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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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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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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. 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
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Clas Collaboration,
D. Protopopescu,
F. W. Hersman,
M. Holtrop,
G. Adams,
P. Ambrozewicz, E. Anciant,
M. Anghinolfi,
B. Asavapibhop,
G. Asryan, [......],
H. Weller,
D. P. Weygand,
C. S. Whisnant,
M. Williams,
E. Wolin,
M. H. Wood,
A. Yegneswaran,
J. Yun,
L. Zana,
B. Zhang
[show abstract]
[hide abstract]
ABSTRACT: Single spin azimuthal asymmetries ALT′ were
measured at Jefferson Lab using 2.2 and 4.4 GeV longitudinally polarised
electrons incident on 4He and 12C targets in the
CLAS detector. ALT′ is related to the
imaginary part of the longitudinal-transverse interference and in
quasifree nucleon knockout it provides an unambiguous signature for
final state interactions (FSI). Experimental values of
ALT′ were found to be below 5%, typically
|ALT′|⩽3% for data with good statistical
precision. Optical model in eikonal approximation (OMEA) and
relativistic multiple-scattering Glauber approximation (RMSGA)
calculations are shown to be consistent with the measured asymmetries.
Nuclear Physics A 01/2005; 748:357-373. · 1.54 Impact Factor
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A V Stavinsky,
K R Mikhailov,
R Lednicky,
A V Vlassov,
G Adams,
P Ambrozewich, E Anciant,
M Anghinolfi,
B Asavapibhop,
G Asryan, [......],
L B Weinstein,
H Weller,
D P Weygand,
C S Whisnant,
M Williams,
E Wolin,
M H Wood,
A Yegneswaran,
J Yun,
L Zana
[show abstract]
[hide abstract]
ABSTRACT: Two-proton correlations at small relative momentum q were studied in the eA(3He,4He,C,Fe)-->e(')ppX reaction at E(0)=4.46 GeV using the CLAS detector at Jefferson Lab. The enhancement of the correlation function at small q was found to be in accordance with theoretical expectations. Sizes of the emission region were extracted, and proved to be dependent on A and on the proton momentum. The size of the two-proton emission region for He was measured in eA reactions for the first time.
Physical Review Letters 11/2004; 93(19):192301. · 7.37 Impact Factor
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M. Mirazita,
F. Ronchetti,
P. Rossi,
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: Nearly complete angular distributions of the two-body deuteron photodisintegration differential cross section have been measured using the CEBAF Large Acceptance Spectrometer detector and the tagged photon beam at the Thomas Jefferson National Accelerator Facility. The data cover photon energies between 0.5 and 3.0 GeV and center-of-mass proton scattering angles 10°–160°. The data show a persistent forward-backward angle asymmetry over the explored energy range, and are well described by the nonperturbative quark gluon string model.
Phys. Rev. C. 07/2004; 70(1).
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R A Niyazov,
L B Weinstein,
G Adams,
P Ambrozewicz, E Anciant,
M Anghinolfi,
B Asavapibhop,
G Asryan,
G Audit,
T Auger, [......],
A V Vlassov,
K Wang,
H Weller,
D P Weygand,
C S Whisnant,
E Wolin,
M H Wood,
A Yegneswaran,
J Yun,
B Zhang
[show abstract]
[hide abstract]
ABSTRACT: We have measured the 3He(e,e'pp)n reaction at 2.2 GeV over a wide kinematic range. The kinetic energy distribution for "fast" nucleons (p>250 MeV/c) peaks where two nucleons each have 20% or less, and the third nucleon has most of the transferred energy. These fast pp and pn pairs are back to back with little momentum along the three-momentum transfer, indicating that they are spectators. Calculations by Sargsian and by Laget also indicate that we have measured distorted two-nucleon momentum distributions by striking one nucleon and detecting the spectator correlated pair.
Physical Review Letters 02/2004; 92(5):052303. · 7.37 Impact Factor
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V Kubarovsky,
L Guo,
D P Weygand,
P Stoler,
M Battaglieri,
R DeVita,
G Adams,
Ji Li,
M Nozar,
C Salgado, [......],
M F Vineyard,
A V Vlassov,
K Wang,
L B Weinstein,
A Weisberg,
C S Whisnant,
E Wolin,
M H Wood,
A Yegneswaran,
J Yun
[show abstract]
[hide abstract]
ABSTRACT: The reaction gamma p-->pi(+)K(-)K(+)n was studied at Jefferson Laboratory using a tagged photon beam with an energy range of 3-5.47 GeV. A narrow baryon state with strangeness S=+1 and mass M=1555+/-10 MeV/c(2) was observed in the nK(+) invariant mass spectrum. The peak's width is consistent with the CLAS resolution (FWHM=26 MeV/c(2)), and its statistical significance is (7.8+/-1.0)sigma. A baryon with positive strangeness has exotic structure and cannot be described in the framework of the naive constituent quark model. The mass of the observed state is consistent with the mass predicted by the chiral soliton model for the Theta(+) baryon. In addition, the pK(+) invariant mass distribution was analyzed in the reaction gamma p-->K(-)K(+)p with high statistics in search of doubly charged exotic baryon states. No resonance structures were found in this spectrum.
Physical Review Letters 01/2004; 92(3):032001. · 7.37 Impact Factor
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S Stepanyan,
K Hicks,
D S Carman,
E Pasyuk,
R A Schumacher,
E S Smith,
D J Tedeschi,
L Todor,
G Adams,
P Ambrozewicz, [......],
A V Vlassov,
K Wang,
L B Weinstein,
H Weller,
D P Weygand,
C S Whisnant,
E Wolin,
M H Wood,
A Yegneswaran,
J Yun
[show abstract]
[hide abstract]
ABSTRACT: In an exclusive measurement of the reaction gammad-->K(+)K(-)pn, a narrow peak that can be attributed to an exotic baryon with strangeness S=+1 is seen in the K(+)n invariant mass spectrum. The peak is at 1.542+/-0.005 GeV/c(2) with a measured width of 0.021 GeV/c(2) FWHM, which is largely determined by experimental mass resolution. The statistical significance of the peak is (5.2+/-0.6)sigma. The mass and width of the observed peak are consistent with recent reports of a narrow S=+1 baryon by other experimental groups.
Physical Review Letters 12/2003; 91(25):252001. · 7.37 Impact Factor
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R Fatemi,
A V Skabelin,
V D Burkert,
D Crabb,
R De Vita,
S E Kuhn,
R Minehart,
G Adams, E Anciant,
M Anghinolfi, [......],
H Weller,
D P Weygand,
C S Whisnant,
E Wolin,
M H Wood,
A Yegneswaran,
J Yun,
B Zhang,
J Zhao,
Z Zhou
[show abstract]
[hide abstract]
ABSTRACT: Double-polarization asymmetries for inclusive ep scattering were measured at Jefferson Lab using 2.6 and 4.3 GeV longitudinally polarized electrons incident on a longitudinally polarized NH3 target in the CLAS detector. The polarized structure function g(1)(x,Q2) was extracted throughout the nucleon resonance region and into the deep inelastic regime, for Q(2)=0.15-1.64 GeV2. The contributions to the first moment Gamma(1)(Q2)= integral g(1)(x,Q2) dx were determined up to Q(2)=1.2 GeV2. Using a parametrization for g(1) in the unmeasured low x regions, the complete first moment was estimated over this Q2 region. A rapid change in Gamma(1) is observed for Q2<1 GeV2, with a sign change near Q(2)=0.3 GeV2, indicating dominant contributions from the resonance region. At Q(2)=1.2 GeV2 our data are below the perturbative QCD evolved scaling value.
Physical Review Letters 11/2003; 91(22):222002. · 7.37 Impact Factor
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A. Biselli,
G. S. Adams,
M. J. Amaryan, E. Anciant,
M. Anghinolfi,
B. Asavapibhop,
G. Asryan,
G. Audit,
T. Auger,
H. Avakian, [......],
R. Welsh,
D. P. Weygand,
S. Whisnant,
M. Witkowski,
E. Wolin,
A. Yegneswaran,
J. Yun,
B. Zhang,
J. Zhao,
Z. Zhou
[show abstract]
[hide abstract]
ABSTRACT: Measurements of the angular distributions of target and double-spin asymmetries for the Δ+(1232) in the exclusive channel p⃗(e⃗,e′p)π0 obtained at the Jefferson Lab in the Q2 range from 0.5 to 1.5GeV2/c2 are presented. Results of the asymmetries are compared with the unitary isobar model [D. Drechsel et al., Nucl. Phys. A645, 145 (1999)], dynamical models [T. Sato and T. S. Lee, Phys. Rev. C 54, 2660 (1996); S. S. Kamalov et al., Phys. Lett. B 27, 522 (2001)], and the effective Lagrangian theory [R. M. Davidson et al., Phys. Rev. D 43, 71 (1991)]. Sensitivity to the different models was observed, particularly in relation to the description of background terms on which the target asymmetry depends significantly.
Phys. Rev. C. 09/2003; 68(3).
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K. Sh. Egiyan,
N. Dashyan,
M. Sargsian,
S. Stepanyan,
L. B. Weinstein,
G. Adams,
P. Ambrozewicz, E. Anciant,
M. Anghinolfi,
B. Asavapibhop, [......],
H. Weller,
D. P. Weygand,
C. S. Whisnant,
E. Wolin,
M. H. Wood,
A. Yegneswaran,
J. Yun,
B. Zhang,
J. Zhao,
Z. Zhou
[show abstract]
[hide abstract]
ABSTRACT: The ratios of inclusive electron scattering cross sections of 4He, 12C, and 56Fe to 3He have been measured for the first time. It is shown that these ratios are independent of xB at Q2>1.4GeV2 for xB>1.5, where the inclusive cross section depends primarily on the high momentum components of the nuclear wave function. The observed scaling shows that the momentum distributions at high-momenta have the same shape for all nuclei and differ only by a scale factor. The observed onset of the scaling at Q2>1.4GeV2 and xB>1.5 is consistent with the kinematical expectation that two-nucleon short range correlations (SRC) dominate the nuclear wave function at pm≳300MeV/c. The values of these ratios in the scaling region can be related to the relative probabilities of SRC in nuclei with A>~3. Our data, combined with calculations and other measurements of the 3He/deuterium ratio, demonstrate that for nuclei with A>~12 these probabilities are 4.9–5.9 times larger than in deuterium, while for 4He it is larger by a factor of about 3.8.
Phys. Rev. C. 07/2003; 68(1).
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M Ripani,
V D Burkert,
V Mokeev,
M Battaglieri,
R De Vita,
E Golovach,
M Taiuti,
G Adams, E Anciant,
M Anghinolfi, [......],
H Weller,
D P Weygand,
C S Whisnant,
E Wolin,
M H Wood,
A Yegneswaran,
J Yun,
B Zhang,
J Zhao,
Z Zhou
[show abstract]
[hide abstract]
ABSTRACT: The cross section for the reaction ep-->e(')ppi(+)pi(-) was measured in the resonance region for 1.4<W<2.1 GeV and 0.5<Q2<1.5 GeV(2)/c(2) using the CLAS detector at Jefferson Laboratory. The data show resonant structures not visible in previous experiments. The comparison of our data to a phenomenological prediction using available information on N(*) and Delta states shows an evident discrepancy. A better description of the data is obtained either by a sizable change of the properties of the P13(1720) resonance or by introducing a new baryon state, not reported in published analyses.
Physical Review Letters 07/2003; 91(2):022002. · 7.37 Impact Factor
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J. Yun,
S. E. Kuhn,
G. E. Dodge,
T. A. Forest,
M. Taiuti,
G. S. Adams,
M. J. Amaryan, E. Anciant,
M. Anghinolfi,
B. Asavapibhop, [......],
R. Welsh,
D. P. Weygand,
S. Whisnant,
M. Witkowski,
E. Wolin,
M. H. Wood,
A. Yegneswaran,
B. Zhang,
J. Zhao,
Z. Zhou
[show abstract]
[hide abstract]
ABSTRACT: We report the results of a new measurement of spin structure functions of the deuteron in the region of moderate momentum transfer [Q2=0.27–1.3(GeV/c)2] and final hadronic state mass in the nucleon resonance region (W=1.08–2.0GeV). We scattered a 2.5 GeV polarized continuous electron beam at Jefferson Lab off a dynamically polarized cryogenic solid state target (15ND3) and detected the scattered electrons with the CEBAF large acceptance spectrometer. From our data, we extract the longitudinal double spin asymmetry A|| and the spin structure function g1d. Our data are generally in reasonable agreement with existing data from SLAC where they overlap, and they represent a substantial improvement in statistical precision. We compare our results with expectations for resonance asymmetries and extrapolated deep inelastic scaling results. Finally, we evaluate the first moment of the structure function g1d and study its approach to both the deep inelastic limit at large Q2 and to the Gerasimov-Drell-Hearn sum rule at the real photon limit (Q2→0). We find that the first moment varies rapidly in the Q2 range of our experiment and crosses zero at Q2 between 0.5 and 0.8(GeV/c)2, indicating the importance of the Δ resonance at these momentum transfers.
Phys. Rev. C. 05/2003; 67(5).
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M. Osipenko,
G. Ricco,
M. Taiuti,
M. Ripani,
S. Simula,
G. Adams, E. Anciant,
M. Anghinolfi,
B. Asavapibhop,
G. Audit, [......],
H. Weller,
D. P. Weygand,
C. S. Whisnant,
E. Wolin,
M. H. Wood,
A. Yegneswaran,
J. Yun,
B. Zhang,
J. Zhao,
Z. Zhou
[show abstract]
[hide abstract]
ABSTRACT: We measured the inclusive electron-proton cross section in the nucleon resonance region (W<2.5GeV) at momentum transfers Q2 below 4.5(GeV/c)2 with the CLAS detector. The large acceptance of CLAS allowed the measurement of the cross section in a large, contiguous two-dimensional range of Q2 and x, making it possible to perform an integration of the data at fixed Q2 over the significant x interval. From these data we extracted the structure function F2 and, by including other world data, we studied the Q2 evolution of its moments, Mn(Q2), in order to estimate higher twist contributions. The small statistical and systematic uncertainties of the CLAS data allow a precise extraction of the higher twists and will require significant improvements in theoretical predictions if a meaningful comparison with these new experimental results is to be made.
Phys. Rev. D. 05/2003; 67(9).
