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
B. Gou, J. Arvieux, K. Aulenbacher, D. Balaguer Ríos, S. Baunack, D. Becker, L. Capozza, W. Deconinck, J. Diefenbach, R. Frascaria, M. Gorchtein, B. Gläser, D. … 展开作者
B. Gou, J. Arvieux, K. Aulenbacher, D. Balaguer Ríos, S. Baunack, D. Becker, L. Capozza, W. Deconinck, J. Diefenbach, R. Frascaria, M. Gorchtein, B. Gläser, D. von Harrach, Y. Imai, E. M. Kabuß, R. Kothe, S. Kowalski, R. Kunne, F. E. Maas, H. Merkel, M. C. Mora Espí, M. Morlet, U. Müller, S. Ong, E. Schilling, C. Weinrich, J. van de Wiele, M. Zambrana, I. Zimmermann
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 $30^{\circ} < θ< 40^{\circ}$. 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 $\mathrm{πN}$ inelastic intermediate states, suggests that there are other inelastic intermediate states such as $\mathrm{ππN}$, $\mathrm{K Λ}$ and $\mathrm{ηN}$. Covering a wide energy range, our new high-precision data provide a benchmark to study those intermediate states.
Cross section and single transverse target spin asymmetry for backward pion electroproduction
核子-介子跃迁分布振幅（TDA）是核子-介子态之间非定域三夸克算符的非对角矩阵元，它是在共线因式分解描述的介子从核子反向排斥电生过程中产生的.下面我们将讨论π介子到核子时间分辨模型的问题。我们提出了一个因式分解的四重分布与软π介子定理的输入π N TDAs的。为了满足多项式性质在其完整的形式的频谱表示补充与D-项一样的贡献，从核子交换的u-通道的反应。我们提出了我们的估计后向π介子电产生非极化截面和它的横向目标单自旋不对称性在我们的复合模型为π N TDAs。
