Vector analyzing power in elastic electron-proton scattering
We compute the vector analyzing power (VAP) for the elastic scattering of transversely polarized electrons from protons at low energies using an effective theory of electrons, protons, and photons. We study all contributions through second order in E/M, where E and M are the electron energy and nucleon mass, respectively. The leading-order VAP arises from the imaginary part of the interference of one- and two-photon exchange amplitudes. Subleading contributions are generated by the nucleon magnetic moment and charge radius as well as recoil corrections to the leading-order amplitude. Working to O(E/M)the 2nd , we obtain a prediction for An that is free of unknown parameters and that agrees with the recent measurement of the VAP in backward angle ep scattering.
Additional Information© 2004 The American Physical Society. Received 18 May 2004; published 11 November 2004. It is a pleasure to thank C. Bauer, V. Cirigliano, B. Holstein, T. Ito, A. Kurylov, Y. Kolomensky, K. Kumar, F. Maas, D. Mack, C. Maekawa, R. D. McKeown, G. Prezeau, P.A. Souder, U. van Kolck, P. Vogel, and S.P. Wells for useful discussions. This work was supported in part under DOE Contract No. DE-FG03-88ER40397 and NSF Grant No. PHY-0071856.
Published - DIAprc04.pdf