Single and double spin asymmetries for deeply virtual Compton scattering measured with CLAS and a longitudinally polarized proton target

Abstract

Single-beam, single-target, and double spin asymmetries for hard exclusive electroproduction of a photon on the proton $\stackrel{\ensuremath{\rightarrow}}{e}\stackrel{\ensuremath{\rightarrow}}{p}\ensuremath{\rightarrow}{e}^{\ensuremath{'}}{p}^{\ensuremath{'}}\ensuremath{\gamma}$ are presented. The data were taken at Jefferson Lab using the CEBAF large acceptance spectrometer and a longitudinally polarized $^{14}{\mathrm{NH}}_{3}$ target. The three asymmetries were measured in 165 four-dimensional kinematic bins, covering the widest kinematic range ever explored simultaneously for beam and target-polarization observables in the valence quark region. The kinematic dependences of the obtained asymmetries are discussed and compared to the predictions of models of generalized parton distributions. The measurement of three DVCS spin observables at the same kinematic points allows a quasi-model-independent extraction of the imaginary parts of the $H$ and $\stackrel{\texttildelow{}}{H}$ Compton form factors, which give insight into the electric and axial charge distributions of valence quarks in the proton.