Beam normal spin asymmetry for the $ep\to e\Delta (1232)$ process

Abstract

We calculate the single spin asymmetry for the $ep\to e\Delta (1232)$ process, for an electron beam polarized normal to the scattering plane. Such single spin asymmetries vanish in the one-photon exchange approximation, and are directly proportional to the absorptive part of a two-photon exchange amplitude. As the intermediate state in such two-photon exchange process is on its mass shell, the asymmetry allows one to access for the first time the on-shell $\Delta \to \Delta$ as well as $N^{\ast }\to \Delta$ electromagnetic transitions. We present the general formalism to describe the $ep\to e\Delta$ beam normal spin asymmetry, and provide a numerical estimate of its value using the nucleon, $\Delta (1232)$, $S_{11}(1535)$, and $D_{13}(1520)$ intermediate states. We compare our results with the first data from the Qweak@JLab experiment and give predictions for the A4@MAMI experiment.

18 pages, 9 figures

References in corpus (8)

• Unitary Isobar Model - MAID2007
• Electromagnetic excitation of the Delta(1232)-resonance
• Two-Photon Physics in Hadronic Processes
• Gamma-Z box contributions to parity violating elastic e-p scattering
• Chiral effective-field theory in the Delta(1232) region: II. radiative pion photoproduction
• Radiative pi0 photoproduction on protons in the Delta+(1232) region
• Transverse Beam Spin Asymmetries at Backward Angles in Elastic Electron-Proton and Quasi-elastic Electron-Deuteron Scattering
• Chiral symmetry and the axial nucleon to Delta(1232) transition form factors