[en] Here, beam-target double-spin asymmetries and target single-spin asymmetries in exclusive π"+ and quasiexclusive π"– electroproduction were obtained from scattering of 1.6- to 5.7-GeV longitudinally polarized electrons from longitudinally polarized protons (for π"+) and deuterons (for π"–) using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. The kinematic range covered is 1.1 < W < 2.6 GeV and 0.05 < Q"2 < 5GeV"2, with good angular coverage in the forward hemisphere. The asymmetry results were divided into approximately 40 000 kinematic bins for π"+ from free protons and 15 000 bins for π"– production from bound nucleons in the deuteron. The present results are found to be in reasonable agreement with fits to previous world data for W < 1.7 GeV and Q"2 < 0.5GeV"2, with discrepancies increasing at higher values of Q"2, especially for W > 1.5 GeV. Very large target-spin asymmetries are observed for W > 1.6 GeV. When combined with cross-section measurements, the present results can provide powerful constraints on nucleon resonance amplitudes at moderate and large values of Q"2, for resonances with masses as high as 2.3 GeV.

[en] Short communication

[en] We describe the design, construction, and performance of a polarized solid target for use in electron scattering experiments with the CEBAF Large Acceptance Spectrometer. Protons and deuterons are continuously polarized by microwave-induced spin-flip transitions at 1 K and 5 T. The target operated successfully during two cycles in 1998 and 2000, providing proton and deuteron polarizations as high as 96% and 46%, respectively. The unique features of the target which permit its use inside a 4π spectrometer are stressed. Comparison is made between the target polarization measured by the traditional method of NMR and by electron elastic scattering

[en] High-statistics differential cross sections and spin-density matrix elements for the reaction γp→pω have been measured using the CEBAF large acceptance spectrometer (CLAS) at Jefferson Lab for center-of-mass (c.m.) energies from threshold up to 2.84 GeV. Results are reported in 112 10-MeV wide c.m. energy bins, each subdivided into cosθ_c.m.^ω bins of width 0.1. These are the most precise and extensive ω photoproduction measurements to date. A number of prominent structures are clearly present in the data. Many of these have not previously been observed due to limited statistics in earlier measurements.

[en] High-statistics differential cross sections for the reactions γp→pη and γp→pη^' have been measured using the CEBAF large acceptance spectrometer (CLAS) at Jefferson Lab for center-of-mass energies from near threshold up to 2.84 GeV. The η^' results are the most precise to date and provide the largest energy and angular coverage. The η measurements extend the energy range of the world's large-angle results by approximately 300 MeV. These new data, in particular the η^' measurements, are likely to help constrain the analyses being performed to search for new baryon resonance states.

[en] An event-based partial wave analysis (PWA) of the reaction γp→pω has been performed on a high-statistics dataset obtained using the CLAS at Jefferson Lab for center-of-mass energies from threshold up to 2.4 GeV. This analysis benefits from access to the world's first high-precision spin-density matrix element measurements, available to the event-based PWA through the decay distribution of ω→π⁺π^-π⁰. The data confirm the dominance of the t-channel π⁰ exchange amplitude in the forward direction. The dominant resonance contributions are consistent with the previously identified states F₁₅(1680) and D₁₃(1700) near threshold, as well as the G₁₇(2190) at higher energies. Suggestive evidence for the presence of a J^P=5/2⁺ state around 2 GeV, a ''missing'' state, has also been found. Evidence for other states is inconclusive.

[en] We report the first measurement of the transverse momentum dependence of double-spin asymmetries in semi-inclusive production of pions in deep-inelastic scattering off the longitudinally polarized proton. Data have been obtained using a polarized electron beam of 5.7 GeV with the CLAS detector at the Jefferson Lab (JLab). Modulations of single spin asymmetries over the azimuthal angle between lepton scattering and hadron production planes φ have been measured over a wide kinematic range in Bjorken x and virtual photon squared four-momentum Q². A significant nonzero sin2φ single spin asymmetry was observed for the first time indicating strong spin-orbit correlations for transversely polarized quarks in the longitudinally polarized proton.

[en] We present the Bjorken integral extracted from Jefferson Lab experiment EG1b for 0.05< Q²<2.92 GeV². The integral is fit to extract the twist-4 element f₂^p-n which appears to be relatively large and negative. Systematic studies of this higher twist analysis establish its legitimacy at Q² around 1 GeV². We also performed an isospin decomposition of the generalized forward spin polarizability γ₀. Although its isovector part provides a reliable test of the calculation techniques of chiral perturbation theory, our data disagree with the calculations.

[en] We have measured the ³He(e,e^'pp)n reaction at an incident energy of 4.7 GeV over a wide kinematic range. We identified spectator correlated pp and pn nucleon pairs by using kinematic cuts and measured their relative and total momentum distributions. This is the first measurement of the ratio of pp to pn pairs as a function of pair total momentum p_tot. For pair relative momenta between 0.3 and 0.5 GeV/c, the ratio is very small at low p_tot and rises to approximately 0.5 at large p_tot. This shows the dominance of tensor over central correlations at this relative momentum.

[en] Beam-recoil transferred polarizations for the exclusive e-vectorp→e^'K⁺Λ-vector,Σ-vector⁰ reactions have been measured using the Continuous Electron Beam Accelerator Facility's large acceptance spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility. New measurements have been completed at beam energies of 4.261 and 5.754 GeV that span a range of momentum transfer Q² from 0.7 to 5.4 GeV², invariant energy W from 1.6 to 2.6 GeV, and the full center-of-mass angular range of the K⁺ meson. These new data add to the existing CLAS K⁺Λ measurements at 2.567 GeV, and provide the first-ever data for the K⁺Σ⁰ channel in electroproduction. Comparisons of the data with several theoretical models are used to study the sensitivity to s-channel resonance contributions and the underlying reaction mechanism. Interpretations within two semiclassical partonic models are made to probe the underlying reaction mechanism and the ss quark-pair creation dynamics.