8 research outputs found
First measurement of the polarization observable E in the p→(γ→,π+)n reaction up to 2.25 GeV
First results from the longitudinally polarized frozen-spin target (FROST) program are reported. The double-polarization observable E, for the reaction γ p→π+n, has been measured using a circularly polarized tagged-photon beam, with energies from 0.35 to 2.37GeV. The final-state pions were detected with the CEBAF Large Acceptance Spectrometer in Hall B at the Thomas Jefferson National Accelerator Facility. These polarization data agree fairly well with previous partial-wave analyses at low photon energies. Over much of the covered energy range, however, significant deviations are observed, particularly in the high-energy region where high-Lmultipoles contribute. The data have been included in new multipole analyses resulting in updated nucleon resonance parameters. We report updated fits from the Bonn–Gatchina, Jülich–Bonn, and SAID groups
First measurement of the helicity asymmetry E in eta photoproduction on the proton
Results are presented for the first measurement of the double-polarization
helicity asymmetry E for the photoproduction reaction . Data were obtained using the FROzen Spin Target (FROST)
with the CLAS spectrometer in Hall B at Jefferson Lab, covering a range of
center-of-mass energy W from threshold to 2.15 GeV and a large range in
center-of-mass polar angle. As an initial application of these data, the
results have been incorporated into the J\"ulich model to examine the case for
the existence of a narrow resonance between 1.66 and 1.70 GeV. The
addition of these data to the world database results in marked changes in the
predictions for the E observable using that model. Further comparison with
several theoretical approaches indicates these data will significantly enhance
our understanding of nucleon resonances
Target and double spin asymmetries of deeply virtual pi(0) production with a longitudinally polarized proton target and CLAS
The target and double spin asymmetries of the exclusive pseudoscalar channel
were measured for the first time in the
deep-inelastic regime using a longitudinally polarized 5.9 GeV electron beam
and a longitudinally polarized proton target at Jefferson Lab with the CEBAF
Large Acceptance Spectrometer (CLAS). The data were collected over a large
kinematic phase space and divided into 110 four-dimensional bins of ,
, and . Large values of asymmetry moments clearly indicate a
substantial contribution to the polarized structure functions from transverse
virtual photon amplitudes. The interpretation of experimental data in terms of
generalized parton distributions (GPDs) provides the first insight on the
chiral-odd GPDs and , and complement previous measurements
of unpolarized structure functions sensitive to the GPDs and .
These data provide necessary constraints for chiral-odd GPD parametrizations
and will strongly influence existing theoretical handbag models
First measurement of the polarization observable E in the p→(γ→,π<sup>+</sup>)n reaction up to 2.25 GeV
First results from the longitudinally polarized frozen-spin target (FROST)
program are reported. The double-polarization observable E, for the reaction
, has been measured using a circularly polarized
tagged-photon beam, with energies from 0.35 to 2.37 GeV. The final-state pions
were detected with the CEBAF Large Acceptance Spectrometer in Hall B at the
Thomas Jefferson National Accelerator Facility. These polarization data agree
fairly well with previous partial-wave analyses at low photon energies. Over
much of the covered energy range, however, significant deviations are observed,
particularly in the high-energy region where high-L multipoles contribute. The
data have been included in new multipole analyses resulting in updated nucleon
resonance parameters. We report updated fits from the Bonn-Gatchina, J\"ulich,
and SAID groups.Comment: 6 pages, 3 figure
A Long-Term Follow-up after Cardiac Transplantation in a Lupus Patient: Case Report and Review of the Literature
Measurements of at 1.6 < W < 2.0 GeV and extraction of nucleon resonance electrocouplings at CLAS
24 pages, 22 figures. arXiv admin note: substantial text overlap with arXiv:0709.1946International audienceDifferential cross sections of the exclusive process were measured with good precision in the range of the photon virtuality GeV, and the invariant mass range of the final state GeV using the CEBAF Large Acceptance Spectrometer. Data were collected with nearly complete coverage in the azimuthal and polar angles of the center-of-mass system. More than 37,000 cross section points were measured. The contributions of the isospin resonances , and were extracted at different values of using a single-channel, energy-dependent resonance amplitude analysis. Two different approaches, the unitary isobar model and the fixed- dispersion relations, were employed in the analysis. We observe significant strength of the in the amplitude, which is in strong disagreement with quark models that predict both transverse amplitudes to be strongly suppressed. For the we observe a slow changeover from the dominance of the amplitude at the real photon point () to a where begins to dominate. The scalar amplitude drops rapidly with consistent with quark model prediction. For the resonance our analysis shows significant strength for the amplitude at GeV