What do we know about the Q2 evolution of the Gerasimov-Drell-Hearn sum rule?

Abstract

We study contributions from baryon resonance excitations to the Q2 dependence of the Gerasimov‐Drell‐Hearn sum rule. The results indicate that the sum rule at small Q2 is largely saturated by contribution from the lower mass resonant states. We find a strong Q2 dependence of the resonant contributions, leading even to a sign change of the sum rule integral at Q2∼0.8 GeV2. The global Q2 dependence indicates discrepencies to the interpretation of the EMC polarized structure function data on Ap1 in the resonance region, which can be largely attributed to the elimination of the P33(1232) resonance from the EMC analysis.