Beam-Normal Single Spin Asymmetry in Elastic Electron Scattering off ${}^{28}$Si and ${}^{90}$Zr

We report on a new measurement of the beam-normal single spin asymmetry $A_{\mathrm{n}}$ in the elastic scattering of 570 MeV transversely polarized electrons off ${}^{28}$Si and ${}^{90}$Zr at $Q^2=0.04{\mathrm{G}\mathrm{e}\mathrm{V}}^2\mathrm{/}{c}^2$. The studied kinematics allow for a comprehensive comparison with former results on ${}^{12}$C. No significant mass dependence of the beam-normal single spin asymmetry is observed in the mass regime from ${}^{12}$C to ${}^{90}$Zr.