Target and beam-target spin asymmetries in exclusive pion electroproduction for Q2>1 GeV2. II. ep→eπ0p TARGET and BEAM-TARGET SPIN .... II. ... P. E. BOSTED et al.

Abstract

© 2017 American Physical Society. Beam-target double-spin asymmetries and target single-spin asymmetries were measured for the exclusive π0 electroproduction reaction γ∗p→pπ0, expanding an analysis of the γ∗p→nπ+ reaction from the same experiment. The results were obtained from scattering of 6-GeV longitudinally polarized electrons off longitudinally polarized protons using the CEBAF Large Acceptance Spectrometer at Jefferson Laboratory. The kinematic ranges covered are 1.1<W<3 GeV and 1<Q2<6 GeV2. Results were obtained for about 5700 bins in W, Q2, cos(θ∗), and φ∗. The beam-target asymmetries were found to generally be greater than zero, with relatively modest φ∗ dependence. The target asymmetries exhibit very strong φ∗ dependence, with a change in sign occurring between results at low W and high W, in contrast to π+ electroproduction. Reasonable agreement is found with phenomenological fits to previous data for W<1.6 GeV, but significant differences are seen at higher W. When combined with cross-sectional measurements, as well as π+ observables, the present results will provide powerful constraints on nucleon resonance amplitudes at moderate and large values of Q2, for resonances with masses as high as 2.4 GeV.