Speaker
Description
Pushing the precision frontiers further in nuclear physics brings up new experimental challenges as well as the demand for more sophisticated theoretical calculations. Especially in parity- violation 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.
Beam-normal single spin asymmetries $A_{n}$ (or the so-called transverse asymmetries) are 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 $^{208}$Pb, which motivates more measurements to study the Q$^{2}$ and Z dependence. During a successful campaign at the MAinz MIcrotron (MAMI) using the spectrometer setup of the A1 collaboration, the Q$^{2}$ dependence of $A_{n}$ for $^{12}$C was determined. The follow-up experiments on $^{28}$Si and $^{90}$Zr investigated the charge dependence of the transverse asymmetry and have paved the way for a future experiment on $^{208}$Pb, thus benchmarking the theoretical calculations in the heavier mass regime.
