Zhujun Li

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

We study contributions from baryon resonance excitations to the [ital Q][sup 2] dependence of the Gerasimov-Drell-Hearn sum rule. The results indicate that the sum rule at small [ital Q][sup 2] is largely saturated by contributions from the lower mass resonant states. We find a strong [ital Q][sup 2] dependence of the resonant contributions, leading even to a sign change of the sum rule integral at [ital Q][sup 2][congruent]0.8 GeV[sup 2]. The global [ital Q][sup 2] dependence indicates discrepancies to the interpretation of the European Muon Collaboration polarized structure function data on [ital A][sub 1][sup [ital p]] in the resonance region.

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

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.

ON THRESHOLD PION PHOTOPRODUCTION AND LOW-ENERGY THEOREMS

We show that low-energy data from the neutral-pion photoproduction reaction can be adequately described without resort to exotic mechanisms. An apparent discrepancy, which has been linked to recent measurements, appears to be due to assumptions regarding the rescattering correction and coupling constants. Consequences of this result are discussed.