Beam-target double-spin asymmetries and target single-spin asymmetries were measured for the exclusive π+ electroproduction reaction γ∗p→nπ+. 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 range covered is 1.1<W<3 GeV and 1<Q2<6GeV2. Results were obtained for about 6000 bins in W, Q2, cos(θ∗), and φ∗. Except at forward angles, very large target-spin asymmetries are observed over the entire W region. Reasonable agreement is found with phenomenological fits to previous data for W<1.6 GeV, but very large differences are seen at higher values of W. A generalized parton distributions (GPD)-based model is in poor agreement with the data. When combined with cross-sectional measurements, the present results provide powerful constraints on nucleon resonance amplitudes at moderate and large values of Q2, for resonances with masses as high as 2.4 GeV.
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|Titolo:||Target and beam-target spin asymmetries in exclusive pion electroproduction for Q2>1 GeV2. I. ep→eπ+n|
|Data di pubblicazione:||2017|
|Appare nelle tipologie:||03.1 Articolo su rivista|