Target and beam-target spin asymmetries in exclusive pion electroproduction for Q(2) > 1 GeV2. I. ep -> e pi(+)n
Bosted, P. E. Griffioen, Keith A
Bosted, P. E.
Griffioen, Keith A
Abstract
Beam-target double-spin asymmetries and target single-spin asymmetries were measured for the exclusive pi(+) electroproduction reaction. gamma(*) p -> n pi(+). 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 < Q(2) < 6 GeV2. Results were obtained for about 6000 bins in W, Q(2), cos(theta(*)), and phi(*). 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 Q(2), for resonances with masses as high as 2.4 GeV.
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2017-03-20
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Physics
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https://doi.org/10.1103/PhysRevC.95.035206