First measurement of the Gerasimov-Drell-Hearn integral for 1 H from 200 to 800 MeV

A direct measurement of the helicity dependence of the total photoabsorption cross section an the proton was carried out at MAMI (Mainz) in the energy range 200 lt E-[gamma] lt 800 MeV. The experiment used a 4[pi] detection system, a circularly polarized. tagged photon beam, and a frozen spin target. The contributions to the Gerasimov-Drell-Hearn sum rule and to the forward spin polarizability gamma (0) determined from the data are 226 +/- 5(stat) +/- 12(syst) mub and -187 +/- 8(stat) +/- 10(syst) x 10(-6) fm(4), respectively, for 200 lt E-[gamma] lt 800 MeV.