-
C. S. Nepali,
M. Amaryan,
K. P. Adhikari,
M. Aghasyan,
S. Anefalos Pereira,
H. Baghdasaryan,
J. Ball,
M. Battaglieri,
V. Batourine,
I. Bedlinskiy, [......],
E. Voutier,
N. K. Walford,
D. P. Watts,
L. B. Weinstein,
D. P. Weygand,
N. Zachariou,
L. Zana,
J. Zhang,
Z. W. Zhao,
I. Zonta
[show abstract]
[hide abstract]
ABSTRACT: Experimental results on the $\Sigma^+(1189)$ hyperon transverse polarization
in photoproduction on a hydrogen target using the CLAS detector at Jefferson
laboratory are presented. The $\Sigma^+(1189)$ was reconstructed in the
exclusive reaction $\gamma+p\rightarrow K^{0}_{S} + \Sigma^+(1189)$ via the
$\Sigma^{+} \to p \pi^{0}$ decay mode. The $K^{0}_S$ was reconstructed in the
invariant mass of two oppositely charged pions with the $\pi^0$ identified in
the missing mass of the detected $p\pi^+\pi^-$ final state. Experimental data
were collected in the photon energy range $E_{\gamma}$ = 1.0-3.5 GeV
($\sqrt{s}$ range 1.66-2.73 GeV). We observe a large negative polarization of
up to 95%. As the mechanism of transverse polarization of hyperons produced in
unpolarized photoproduction experiments is still not well understood, these
results will help to distinguish between different theoretical models on
hyperon production and provide valuable information for the searches of missing
baryon resonances.
02/2013;
-
The CLAS Collaboration,
Y. Ilieva,
B. L. Berman,
A. E. Kudryavtsev,
I. I. Strakovsky,
V. E. Tarasov,
M. Amarian,
P. Ambrozewicz,
M. Anghinolfi,
G. Asryan, [......],
L. B. Weinstein,
D. P. Weygand,
M. Williams,
E. Wolin,
M. H. Wood,
A. Yegneswaran,
L. Zana,
J. Zhang,
B. Zhao,
Z. Zhao
[show abstract]
[hide abstract]
ABSTRACT: High-quality cross sections for the reaction γd → π0
d have been measured using the CLAS at Jefferson Lab over a wide energy range near and above the η-meson photoproduction threshold. At backward c.m. angles for the outgoing pions, we observe a resonance-like structure near
E
γ = 700 MeV. Our model analysis shows that it can be explained by η excitation in the intermediate state. The effect is the result of the contribution of the N(1535)S
11-resonance to the amplitudes of the subprocesses occurring between the two nucleons and of a two-step process in which the
excitation of an intermediate η-meson dominates.
European Physical Journal A 04/2012; 43(3):261-267. · 2.19 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We report preliminary data on proton-lambda correlations at small relative momentum q in the e
3He(4He) → e′pΛX reaction at E
0 = 4.7(4.46) GeV using the CLAS detector at Jefferson Lab. The enhancement of the correlation function at small q was found to be in qualitative agreement with theoretical expectations. The size of emission region about 1.5 fm was estimated
using Lednický-Lyuboshitz analytical model. The experimental correlation function is comparable with the P-matrix fit of the hyperon-nucleon data. Small-relative-momentum-proton-lambda correlations both for 3He(4He) target and for electroproduction reaction were studied for the first time.
Physics of Atomic Nuclei 04/2012; 72(4):668-674. · 0.57 Impact Factor
-
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
-
M Battaglieri,
R De Vita,
A P Szczepaniak,
K P Adhikari,
M Aghasyan,
M J Amaryan,
P Ambrozewicz,
M Anghinolfi,
G Asryan,
H Avakian, [......],
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: We report on the results of the first measurement of exclusive f_{0}(980) meson photoproduction on protons for E_{gamma}=3.0-3.8 GeV and -t=0.4-1.0 GeV2. Data were collected with the CLAS detector at the Thomas Jefferson National Accelerator Facility. The resonance was detected via its decay in the pi;{+}pi;{-} channel by performing a partial wave analysis of the reaction gammap-->ppi;{+}pi;{-}. Clear evidence of the f_{0}(980) meson was found in the interference between P and S waves at M_{pi;{+}pi;{-}} approximately 1 GeV. The S-wave differential cross section integrated in the mass range of the f_{0}(980) was found to be a factor of about 50 smaller than the cross section for the rho meson. This is the first time the f_{0}(980) meson has been measured in a photoproduction experiment.
Physical Review Letters 04/2009; 102(10):102001. · 7.37 Impact Factor
-
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
-
G. V. Fedotov,
V. I. Mokeev,
V. D. Burkert,
L. Elouadrhiri,
E. N. Golovatch,
B. S. Ishkhanov,
E. L. Isupov,
N. V. Shvedunov,
G. Adams,
M. J. Amaryan, [......],
M. F. Vineyard, A. V. Vlassov,
L. B. Weinstein,
D. P. Weygand,
M. Williams,
E. Wolin,
M. H. Wood,
A. Yegneswaran,
L. Zana,
J. Zhang
[show abstract]
[hide abstract]
ABSTRACT: This paper reports on the most comprehensive data set obtained on differential and fully integrated cross sections for the process ep→e'pπ+π-. The data were collected with the CLAS detector at Jefferson Laboratory. Measurements were carried out in the as yet unexplored kinematic region of photon virtuality 0.2<Q2<0.6 GeV2 and invariant mass of the final hadron system W from 1.3 to 1.57 GeV. For the first time, nine independent one-fold differential cross sections were determined in each bin of W and Q2 covered by the measurements. A phenomenological analysis of the data allowed us to establish the most significant mechanisms contributing to the reaction. The nonresonant mechanisms account for a major part of cross sections. However, we find sensitivity to s-channel excitations of low-mass nucleon resonances, especially to the N(1440)P11 and N(1520)D13 states in kinematic dependencies of the one-fold differential cross sections.
Phys. Rev. C. 01/2009; 79(1).
-
G. V. Fedotov,
V. I. Mokeev,
V. D. Burkert,
L. Elouadrhiri,
E. N. Golovatch,
B. S. Ishkhanov,
E. L. Isupov,
N. V. Shvedunov,
G. Adams,
M. J. Amaryan, [......],
M. F. Vineyard, A. V. Vlassov,
L. B. Weinstein,
D. P. Weygand,
M. Williams,
E. Wolin,
M. H. Wood,
A. Yegneswaran,
L. Zana,
J. Zhang
[show abstract]
[hide abstract]
ABSTRACT: This paper reports on the most comprehensive data set obtained on differential and fully integrated cross sections for the process ep→e'pπ+π-. The data were collected with the CLAS detector at Jefferson Laboratory. Measurements were carried out in the as yet unexplored kinematic region of photon virtuality 0.2<Q2<0.6 GeV2 and invariant mass of the final hadron system W from 1.3 to 1.57 GeV. For the first time, nine independent one-fold differential cross sections were determined in each bin of W and Q2 covered by the measurements. A phenomenological analysis of the data allowed us to establish the most significant mechanisms contributing to the reaction. The nonresonant mechanisms account for a major part of cross sections. However, we find sensitivity to s-channel excitations of low-mass nucleon resonances, especially to the N(1440)P11 and N(1520)D13 states in kinematic dependencies of the one-fold differential cross sections.
Phys. Rev. C. 01/2009; 79(1).
-
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
-
A. S. Biselli,
V. D. Burkert,
M. J. Amaryan,
G. Asryan,
H. Avakian,
H. Bagdasaryan,
N. Baillie,
J. P. Ball,
N. A. Baltzell,
M. Battaglieri, [......],
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 exclusive channel p⃗(e⃗,e'p)π0 was studied in the first and second nucleon resonance regions in the Q2 range from 0.187 to 0.770 GeV2 at Jefferson Lab using the CEBAF Large Acceptance Spectrometer. Longitudinal target and beam-target asymmetries were extracted over a large range of center-of-mass angles of the π0 and compared to the unitary isobar model MAID, the dynamic model by Sato and Lee, and the dynamic model DMT. A strong sensitivity to individual models was observed, in particular for the target asymmetry and in the higher invariant mass region. This data set, once included in the global fits of the above models, is expected to place strong constraints on the electrocoupling amplitudes A1/2 and S1/2 for the Roper resonance N(1400)P11 and the N(1535)S11 and N(1520)D13 states.
Phys. Rev. C. 10/2008; 78(4).
-
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).
-
F X Girod,
R A Niyazov,
H Avakian,
J Ball,
I Bedlinskiy,
V D Burkert,
R De Masi,
L Elouadrhiri,
M Garçon,
M Guidal, [......],
D P Watts,
L B Weinstein,
D P Weygand,
M Williams,
E Wolin,
M H Wood,
A Yegneswaran,
L Zana,
J Zhang,
Z W Zhao
[show abstract]
[hide abstract]
ABSTRACT: The beam-spin asymmetries in the hard exclusive electroproduction of photons on the proton (e p-->epgamma) were measured over a wide kinematic range and with high statistical accuracy. These asymmetries result from the interference of the Bethe-Heitler process and of deeply virtual Compton scattering. Over the whole kinematic range (x(B) from 0.11 to 0.58, Q2 from 1 to 4.8 GeV2, -t from 0.09 to 1.8 GeV2), the azimuthal dependence of the asymmetries is compatible with expectations from leading-twist dominance, A approximately a sinphi/(1+c cosphi). This extensive set of data can thus be used to constrain significantly the generalized parton distributions of the nucleon in the valence quark sector.
Physical Review Letters 04/2008; 100(16):162002. · 7.37 Impact Factor
-
D G Ireland,
B McKinnon,
D Protopopescu,
P Ambrozewicz,
M Anghinolfi,
G Asryan,
H Avakian,
H Bagdasaryan,
N Baillie,
J P Ball, [......],
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: We examine the results of two measurements by the CLAS collaboration, one of which claimed evidence for a Theta(+) pentaquark, while the other found no such evidence. The unique feature of these two experiments was that they were performed with the same experimental setup. Using a Bayesian analysis, we find that the results of the two experiments are in fact compatible with each other, but that the first measurement did not contain sufficient information to determine unambiguously the existence of a Theta(+). Further, we suggest a means by which the existence of a new candidate particle can be tested in a rigorous manner.
Physical Review Letters 03/2008; 100(5):052001. · 7.37 Impact Factor
-
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).
-
R Nasseripour,
M H Wood,
C Djalali,
D P Weygand,
C Tur,
U Mosel,
P Muehlich,
G Adams,
M J Amaryan,
P Ambrozewicz, [......],
D P Watts,
L B Weinstein,
M Williams,
E Wolin,
A Yegneswaran,
L Zana,
B Zhang,
J Zhang,
B Zhao,
Z W Zhao
[show abstract]
[hide abstract]
ABSTRACT: The photoproduction of vector mesons on various nuclei has been studied using the CLAS detector at Jefferson Laboratory. The vector mesons, rho, omega, and varphi, are observed via their decay to e;{+}e;{-}, in order to reduce the effects of final-state interactions in the nucleus. Of particular interest are possible in-medium effects on the properties of the rho meson. The rho mass spectrum is extracted from the data on various nuclei, 2H, C, Fe, and Ti. We observe no significant mass shift and some broadening consistent with expected collisional broadening for the rho meson.
Physical Review Letters 01/2008; 99(26):262302. · 7.37 Impact Factor
-
I. Hleiqawi,
K. Hicks,
D. S. Carman,
T. Mibe,
G. Niculescu,
A. Tkabladze,
M. Amarian,
P. Ambrozewicz,
M. Anghinolfi,
G. Asryan, [......],
D. P. Weygand,
S. Whisnant,
M. Williams,
E. Wolin,
M. H. Wood,
A. Yegneswaran,
L. Zana,
J. Zhang,
B. Zhao,
Z. Zhao
Physical Review C 08/2007; 76(3):39905. · 3.31 Impact Factor
-
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).
-
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
-
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).
-
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).
