The Reactionγp→π0γ′pand the Magnetic Dipole Moment of theΔ+(1232)Resonance

The reaction $\gamma p\to {\pi }^0{\gamma }^{\prime }p$ has been measured with the TAPS calorimeter at the Mainz Microtron accelerator facility MAMI for energies between $\sqrt{s}=1221–1331\mathrm{M}\mathrm{e}\mathrm{V}$. The cross section’s differential in angle and energy have been determined for the photon ${\gamma }^{\prime }$ in three bins of the excitation energy. This reaction channel provides access to the magnetic dipole moment of the ${\Delta }^{+}(1232)$ resonance and, for the first time, a value of ${\mu }_{{\Delta }^{+}}=\mathbf{[}{2.7}_{-1.3}^{+1.0}(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t})\pm 1.5(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t})\pm 3(\mathrm{t}\mathrm{h}\mathrm{e}\mathrm{o}\mathrm{r})\mathbf{]}{\mu }_N$ has been extracted.