Chinese Acad Sci, Inst High Energy Phys, Beijing 100039, Peoples R China
; Natl Lab Heavy Ion Collis, Ctr Theoret Nucl Phys, Lanzhou 730000, Peoples R China
; Univ Adelaide, Dept Phys & Math Phys, Adelaide, SA 5005, Australia
; Univ Adelaide, Special Res Ctr Subatom Struct Matter, Adelaide, SA 5005, Australia
; Chinese Acad Sci, Inst Modern Phys, Lanzhou 730000, Peoples R China
We test the Gerasimov-Drell-Hearn (GDH) sum rule numerically by calculating the total photon absorption cross sections sigma(1/2) and sigma(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, sigma(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) excitation largely saturates the sum rule at Q(2) = 0, and dominates at small Q(2). The GDH integral has a strong Q(2)-dependence below Q(2) = 1.0GeV(2) and changes its sign around Q(2) = 0.3GeV(2). It becomes weakly Q2-dependence for Q(2) > 1.0GeV(2) because of the quick decline of resonance contributions.