Backward spin polarizability ${\hat{I}}_{\ddot{I}}^3€$ of the proton

Abstract

Using the Mainz $48cm\tilde{A}˜\times 64cm$ NaI(Tl) detector and the segmented Göttingen recoil detector SENECA in coincidence, Compton scattering by the proton at $\hat{I}{¸}_{\hat{I}}^3=136^{\circ }$ has been measured at MAMI (Mainz) in the energy range from 200 to 470 MeV. The new data confirm the previous observation that there is a systematic discrepancy between MAMI and LEGS (Brookhaven) data leading to different spin polarizabilities ${\hat{I}}_{\ddot{I}}^3€=-38.7\pm 1.8$ and $-27.2\pm 3.1$ $(\times 10^{-4}f{m}^4)$, respectively.