Proton Form Factor Ratio, ${\mu }_p{G}_E^p/G_M^p$ from Double Spin Asymmetry

Abstract

The ratio of the electric and magnetic form factor of the proton, ${\mu }_p{G}_E^p/G_M^p$, has been measured for elastic electron-proton scattering with polarized beam and target up to four-momentum transfer squared, $Q^2=5.66$ (GeV/c)${}^2$ using the double spin asymmetry for target spin orientation aligned nearly perpendicular to the beam momentum direction. This measurement of ${\mu }_p{G}_E^p/G_M^p$ agrees with the $Q^2$ dependence of previous recoil polarization data and reconfirms the discrepancy at high $Q^2$ between the Rosenbluth and the polarization-transfer method with a different measurement technique and systematic uncertainties uncorrelated to those of the recoil-polarization measurements. The form factor ratio at $Q^2$=2.06 (GeV/c)${}^2$ has been measured as ${\mu }_p{G}_E^p/G_M^p=0.720\pm 0.176_{stat}\pm 0.039_{sys}$, which is in agreement with an earlier measurement with the polarized target technique at similar kinematics. The form factor ratio at $Q^2$=5.66 (GeV/c)${}^2$ has been determined as ${\mu }_p{G}_E^p/G_M^p=0.244\pm 0.353_{stat}\pm 0.013_{sys}$, which represents the highest $Q^2$ reach with the double spin asymmetry with polarized target to date.

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• 50 Years of Quantum Chromodynamics
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• Understanding the systematic differences in extractions of the proton electric form factors at low-$Q^2$
• Electromagnetic nucleon form factors in the extended vector meson dominance model
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• Reliability Analysis of the Results of the Known Experiments on Measuring of the Sachs Form Factor Ratio Using the Rosenbluth Technique. Polarization of the Final Proton in the $e\vec{p}\to e\vec{p}$ Elastic Process
• Angular Dependence of the Polarization Transfer to the Proton in the $e\vec{p}\to e\vec{p}$ Process
• Resonance Contributions to Radiative Corrections in Charged-Current Elastic (Anti)Neutrino-Nucleon Scattering at GeV Energies