Vertical Beam Polarization at MAMI

TL;DR

This paper reports the first use of a vertically polarized electron beam at MAMI to measure beam-normal single-spin asymmetry in electron-carbon scattering, involving novel polarization orientation and measurement techniques.

Contribution

It introduces a method to orient and determine vertical electron polarization at MAMI, enabling new asymmetry measurements beyond previous capabilities.

Findings

Successful vertical polarization orientation at MAMI

Measurement of beam-normal single-spin asymmetry in $^{12}C$

Development of a method to determine vertical polarization magnitude and orientation

Abstract

For the first time a vertically polarized electron beam has been used for physics experiments at MAMI in the energy range between 180 and 855 MeV. The beam-normal single-spin asymmetry $A_{\mathrm{n}}$, which is a direct probe of higher-order photon exchange beyond the first Born approximation, has been measured in the reaction $^{12}\mathrm C(\vec e,e')^{12}\mathrm C$. Vertical polarization orientation was necessary to measure this asymmetry with the existing experimental setup. In this paper we describe the procedure to orient the electron polarization vector vertically, and the concept of determining both its magnitude and orientation with the available setup. A sophisticated method has been developed to overcome the lack of a polarimeter setup sensitive to the vertical polarization component.