First Measurement of the Beam Normal Single Spin Asymmetry in $\mathrm{\Delta }$ Resonance Production by $Q_{\mathrm{w}\mathrm{e}\mathrm{a}\mathrm{k}}$

The beam normal single spin asymmetry ($B_{\mathrm{n}}$) is generated in the scattering of transversely polarized electrons from unpolarized nuclei. The asymmetry arises from the interference of the imaginary part of the two-photon exchange with the one-photon exchange amplitude. The $Q_{\mathrm{w}\mathrm{e}\mathrm{a}\mathrm{k}}$ experiment has made the first measurement of $B_{\mathrm{n}}$ in the production of the $\mathrm{\Delta }$(1232) resonance, using the $Q_{\mathrm{w}\mathrm{e}\mathrm{a}\mathrm{k}}$ apparatus in Hall-C at the Thomas Jefferson National Accelerator Facility. The final transverse asymmetry, corrected for backgrounds and beam polarization, is $B_{\mathrm{n}}$ = 43 $\pm$ 16 ppm at beam energy 1.16 GeV at an average scattering angle of about 8.3 degrees, and invariant mass of 1.2 GeV. The measured preliminary $B_{\mathrm{n}}$ agrees with a preliminary theoretical calculation. $B_{\mathrm{n}}$ for the $\mathrm{\Delta }$ is the only known observable that is sensitive to the $\mathrm{\Delta }$ elastic form-factors ($\gamma$*$\mathrm{\Delta }\mathrm{\Delta }$) in addition to the generally studied transition form-factors ($\gamma$*N$\mathrm{\Delta }$), but extracting this information will require significant theoretical input.