Measurement of Target and Double-spin Asymmetries for the $\vec e\vec p o e\pi^+ (n)$ Reaction in the Nucleon Resonance Region at Low $Q^2$

摘要

We report measurements of target- and double-spin asymmetries for theexclusive channel $\vec e\vec p\to e\pi^+ (n)$ in the nucleon resonance regionat Jefferson Lab using the CEBAF Large Acceptance Spectrometer (CLAS). Theseasymmetries were extracted from data obtained using a longitudinally polarizedNH$_3$ target and a longitudinally polarized electron beam with energies 1.1,1.3, 2.0, 2.3 and 3.0 GeV. The new results are consistent with previous CLASpublications but are extended to a low $Q^2$ range from $0.0065$ to $0.35$(GeV$/c$)$^2$. The $Q^2$ access was made possible by a custom-built Cherenkovdetector that allowed the detection of electrons for scattering angles as lowas $6^\circ$. These results are compared with the unitary isobar models JANRand MAID, the partial-wave analysis prediction from SAID and the dynamic modelDMT. In many kinematic regions our results, in particular results on the targetasymmetry, help to constrain the polarization-dependent components of thesemodels.