[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] The exclusive channel p-vectore-vector,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 A_1/2 and S_1/2 for the Roper resonance N(1400)P₁₁ and the N(1535)S₁₁ and N(1520)D₁₃ states

[en] We present results on the electroexcitation of the low mass resonances Δ(1232)P₃₃, N(1440)P₁₁, N(1520)D₁₃, and N(1535)S₁₁ in a wide range of Q². The results were obtained in the comprehensive analysis of data from the Continuous Electron Beam Accelerator Facility (CEBAF) large acceptance spectrometer (CLAS) detector at the Thomas Jefferson National Accelerator Facility (JLab) on differential cross sections, longitudinally polarized beam asymmetries, and longitudinal target and beam-target asymmetries for π electroproduction off the proton. The data were analyzed using two conceptually different approaches--fixed-t dispersion relations and a unitary isobar model--allowing us to draw conclusions on the model sensitivity of the obtained electrocoupling amplitudes. The amplitudes for the Δ(1232)P₃₃ show the importance of a meson-cloud contribution to quantitatively explain the magnetic dipole strength, as well as the electric and scalar quadrupole transitions. They do not show any tendency of approaching the pQCD regime for Q²≤6 GeV². For the Roper resonance, N(1440)P₁₁, the data provide strong evidence that this state is a predominantly radial excitation of a three-quark (3q) ground state. Measured in pion electroproduction, the transverse helicity amplitude for the N(1535)S₁₁ allowed us to obtain the branching ratios of this state to the πN and ηN channels via comparison with the results extracted from η electroproduction. The extensive CLAS data also enabled the extraction of the γ*p→N(1520)D₁₃ and N(1535)S₁₁ longitudinal helicity amplitudes with good precision. For the N(1535)S₁₁, these results became a challenge for quark models and may be indicative of large meson-cloud contributions or of representations of this state that differ from a 3q excitation. The transverse amplitudes for the N(1520)D₁₃ clearly show the rapid changeover from helicity-3/2 dominance at the real photon point to helicity-1/2 dominance at Q²>1 GeV², confirming a long-standing prediction of the constituent quark model.