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

TL;DR

This paper reports the first direct measurement of the Gerasimov-Drell-Hearn integral for hydrogen in the 200 to 800 MeV energy range, providing new experimental data on proton spin structure.

Contribution

It presents the first direct experimental determination of the GDH integral for hydrogen within this energy range, using advanced detection and polarized photon techniques.

Findings

GDH integral value: 226 ± 5 (stat) ± 12 (sys) μb

Forward spin polarizability: -187 ± 8 (stat) ± 10 (sys) × 10^{-6} fm^4

Data covers photon energies from 200 to 800 MeV

Abstract

A direct measurement of the helicity dependence of the total photoabsorption cross section on the proton was carried out at MAMI (Mainz) in the energy range 200 < E_gamma < 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 \pm 5 (stat)\pm 12(sys) \mu b and -187 \pm 8 (stat)\pm 10(sys)10^{-6} fm^4, respectively, for 200 < E_\gamma < 800 MeV.