measured cross sections and compared them with the MAID and Sato-Lee models.
Phys. Rev. C. 02/2006; 73(2).
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M Dugger,
J P Ball,
P Collins,
E Pasyuk,
B G Ritchie,
G Adams,
P Ambrozewicz,
E Anciant,
M Anghinolfi,
B Asavapibhop, [......],
L B Weinstein,
H Weller,
D P Weygand,
M Williams,
E Wolin,
M H Wood,
A Yegneswaran,
J Yun,
L Zana,
J Zhang
[show abstract]
[hide abstract]
ABSTRACT: Differential cross sections for the reaction gamma p --> eta' p have been measured with the CLAS spectrometer and a tagged photon beam with energies from 1.527 to 2.227 GeV. The results reported here possess much greater accuracy than previous measurements. Analyses of these data suggest for the first time the coupling of the eta'N channel to both the S11(1535) and P11(1710) resonances, known to couple strongly to the etaN channel in photoproduction on the proton, and the importance of J = 3/2 resonances in the process.
Physical Review Letters 02/2006; 96(6):062001. · 7.37 Impact Factor
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S Strauch,
B L Berman,
G Adams,
P Ambrozewicz,
M Anghinolfi,
B Asavapibhop,
G Asryan,
G Audit,
H Avakian,
H Bagdasaryan, [......],
K Wang,
L B Weinstein,
D P Weygand,
M Williams,
E Wolin,
M H Wood,
A Yegneswaran,
J Yun,
L Zana,
J Zhang
[show abstract]
[hide abstract]
ABSTRACT: Beam-helicity asymmetries for the two-pion-photoproduction reaction gammap-->ppi(+)pi(-) have been studied for the first time in the resonance region for center-of-mass energies between 1.35 and 2.30 GeV. The experiment was performed at Jefferson Lab with the CEBAF Large Acceptance Spectrometer using circularly polarized tagged photons incident on an unpolarized hydrogen target. Beam-helicity-dependent angular distributions of the final-state particles were measured. The large cross-section asymmetries exhibit strong sensitivity to the kinematics and dynamics of the reaction. The data are compared with the results of various phenomenological model calculations, and show that these models currently do not provide an adequate description for the behavior of this new observable.
Physical Review Letters 10/2005; 95(16):162003. · 7.37 Impact Factor
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S. Taylor,
G. S. Mutchler,
G. Adams,
P. Ambrozewicz,
E. Anciant,
M. Anghinolfi,
B. Asavapibhop,
G. Asryan,
G. Audit,
H. Avakian, [......],
L. B. Weinstein,
H. Weller,
D. P. Weygand,
C. S. Whisnant,
M. Williams,
E. Wolin,
M. H. Wood,
A. Yegneswaran,
J. Yun,
L. Zana
Physical Review C 08/2005; 72(3):39902. · 3.31 Impact Factor
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P Rossi,
M Mirazita,
F Ronchetti,
E De Sanctis,
G Adams,
P Ambrozewicz,
E Anciant,
M Anghinolfi,
B Asavapibhop,
G Audit, [......],
L B Weinstein,
H Weller,
D P Weygand,
C S Whisnant,
E Wolin,
M H Wood,
A Yegneswaran,
J Yun,
B Zhang,
Z Zhou
[show abstract]
[hide abstract]
ABSTRACT: We investigate the transition from the nucleon-meson to the quark-gluon description of the strong interaction using the photon energy dependence of the d(gamma,p)n differential cross section for photon energies above 0.5 GeV and center-of-mass proton angles between 30 degrees and 150 degrees. A possible signature for this transition is the onset of cross-section s(-11) scaling with the total energy squared, s, at some proton transverse momentum P(T). The results show that the scaling has been reached for proton transverse momentum above about 1.1 GeV/c. This may indicate that the quark-gluon regime is reached above this momentum.
Physical Review Letters 02/2005; 94(1):012301. · 7.37 Impact Factor
