Target and beam-target spin asymmetries in exclusive pion electroproduction for $Q^2>1$ GeV${}^2$. II. $ep\to e{\pi }^{0}p$

Abstract

Beam-target double-spin asymmetries and target single-spin asymmetries were measured for the exclusive ${\pi }^0$ electroproduction reaction ${\gamma }^{\ast }p\to p{\pi }^0$, expanding an analysis of the ${\gamma }^{\ast }p\to n{\pi }^{+}$ 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 Lab. The kinematic range covered is $1.1<W<3$ GeV and $1<Q^2<6$ GeV${}^2$. Results were obtained for about 5700 bins in $W$, $Q^2$, \cthcm, and ${\varphi }^{\ast }$. The beam-target asymmetries were found to generally be greater than zero, with relatively modest \phicmsp dependence. The target asymmetries exhibit very strong \phicmsp dependence, with a change in sign occurring between results at low $W$ and high $W$, in contrast to ${\pi }^{+}$ 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 section measurements, as well as ${\pi }^{+}$ observables, the present results will 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.

arXiv comment28 pages, 12 figures, submitted to Phys. Rev. C

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Cited by in corpus (4)

• The Spin Structure of the Nucleon
• Jülich-Bonn-Washington Model for Pion Electroproduction Multipoles
• Extraction of beam-spin asymmetries from the hard exclusive ${\pi }^{+}$ channel off protons in a wide range of kinematics
• Prospects for quarkonium studies at the high-luminosity LHC