Abstract
We test the Gerasimov-Drell-Hearn (GDH) sum rule numerically by calculating the total photon absorption cross sections σ 1 2 and σ 3 2 on the nucleon via photon excitation of baryon resonances in the constituent quark model. A total of seventeen, low-lying, non-strange baryon resonances are included in this calculation. The transverse and longitudinal interference cross section, σ 1 2 TL , is found to play an important role in the study of the Q 2 variation of the sum rule. The results show that the GDH sum rule is saturated by these resonances at a confidence level of 94%. In particular, the P 33(1232) dominates at small Q 2. The GDH integral has a strong Q 2-dependence below Q 2 = 1.0 GeV 2 and changes its sign around Q 2 = 0.3 GeV 2. It becomes weakly Q 2-dependent for Q 2 > 1.0 GeV 2 because of the quick decline of the resonance contributions.
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