Beam normal single-spin asymmetry measurements at MAMI

Reaching new precision frontiers in nuclear physics brings up new experimental challenges as well as the demand for more sophisticated theoretical calculations. Especially in parity violating electron scattering experiments the contribution from higher order processes, such as two-photon exchange, is comparable in size with the observed asymmetry A_pv. Hence, a precise knowledge of this contribution is mandatory to determine the systematic uncertainties. The beam normal single-spin asymmetry A_n is a direct probe of the imaginary part of the two-photon exchange amplitude in the elastic scattering of transversely polarized electrons from unpolarized nucleons. Up to now, there is significant disagreement between experiment and theory for ²⁰⁸Pb, which motivates more measurements to study the Q² and Z dependence. Therefore a new experimental campaign started at the Mainz Microtron (MAMI) using the spectrometer setup of the A1 collaboration. Within three weeks of beam time A_n was measured as a function of Q² for ¹²C. First results for four different 4-momentum transfer values, ranging from 0.02 to 0.05 (GeV/c)², are presented in this talk.