학술논문
Study of Two-Photon Exchange via the Beam Transverse Single Spin Asymmetry in Electron-Proton Elastic Scattering at Forward Angles over a Wide Energy Range
Document Type
Working Paper
Author
Gou, B.; Arvieux, J.; Aulenbacher, K.; Ríos, D. Balaguer; Baunack, S.; Becker, D.; Capozza, L.; Deconinck, W.; Diefenbach, J.; Frascaria, R.; Gorchtein, M.; Gläser, B.; von Harrach, D.; Imai, Y.; Kabuß, E. M.; Kothe, R.; Kowalski, S.; Kunne, R.; Maas, F. E.; Merkel, H.; Espí, M. C. Mora; Morlet, M.; Müller, U.; Ong, S.; Schilling, E.; Weinrich, C.; van de Wiele, J.; Zambrana, M.; Zimmermann, I.
Source
Phys. Rev. Lett. 124, 122003 (2020)
Subject
Language
Abstract
We report on a new measurement of the beam transverse single spin asymmetry in electron-proton elastic scattering, $A^{ep}_{\perp}$, at five beam energies from 315.1 MeV to 1508.4 MeV and at a scattering angle of $30^{\circ} < \theta < 40^{\circ}$. The covered $Q^2$ values are 0.032, 0.057, 0.082, 0.218, 0.613 (GeV/c)$^2$. The measurement clearly indicates significant inelastic contributions to the two-photon-exchange (TPE) amplitude in the low-$Q^2$ kinematic region. No theoretical calculation is able to reproduce our result. Comparison with a calculation based on unitarity, which only takes into account elastic and $\mathrm{\pi N}$ inelastic intermediate states, suggests that there are other inelastic intermediate states such as $\mathrm{\pi \pi N}$, $\mathrm{K \Lambda}$ and $\mathrm{\eta N}$. Covering a wide energy range, our new high-precision data provide a benchmark to study those intermediate states.
Comment: 6 pages, 3 figures
Comment: 6 pages, 3 figures