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arXiv · 1708.05316

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

Carl E. Carlson·Barbara Pasquini·Vladyslav Pauk·Marc Vanderhaeghen
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Abstract

We calculate the single spin asymmetry for the $e p \to e \Delta(1232)$ 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 $e p \to e \Delta$ 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.

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Carl E. Carlson, Barbara Pasquini, Vladyslav Pauk, Marc Vanderhaeghen. 2017-08-17. Beam normal spin asymmetry for the $e p \to e \Delta(1232)$ process. https://doi.org/10.1103/physrevd.96.113010

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